Important SQL Commands

Important SQL commands with Syntax/Examples

What is SQL?

SQL is a standard language for accessing databases.

• SQL stands for Structured Query Language
• SQL lets you access and manipulate databases
• SQL is an ANSI (American National Standards Institute) standard

Our SQL tutorial will teach you how to use SQL to access and manipulate data in: MySQL, SQL Server, Access, Oracle, Sybase, DB2, and other database systems.

What Can SQL do?

• SQL can execute queries against a database
• SQL can retrieve data from a database
• SQL can insert records in a database
• SQL can update records in a database
• SQL can delete records from a database
• SQL can create new databases
• SQL can create new tables in a database
• SQL can create stored procedures in a database
• SQL can create views in a database
• SQL can set permissions on tables, procedures, and views

SQL is a Standard - BUT....

Although SQL is an ANSI (American National Standards Institute) standard, there are different versions of the SQL language.

However, to be compliant with the ANSI standard, they all support at least the major commands (such as SELECT, UPDATE, DELETE, INSERT, WHERE) in a similar manner.

RDBMS

RDBMS stands for Relational Database Management System.

RDBMS is the basis for SQL, and for all modern database systems such as MS SQL Server, IBM DB2, Oracle, MySQL, and Microsoft Access.

The data in RDBMS is stored in database objects called tables.

A table is a collection of related data entries and it consists of columns and rows.

Using SQL in Your Web Site

To build a web site that shows data from a database, you will need:

• An RDBMS database program (i.e. MS Access, SQL Server, MySQL)
• To use a server-side scripting language, like PHP or ASP
• To use SQL to get the data you want
• To use HTML / CSS

Keep in Mind That...

• SQL is NOT case sensitive: SELECT is the same as select

Semicolon after SQL Statements?

Some database systems require a semicolon at the end of each SQL statement.

Semicolon is the standard way to separate each SQL statement in database systems that allow more than one SQL statement to be executed in the same call to the server.

In this tutorial, we will use semicolon at the end of each SQL statement.

Some of the Most Important SQL Commands

• CREATE DATABASE - creates a new database
• CREATE TABLE - creates a new table
• CREATE INDEX - creates an index (search key)
• CREATE/UPDATE/DELETE VIEW –Create a virtual table
• ALTER DATABASE - modifies a database
• ALTER TABLE - modifies a table
• INSERT INTO - inserts new data into a database
• UPDATE - updates data in a database
• DELETE - deletes data from a database
• SELECT - extracts data from a database
• DROP TABLE - deletes a table
• DROP INDEX - deletes an index
• DROP Database - deletes a database

The SQL CREATE DATABASE Statement

The CREATE DATABASE statement is used to create a database.

SQL CREATE DATABASE Syntax

CREATE DATABASE dbname;

SQL CREATE DATABASE Example

The following SQL statement creates a database called "my_db":

CREATE DATABASE my_db;

Database tables can be added with the CREATE TABLE statement.

The SQL CREATE TABLE Statement

The CREATE TABLE statement is used to create a table in a database.

Tables are organized into rows and columns; and each table must have a name.

SQL CREATE TABLE Syntax

CREATE TABLE table_name
(
column_name1 data_type(size),
column_name2 data_type(size),
column_name3 data_type(size),
....
);

The column_name parameters specify the names of the columns of the table.

The data_type parameter specifies what type of data the column can hold (e.g. varchar, integer, decimal, date, etc.).

The size parameter specifies the maximum length of the column of the table.

SQL CREATE TABLE Example

Now we want to create a table called "Persons" that contains five columns: PersonID, LastName, FirstName, Address, and City.

We use the following CREATE TABLE statement:

Example

CREATE TABLE Persons
(
PersonID int,
LastName varchar(255),
FirstName varchar(255),
Address varchar(255),
City varchar(255)
);

The PersonID column is of type int and will hold an integer.

The LastName, FirstName, Address, and City columns are of type varchar and will hold characters, and the maximum length for these fields is 255 characters.

The empty "Persons" table will now look like this:

PersonID

LastName

FirstName

Address

City

Indexes

The CREATE INDEX statement is used to create indexes in tables.

Indexes allow the database application to find data fast; without reading the whole table.

An index can be created in a table to find data more quickly and efficiently.The users cannot see the indexes, they are just used to speed up searches/queries.

Note: Updating a table with indexes takes more time than updating a table without (because the indexes also need an update). So you should only create indexes on columns (and tables) that will be frequently searched against.

SQL CREATE INDEX Syntax

Creates an index on a table. Duplicate values are allowed:

CREATE INDEX index_name
ON table_name (column_name)

SQL CREATE UNIQUE INDEX Syntax

Creates a unique index on a table. Duplicate values are not allowed:

CREATE UNIQUE INDEX index_name
ON table_name (column_name)

Note: The syntax for creating indexes varies amongst different databases. Therefore: Check the syntax for creating indexes in your database.

CREATE INDEX Example

The SQL statement below creates an index named "PIndex" on the "LastName" column in the "Persons" table:

CREATE INDEX PIndex
ON Persons (LastName)

If you want to create an index on a combination of columns, you can list the column names within the parentheses, separated by commas:

CREATE INDEX PIndex
ON Persons (LastName, FirstName)

SQL CREATE VIEW Statement

A view is a virtual table.

Shows how to create, update, and delete a view.

In SQL, a view is a virtual table based on the result-set of an SQL statement.

A view contains rows and columns, just like a real table. The fields in a view are fields from one or more real tables in the database.

You can add SQL functions, WHERE, and JOIN statements to a view and present the data as if the data were coming from one single table.

SQL CREATE VIEW Syntax

CREATE VIEW view_name AS
SELECT column_name(s)
FROM table_name
WHERE condition

Note: A view always shows up-to-date data! The database engine recreates the data, using the view's SQL statement, every time a user queries a view.

SQL CREATE VIEW Examples

If you have the Northwind database you can see that it has several views installed by default.

The view "Current Product List" lists all active products (products that are not discontinued) from the "Products" table. 

The view is created with the following SQL:

CREATE VIEW [Current Product List] AS
SELECT ProductID,ProductName
FROM Products
WHERE Discontinued=No

We can query the view above as follows:

SELECT * FROM [Current Product List]

Another view , selects every product in the "Products" table with a unit price higher than the average unit price:

CREATE VIEW [Products Above Average Price] AS
SELECT ProductName,UnitPrice
FROM Products
WHERE UnitPrice>(SELECT AVG(UnitPrice) FROM Products)

We can query the view above as follows:

SELECT * FROM [Products Above Average Price]

Another view , calculates the total sale for each category in 1997. Note that this view selects its data from another view called "Product Sales for 1997":

CREATE VIEW [Category Sales For 1997] AS
SELECT DISTINCT CategoryName,Sum(ProductSales) AS CategorySales
FROM [Product Sales for 1997]
GROUP BY CategoryName

We can query the view above as follows:

SELECT * FROM [Category Sales For 1997]

We can also add a condition to the query. Now we want to see the total sale only for the category "Beverages":

SELECT * FROM [Category Sales For 1997]
WHERE CategoryName='Beverages'

SQL Updating a View

You can update a view by using the following syntax:

SQL CREATE OR REPLACE VIEW Syntax

CREATE OR REPLACE VIEW view_name AS
SELECT column_name(s)
FROM table_name
WHERE condition

Now we want to add the "Category" column to the "Current Product List" view. We will update the view with the following SQL:

Example

CREATE VIEW [Current Product List] AS
SELECT ProductID,ProductName,Category
FROM Products
WHERE Discontinued=No

SQL Dropping a View

You can delete a view with the DROP VIEW command.

SQL DROP VIEW Syntax

DROP VIEW view_name

Alter Database  Statement

Rename the Database OldDatabasename  to  NewDatabaseName
ALTER DATABASE OdDatabasename  MODIFY NAME = NewDatabaseName

The SQL INSERT Statement

The INSERT INTO statement is used to insert new records in a table.

SQL INSERT INTO Syntax

It is possible to write the INSERT INTO statement in two forms.

The first form does not specify the column names where the data will be inserted, only their values:

INSERT INTO table_name
VALUES (value1,value2,value3,...);

The second form specifies both the column names and the values to be inserted:

INSERT INTO table_name (column1,column2,column3,...)
VALUES (value1,value2,value3,...);

INSERT INTO Example

Assume we wish to insert a new row in the "Customers" table.

We can use the following SQL statement:

Example

INSERT INTO Customers (CustomerName, ContactName, Address, City, PostalCode, Country)
VALUES ('Cardinal','Tom B. Erichsen','Skagen 21','Stavanger','4006','Norway');

The selection from the "Customers" table will now look like this:

CustomerID	CustomerName	ContactName	Address	City	PostalCode	Country
87	Wartian Herkku	Pirkko Koskitalo	Torikatu 38	Oulu	90110	Finland
88	Wellington Importadora	Paula Parente	Rua do Mercado, 12	Resende	08737-363	Brazil
89	White Clover Markets	Karl Jablonski	305 - 14th Ave. S. Suite 3B	Seattle	98128	USA
90	Wilman Kala	Matti Karttunen	Keskuskatu 45	Helsinki	21240	Finland
91	Wolski	Zbyszek	ul. Filtrowa 68	Walla	01-012	Poland
92	Cardinal	Tom B. Erichsen	Skagen 21	Stavanger	4006	Norway

Insert Data Only in Specified Columns

It is also possible to only insert data in specific columns.

The following SQL statement will insert a new row, but only insert data in the "CustomerName", "City", and "Country" columns (and the CustomerID field will of course also be updated automatically):

Example

INSERT INTO Customers (CustomerName, City, Country)
VALUES ('Cardinal', 'Stavanger', 'Norway');

The selection from the "Customers" table will now look like this:

CustomerID	CustomerName	ContactName	Address	City	PostalCode	Country
87	Wartian Herkku	Pirkko Koskitalo	Torikatu 38	Oulu	90110	Finland
88	Wellington Importadora	Paula Parente	Rua do Mercado, 12	Resende	08737-363	Brazil
89	White Clover Markets	Karl Jablonski	305 - 14th Ave. S. Suite 3B	Seattle	98128	USA
90	Wilman Kala	Matti Karttunen	Keskuskatu 45	Helsinki	21240	Finland
91	Wolski	Zbyszek	ul. Filtrowa 68	Walla	01-012	Poland
92	Cardinal	null	null	Stavanger	null	Norway

The ALTER TABLE Statement

The ALTER TABLE statement is used to add, delete, or modify columns in an existing table.

SQL ALTER TABLE Syntax

To add a column in a table, use the following syntax:

ALTER TABLE table_name
ADD column_name datatype

To delete a column in a table, use the following syntax (notice that some database systems don't allow deleting a column):

ALTER TABLE table_name
DROP COLUMN column_name

To change the data type of a column in a table, use the following syntax:

SQL Server / MS Access:

ALTER TABLE table_name
ALTER COLUMN column_name datatype

My SQL / Oracle:

ALTER TABLE table_name
MODIFY COLUMN column_name datatype

Oracle 10G and later:

ALTER TABLE table_name
MODIFY column_name datatype

SQL ALTER TABLE Example

Look at the "Persons" table:

P_Id	LastName	FirstName	Address	City
1	Hansen	Ola	Timoteivn 10	Sandnes
2	Svendson	Tove	Borgvn 23	Sandnes
3	Pettersen	Kari	Storgt 20	Stavanger

Now we want to add a column named "DateOfBirth" in the "Persons" table.

We use the following SQL statement:

ALTER TABLE Persons
ADD DateOfBirth date

Notice that the new column, "DateOfBirth", is of type date and is going to hold a date. The data type specifies what type of data the column can hold. For a complete reference of all the data types available in MS Access, MySQL, and SQL Server.

The "Persons" table will now like this:

P_Id	LastName	FirstName	Address	City	DateOfBirth
1	Hansen	Ola	Timoteivn 10	Sandnes
2	Svendson	Tove	Borgvn 23	Sandnes
3	Pettersen	Kari	Storgt 20	Stavanger

Change Data Type Example

Now we want to change the data type of the column named "DateOfBirth" in the "Persons" table.

We use the following SQL statement:

ALTER TABLE Persons
ALTER COLUMN DateOfBirth year

Notice that the "DateOfBirth" column is now of type year and is going to hold a year in a two-digit or four-digit format.

DROP COLUMN Example

Next, we want to delete the column named "DateOfBirth" in the "Persons" table.

We use the following SQL statement:

ALTER TABLE Persons
DROP COLUMN DateOfBirth

The "Persons" table will now like this:

P_Id	LastName	FirstName	Address	City
1	Hansen	Ola	Timoteivn 10	Sandnes
2	Svendson	Tove	Borgvn 23	Sandnes
3	Pettersen	Kari	Storgt 20	Stavanger

The SQL UPDATE Statement

The UPDATE statement is used to update existing records in a table.

SQL UPDATE Syntax

UPDATE table_name
SET column1=value1,column2=value2,...
WHERE some_column=some_value;

Below is a selection from the "Customers" table:

CustomerID	CustomerName	ContactName	Address	City	PostalCode	Country
1	Alfreds Futterkiste	Maria Anders	Obere Str. 57	Berlin	12209	Germany
2	Ana Trujillo Emparedados y helados	Ana Trujillo	Avda. de la Constitución 2222	México D.F.	05021	Mexico
3	Antonio Moreno Taquería	Antonio Moreno	Mataderos 2312	México D.F.	05023	Mexico
4	Around the Horn	Thomas Hardy	120 Hanover Sq.	London	WA1 1DP	UK
5	Berglunds snabbköp	Christina Berglund	Berguvsvägen 8	Luleå	S-958 22	Sweden

SQL UPDATE Example

Assume we wish to update the customer "Alfreds Futterkiste" with a new contact person and city.

We use the following SQL statement:

Example

UPDATE Customers
SET ContactName='Alfred Schmidt', City='Hamburg'
WHERE CustomerName='Alfreds Futterkiste';

The selection from the "Customers" table will now look like this:

CustomerID	CustomerName	ContactName	Address	City	PostalCode	Country
1	Alfreds Futterkiste	Alfred Schmidt	Obere Str. 57	Hamburg	12209	Germany
2	Ana Trujillo Emparedados y helados	Ana Trujillo	Avda. de la Constitución 2222	México D.F.	05021	Mexico
3	Antonio Moreno Taquería	Antonio Moreno	Mataderos 2312	México D.F.	05023	Mexico
4	Around the Horn	Thomas Hardy	120 Hanover Sq.	London	WA1 1DP	UK
5	Berglunds snabbköp	Christina Berglund	Berguvsvägen 8	Luleå	S-958 22	Sweden

Update Warning!

Be careful when updating records. If we had omitted the WHERE clause, in the example above, like this:

UPDATE Customers
SET ContactName='Alfred Schmidt', City='Hamburg';

The "Customers" table would have looked like this:

CustomerID	CustomerName	ContactName	Address	City	PostalCode	Country
1	Alfreds Futterkiste	Alfred Schmidt	Obere Str. 57	Hamburg	12209	Germany
2	Ana Trujillo Emparedados y helados	Alfred Schmidt	Avda. de la Constitución 2222	Hamburg	05021	Mexico
3	Antonio Moreno Taquería	Alfred Schmidt	Mataderos 2312	Hamburg	05023	Mexico
4	Around the Horn	Alfred Schmidt	120 Hanover Sq.	Hamburg	WA1 1DP	UK
5	Berglunds snabbköp	Alfred Schmidt	Berguvsvägen 8	Hamburg	S-958 22	Sweden

The SQL DELETE Statement

The DELETE statement is used to delete records in a table.

The DELETE statement is used to delete rows in a table.

SQL DELETE Syntax

DELETE FROM table_name
WHERE some_column=some_value;

Below is a selection from the "Customers" table:

CustomerID	CustomerName	ContactName	Address	City	PostalCode	Country
1	Alfreds Futterkiste	Maria Anders	Obere Str. 57	Berlin	12209	Germany
2	Ana Trujillo Emparedados y helados	Ana Trujillo	Avda. de la Constitución 2222	México D.F.	05021	Mexico
3	Antonio Moreno Taquería	Antonio Moreno	Mataderos 2312	México D.F.	05023	Mexico
4	Around the Horn	Thomas Hardy	120 Hanover Sq.	London	WA1 1DP	UK
5	Berglunds snabbköp	Christina Berglund	Berguvsvägen 8	Luleå	S-958 22	Sweden

SQL DELETE Example

Assume we wish to delete the customer "Alfreds Futterkiste" from the "Customers" table.

We use the following SQL statement:

Example

DELETE FROM Customers
WHERE CustomerName='Alfreds Futterkiste' AND ContactName='Maria Anders';

The "Customers" table will now look like this:

CustomerID	CustomerName	ContactName	Address	City	PostalCode	Country
2	Ana Trujillo Emparedados y helados	Ana Trujillo	Avda. de la Constitución 2222	México D.F.	05021	Mexico
3	Antonio Moreno Taquería	Antonio Moreno	Mataderos 2312	México D.F.	05023	Mexico
4	Around the Horn	Thomas Hardy	120 Hanover Sq.	London	WA1 1DP	UK
5	Berglunds snabbköp	Christina Berglund	Berguvsvägen 8	Luleå	S-958 22	Sweden

Delete All Data

It is possible to delete all rows in a table without deleting the table. This means that the table structure, attributes, and indexes will be intact:

DELETE FROM table_name;
OR
DELETE * FROM table_name;

Note: Be very careful when deleting records. You cannot undo this statement!

Database Tables

A database most often contains one or more tables. Each table is identified by a name (e.g. "Customers" or "Orders"). Tables contain records (rows) with data.

Below is a selection from the "Customers" table:

CustomerID	CustomerName	ContactName	Address	City	PostalCode	Country
1	Alfreds Futterkiste	Maria Anders	Obere Str. 57	Berlin	12209	Germany
2	Ana Trujillo Emparedados y helados	Ana Trujillo	Avda. de la Constitución 2222	México D.F.	05021	Mexico
3	Antonio Moreno Taquería	Antonio Moreno	Mataderos 2312	México D.F.	05023	Mexico
4	Around the Horn	Thomas Hardy	120 Hanover Sq.	London	WA1 1DP	UK
5	Berglunds snabbköp	Christina Berglund	Berguvsvägen 8	Luleå	S-958 22	Sweden

The table above contains five records (one for each customer) and seven columns (CustomerID, CustomerName, ContactName, Address, City, PostalCode, and Country).

The SQL SELECT Statement

The SELECT statement is used to select data from a database.

The result is stored in a result table, called the result-set.

SQL SELECT Syntax

SELECT column_name,column_name
FROM table_name;

and

SELECT * FROM table_name;

SELECT Example

The following SQL statement selects the "CustomerName" and "City" columns from the "Customers" table:

Example

SELECT CustomerName,City FROM Customers

The following SQL statement selects all the columns from the "Customers" table:

Example

SELECT * FROM Customers;

The SQL SELECT DISTINCT Statement

In a table, a column may contain many duplicate values; and sometimes you only want to list the different (distinct) values.

The DISTINCT keyword can be used to return only distinct (different) values.

SQL SELECT DISTINCT Syntax

SELECT DISTINCT column_name,column_name
FROM table_name;

The following SQL statement selects only the distinct values from the "City" columns from the "Customers" table:

Example

SELECT DISTINCT City FROM Customers;

The SQL WHERE Clause 

The WHERE clause is used to extract only those records that fulfill a specified criterion.

SQL WHERE Syntax

SELECT column_name,column_name
FROM table_name
WHERE column_name operator value;

The following SQL statement selects all the customers from the country "Mexico", in the "Customers" table:

Example

SELECT * FROM Customers
WHERE Country='Mexico';

Text Fields vs. Numeric Fields

SQL requires single quotes around text values (most database systems will also allow double quotes).

However, numeric fields should not be enclosed in quotes:

Example

SELECT * FROM Customers
WHERE CustomerID=1;

Operators in The WHERE Clause

The following operators can be used in the WHERE clause:

Operator	Description
=	Equal
<>	Not equal. Note: In some versions of SQL this operator may be written as !=
>	Greater than
<	Less than
>=	Greater than or equal
<=	Less than or equal
BETWEEN	Between an inclusive range
LIKE	Search for a pattern
IN	To specify multiple possible values for a column

The SQL AND & OR Operators

The AND & OR operators are used to filter records based on more than one condition.

The AND operator displays a record if both the first condition AND the second condition are true.

The OR operator displays a record if either the first condition OR the second condition is true.

AND Operator Example

The following SQL statement selects all customers from the country "Germany" AND the city "Berlin", in the "Customers" table:

Example

SELECT * FROM Customers
WHERE Country='Germany'
AND City='Berlin';

The following SQL statement selects all customers from the city "Berlin" OR "München", in the "Customers" table: 

Example

SELECT * FROM Customers
WHERE City='Berlin'
OR City='München';

Combining AND & OR

You can also combine AND and OR (use parenthesis to form complex expressions).

The following SQL statement selects all customers from the country "Germany" AND the city must be equal to "Berlin" OR "München", in the "Customers" table:

Example

SELECT * FROM Customers
WHERE Country='Germany'
AND (City='Berlin' OR City='München');

The ORDER BY keyword is used to sort the result-set.

The SQL ORDER BY Keyword

The ORDER BY keyword is used to sort the result-set by one or more columns.

The ORDER BY keyword sorts the records in ascending order by default. To sort the records in a descending order, you can use the DESC keyword.

SQL ORDER BY Syntax

SELECT column_name,column_name
FROM table_name
ORDER BY column_name,column_name ASC|DESC;

ORDER BY Example

The following SQL statement selects all customers from the "Customers" table, sorted by the "Country" column:

Example

SELECT * FROM Customers
ORDER BY Country;

ORDER BY DESC Example

The following SQL statement selects all customers from the "Customers" table, sorted DESCENDING by the "Country" column:

Example

SELECT * FROM Customers
ORDER BY Country DESC;

ORDER BY Several Columns Example

The following SQL statement selects all customers from the "Customers" table, sorted by the "Country" and the "CustomerName" column:

Example

SELECT * FROM Customers
ORDER BY Country,CustomerName;

Indexes, tables, and databases can easily be deleted/removed with the DROP statement.

The DROP INDEX Statement

The DROP INDEX statement is used to delete an index in a table.

DROP INDEX Syntax for MS Access:

DROP INDEX index_name ON table_name

DROP INDEX Syntax for MS SQL Server:

DROP INDEX table_name.index_name

DROP INDEX Syntax for DB2/Oracle:

DROP INDEX index_name

DROP INDEX Syntax for MySQL:

ALTER TABLE table_name DROP INDEX index_name

The DROP TABLE Statement

The DROP TABLE statement is used to delete a table.

DROP TABLE table_name

The DROP DATABASE Statement

The DROP DATABASE statement is used to delete a database.

DROP DATABASE database_name

The TRUNCATE TABLE Statement

What if we only want to delete the data inside the table, and not the table itself?

Then, use the TRUNCATE TABLE statement:

TRUNCATE TABLE table_name

The SQL SELECT INTO Statement

With SQL, you can copy information from one table into another.The SELECT INTO statement copies data from one table and inserts it into a new table.The SELECT INTO statement selects data from one table and inserts it into a new table.

SQL SELECT INTO Syntax

We can copy all columns into the new table:

SELECT *
INTO newtable [IN externaldb]
FROM table1;

Or we can copy only the columns we want into the new table:

SELECT column_name(s)
INTO newtable [IN externaldb]
FROM table1;

SQL SELECT INTO Examples

Create a backup copy of Customers:

SELECT * INTO CustomersBackup2013 FROM Customers;

Use the IN clause to copy the table into another database:

SELECT * INTO CustomersBackup2013 IN 'Backup.mdb' FROM Customers;

Copy only a few columns into the new table:

SELECT CustomerName, ContactName INTO CustomersBackup2013 FROM Customers;

Copy only the German customers into the new table:

SELECT * INTO CustomersBackup2013 FROM Customers WHERE Country='Germany';

Copy data from more than one table into the new table:

SELECT Customers.CustomerName, Orders.OrderID INTO CustomersOrderBackup2013 FROM Customers
LEFT JOIN Orders ON Customers.CustomerID=Orders

Tip: The SELECT INTO statement can also be used to create a new, empty table using the schema of another. Just add a WHERE clause that causes the query to return no data:

SELECT * INTO newtable FROM table1 WHERE 1=0;

The SQL INSERT INTO SELECT Statement

With SQL, you can copy information from one table into another.

The INSERT INTO SELECT statement copies data from one table and inserts it into an existing table.

The INSERT INTO SELECT statement selects data from one table and inserts it into an existing table. Any existing rows in the target table are unaffected.

SQL INSERT INTO SELECT Syntax

We can copy all columns from one table to another, existing table:

INSERT INTO table2
SELECT * FROM table1;

Or we can copy only the columns we want to into another, existing table:

INSERT INTO table2
(column_name(s))
SELECT column_name(s)
FROM table1;

Below is a selection from the "Customers" table:

CustomerID	CustomerName	ContactName	Address	City	PostalCode	Country
1	Alfreds Futterkiste	Maria Anders	Obere Str. 57	Berlin	12209	Germany
2	Ana Trujillo Emparedados y helados	Ana Trujillo	Avda. de la Constitución 2222	México D.F.	05021	Mexico
3	Antonio Moreno Taquería	Antonio Moreno	Mataderos 2312	México D.F.	05023	Mexico

And a selection from the "Suppliers" table:

SupplierID	SupplierName	ContactName	Address	City	Postal Code	Country	Phone
1	Exotic Liquid	Charlotte Cooper	49 Gilbert St.	Londona	EC1 4SD	UK	(171) 555-2222
2	New Orleans Cajun Delights	Shelley Burke	P.O. Box 78934	New Orleans	70117	USA	(100) 555-4822
3	Grandma Kelly's Homestead	Regina Murphy	707 Oxford Rd.	Ann Arbor	48104	USA	(313) 555-5735

SQL INSERT INTO SELECT Examples

Copy only a few columns from "Suppliers" into "Customers":

Example

INSERT INTO Customers (CustomerName, Country)
SELECT SupplierName, Country FROM Suppliers;

Copy only the German suppliers into "Customers":

Example

INSERT INTO Customers (CustomerName, Country)
SELECT SupplierName, Country FROM Suppliers
WHERE Country='Germany';

Other Commands:

The SQL SELECT TOP Clause

The SELECT TOP clause is used to specify the number of records to return.

The SELECT TOP clause can be very useful on large tables with thousands of records. Returning a large number of records can impact on performance.

Note: Not all database systems support the SELECT TOP clause.

SQL Server / MS Access Syntax

SELECT TOP number|percent column_name(s)
FROM table_name;

SQL SELECT TOP Equivalent in MySQL and Oracle

MySQL Syntax

SELECT column_name(s)
FROM table_name
LIMIT number;

Example

SELECT *
FROM Persons
LIMIT 5;

 

Oracle Syntax

SELECT column_name(s)
FROM table_name
WHERE ROWNUM <= number;

Example

SELECT *
FROM Persons
WHERE ROWNUM <=5;

Below is a selection from the "Customers" table:

CustomerID	CustomerName	ContactName	Address	City	PostalCode	Country
1	Alfreds Futterkiste	Maria Anders	Obere Str. 57	Berlin	12209	Germany
2	Ana Trujillo Emparedados y helados	Ana Trujillo	Avda. de la Constitución 2222	México D.F.	05021	Mexico
3	Antonio Moreno Taquería	Antonio Moreno	Mataderos 2312	México D.F.	05023	Mexico
4	Around the Horn	Thomas Hardy	120 Hanover Sq.	London	WA1 1DP	UK
5	Berglunds snabbköp	Christina Berglund	Berguvsvägen 8	Luleå	S-958 22	Sweden

SQL SELECT TOP Example

The following SQL statement selects the two first records from the "Customers" table:

Example

SELECT TOP 2 * FROM Customers;

SQL SELECT TOP PERCENT Example

The following SQL statement selects the first 50% of the records from the "Customers" table:

Example

SELECT TOP 50 PERCENT * FROM Customers;

The SQL LIKE Operator

The LIKE operator is used in a WHERE clause to search for a specified pattern in a column.

The LIKE operator is used to search for a specified pattern in a column.

SQL LIKE Syntax

SELECT column_name(s)
FROM table_name
WHERE column_name LIKE pattern;

Below is a selection from the "Customers" table:

CustomerID	CustomerName	ContactName	Address	City	PostalCode	Country
1	Alfreds Futterkiste	Maria Anders	Obere Str. 57	Berlin	12209	Germany
2	Ana Trujillo Emparedados y helados	Ana Trujillo	Avda. de la Constitución 2222	México D.F.	05021	Mexico
3	Antonio Moreno Taquería	Antonio Moreno	Mataderos 2312	México D.F.	05023	Mexico
4	Around the Horn	Thomas Hardy	120 Hanover Sq.	London	WA1 1DP	UK
5	Berglunds snabbköp	Christina Berglund	Berguvsvägen 8	Luleå	S-958 22	Sweden

SQL LIKE Operator Examples

The following SQL statement selects all customers with a City starting with the letter "s":

Example

SELECT * FROM Customers
WHERE City LIKE 's%';

Tip: The "%" sign is used to define wildcards (missing letters) both before and after the pattern. You will learn more about wildcards in the next chapter.

The following SQL statement selects all customers with a City ending with the letter "s":

Example

SELECT * FROM Customers
WHERE City LIKE '%s';

The following SQL statement selects all customers with a Country containing the pattern "land":

Example

SELECT * FROM Customers
WHERE Country LIKE '%land%';

Using the NOT keyword allows you to select records that does NOT match the pattern.

The following SQL statement selects all customers with a Country NOT containing the pattern "land":

Example

SELECT * FROM Customers
WHERE Country NOT LIKE '%land%';

SQL Wildcard Characters

A wildcard character can be used to substitute for any other character(s) in a string.

In SQL, wildcard characters are used with the SQL LIKE operator.

SQL wildcards are used to search for data within a table. 

With SQL, the wildcards are:

Wildcard	Description
%	A substitute for zero or more characters
_	A substitute for a single character
[charlist]	Sets and ranges of characters to match
[^charlist] or [!charlist]	Matches only a character NOT specified within the brackets

Below is a selection from the "Customers" table:

CustomerID	CustomerName	ContactName	Address	City	PostalCode	Country
1	Alfreds Futterkiste	Maria Anders	Obere Str. 57	Berlin	12209	Germany
2	Ana Trujillo Emparedados y helados	Ana Trujillo	Avda. de la Constitución 2222	México D.F.	05021	Mexico
3	Antonio Moreno Taquería	Antonio Moreno	Mataderos 2312	México D.F.	05023	Mexico
4	Around the Horn	Thomas Hardy	120 Hanover Sq.	London	WA1 1DP	UK
5	Berglunds snabbköp	Christina Berglund	Berguvsvägen 8	Luleå	S-958 22	Sweden

Using the SQL % Wildcard

The following SQL statement selects all customers with a City starting with "ber":

Example

SELECT * FROM Customers
WHERE City LIKE 'ber%';

The following SQL statement selects all customers with a City containing the pattern "es": 

Example

SELECT * FROM Customers
WHERE City LIKE '%es%';

Using the SQL _ Wildcard

The following SQL statement selects all customers with a City starting with any character, followed by "erlin":

Example

SELECT * FROM Customers
WHERE City LIKE '_erlin';

The following SQL statement selects all customers with a City starting with "L", followed by any character, followed by "n", followed by any character, followed by "on":

Example

SELECT * FROM Customers
WHERE City LIKE 'L_n_on';

Using the SQL [charlist] Wildcard

The following SQL statement selects all customers with a City starting with "b", "s", or "p":

Example

SELECT * FROM Customers
WHERE City LIKE '[bsp]%';

The following SQL statement selects all customers with a City starting with "a", "b", or "c":

Example

SELECT * FROM Customers
WHERE City LIKE '[a-c]%';

The following SQL statement selects all customers with a City NOT starting with "b", "s", or "p":

Example

SELECT * FROM Customers
WHERE City LIKE '[!bsp]%';

The SQL IN Operator

The IN operator allows you to specify multiple values in a WHERE clause.

SQL IN Syntax

SELECT column_name(s)
FROM table_name
WHERE column_name IN (value1,value2,...);

Below is a selection from the "Customers" table:

CustomerID	CustomerName	ContactName	Address	City	PostalCode	Country
1	Alfreds Futterkiste	Maria Anders	Obere Str. 57	Berlin	12209	Germany
2	Ana Trujillo Emparedados y helados	Ana Trujillo	Avda. de la Constitución 2222	México D.F.	05021	Mexico
3	Antonio Moreno Taquería	Antonio Moreno	Mataderos 2312	México D.F.	05023	Mexico
4	Around the Horn	Thomas Hardy	120 Hanover Sq.	London	WA1 1DP	UK
5	Berglunds snabbköp	Christina Berglund	Berguvsvägen 8	Luleå	S-958 22	Sweden

IN Operator Example

The following SQL statement selects all customers with a City of "Paris" or "London":

Example

SELECT * FROM Customers
WHERE City IN ('Paris','London');

The BETWEEN operator is used to select values within a range.

The SQL BETWEEN Operator

The BETWEEN operator selects values within a range. The values can be numbers, text, or dates.

SQL BETWEEN Syntax

SELECT column_name(s)
FROM table_name
WHERE column_name BETWEEN value1 AND value2;

Below is a selection from the "Products" table:

ProductID	ProductName	SupplierID	CategoryID	Unit	Price
1	Chais	1	1	10 boxes x 20 bags	18
2	Chang	1	1	24 - 12 oz bottles	19
3	Aniseed Syrup	1	2	12 - 550 ml bottles	10
4	Chef Anton's Cajun Seasoning	1	2	48 - 6 oz jars	22
5	Chef Anton's Gumbo Mix	1	2	36 boxes	21.35

BETWEEN Operator Example

The following SQL statement selects all products with a price BETWEEN 10 and 20:

Example

SELECT * FROM Products
WHERE Price BETWEEN 10 AND 20;

NOT BETWEEN Operator Example

To display the products outside the range of the previous example, use NOT BETWEEN:

Example

SELECT * FROM Products
WHERE Price NOT BETWEEN 10 AND 20;

BETWEEN Operator with IN Example

The following SQL statement selects all products with a price BETWEEN 10 and 20, but products with a CategoryID of 1,2, or 3 should not be displayed:

Example

SELECT * FROM Products
WHERE (Price BETWEEN 10 AND 20)
AND NOT CategoryID IN (1,2,3);

BETWEEN Operator with Text Value Example

The following SQL statement selects all products with a ProductName beginning with any of the letter BETWEEN 'C' and 'M':

Example

SELECT * FROM Products
WHERE ProductName BETWEEN 'C' AND 'M';

NOT BETWEEN Operator with Text Value Example

The following SQL statement selects all products with a ProductName beginning with any of the letter NOT BETWEEN 'C' and 'M':

Example

SELECT * FROM Products
WHERE ProductName NOT BETWEEN 'C' AND 'M';

Sample Table

Below is a selection from the "Orders" table:

OrderID	CustomerID	EmployeeID	OrderDate	ShipperID
10248	90	5	7/4/1996	3
10249	81	6	7/5/1996	1
10250	34	4	7/8/1996	2
10251	84	3	7/9/1996	1
10252	76	4	7/10/1996	2

BETWEEN Operator with Date Value Example

The following SQL statement selects all orders with an OrderDate BETWEEN '04-July-1996' and '09-July-1996':

Example

SELECT * FROM Orders
WHERE OrderDate BETWEEN #07/04/1996# AND #07/09/1996#;

Notice that the BETWEEN operator can produce different result in different databases!
In some databases, BETWEEN selects fields that are between and excluding the test values.
In other databases, BETWEEN selects fields that are between and including the test values.
And in other databases, BETWEEN selects fields between the test values, including the first test value and excluding the last test value.

Therefore: Check how your database treats the BETWEEN operator!

SQL Aliases

SQL aliases are used to temporarily rename a table or a column heading.

SQL aliases are used to give a database table, or a column in a table, a temporary name.

Basically aliases are created to make column names more readable.

SQL Alias Syntax for Columns

SELECT column_name AS alias_name
FROM table_name;

SQL Alias Syntax for Tables

SELECT column_name(s)
FROM table_name AS alias_name;

Below is a selection from the "Customers" table:

CustomerID	CustomerName	ContactName	Address	City	PostalCode	Country
2	Ana Trujillo Emparedados y helados	Ana Trujillo	Avda. de la Constitución 2222	México D.F.	05021	Mexico
3	Antonio Moreno Taquería	Antonio Moreno	Mataderos 2312	México D.F.	05023	Mexico
4	Around the Horn	Thomas Hardy	120 Hanover Sq.	London	WA1 1DP	UK

And a selection from the "Orders" table:

OrderID	CustomerID	EmployeeID	OrderDate	ShipperID
10354	58	8	1996-11-14	3
10355	4	6	1996-11-15	1
10356	86	6	1996-11-18	2

Alias Example for Table Columns

The following SQL statement specifies two aliases, one for the CustomerName column and one for the ContactName column. Tip: It require double quotation marks or square brackets if the column name contains spaces:

Example

SELECT CustomerName AS Customer, ContactName AS [Contact Person]
FROM Customers;

In the following SQL statement we combine four columns (Address, City, PostalCode, and Country) and create an alias named "Address":

Example

SELECT CustomerName, Address+', '+City+', '+PostalCode+', '+Country AS Address FROM Customers;

Note: To get the SQL statement above to work in MySQL use the following:

SELECT CustomerName, CONCAT(Address,', ',City,', ',PostalCode,', ',Country) AS Address FROM Customers;

 

Alias Example for Tables

The following SQL statement selects all the orders from the customer with CustomerID=4 (Around the Horn). We use the "Customers" and "Orders" tables, and give them the table aliases of "c" and "o" respectively (Here we have used aliases to make the SQL shorter):

Example

SELECT o.OrderID, o.OrderDate, c.CustomerName
FROM Customers AS c, Orders AS o
WHERE c.CustomerName="Around the Horn" AND c.CustomerID=o.CustomerID;

The same SQL statement without aliases:

Example

SELECT Orders.OrderID, Orders.OrderDate, Customers.CustomerName
FROM Customers, Orders
WHERE Customers.CustomerName="Around the Horn" AND Customers.CustomerID=Orders.CustomerID;

Aliases can be useful when:

• There are more than one table involved in a query
• Functions are used in the query
• Column names are big or not very readable
• Two or more columns are combined together

The SQL UNION Operator

The SQL UNION operator combines the result of two or more SELECT statements.

The UNION operator is used to combine the result-set of two or more SELECT statements.

Notice that each SELECT statement within the UNION must have the same number of columns. The columns must also have similar data types. Also, the columns in each SELECT statement must be in the same order.

SQL UNION Syntax

SELECT column_name(s) FROM table1
UNION
SELECT column_name(s) FROM table2;

Note: The UNION operator selects only distinct values by default. To allow duplicate values, use the ALL keyword with UNION.

SQL UNION ALL Syntax

SELECT column_name(s) FROM table1
UNION ALL
SELECT column_name(s) FROM table2;

PS: The column names in the result-set of a UNION are usually equal to the column names in the first SELECT statement in the UNION.

Below is a selection from the "Customers" table:

CustomerID	CustomerName	ContactName	Address	City	PostalCode	Country
1	Alfreds Futterkiste	Maria Anders	Obere Str. 57	Berlin	12209	Germany
2	Ana Trujillo Emparedados y helados	Ana Trujillo	Avda. de la Constitución 2222	México D.F.	05021	Mexico
3	Antonio Moreno Taquería	Antonio Moreno	Mataderos 2312	México D.F.	05023	Mexico

And a selection from the "Suppliers" table:

SupplierID	SupplierName	ContactName	Address	City	PostalCode	Country
1	Exotic Liquid	Charlotte Cooper	49 Gilbert St.	Londona	EC1 4SD	UK
2	New Orleans Cajun Delights	Shelley Burke	P.O. Box 78934	New Orleans	70117	USA
3	Grandma Kelly's Homestead	Regina Murphy	707 Oxford Rd.	Ann Arbor	48104	USA

SQL UNION Example

The following SQL statement selects all the different cities (only distinct values) from the "Customers" and the "Suppliers" tables:

Example

SELECT City FROM Customers
UNION
SELECT City FROM Suppliers
ORDER BY City;

Note: UNION cannot be used to list ALL cities from the two tables. If several customers and suppliers share the same city, each city will only be listed once. UNION selects only distinct values. Use UNION ALL to also select duplicate values!

SQL UNION ALL Example

The following SQL statement uses UNION ALL to select all (duplicate values also) cities from the "Customers" and "Suppliers" tables:

Example

SELECT City FROM Customers
UNION ALL
SELECT City FROM Suppliers
ORDER BY City;

SQL UNION ALL With WHERE

The following SQL statement uses UNION ALL to select all (duplicate values also) German cities from the "Customers" and "Suppliers" tables:

Example

SELECT City, Country FROM Customers
WHERE Country='Germany'
UNION ALL
SELECT City, Country FROM Suppliers
WHERE Country='Germany'
ORDER BY City;

AUTO INCREMENT a Field

Auto-increment allows a unique number to be generated when a new record is inserted into a table.

Very often we would like the value of the primary key field to be created automatically every time a new record is inserted.

We would like to create an auto-increment field in a table.

Syntax for MySQL

The following SQL statement defines the "ID" column to be an auto-increment primary key field in the "Persons" table:

CREATE TABLE Persons
(
ID int NOT NULL AUTO_INCREMENT,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Address varchar(255),
City varchar(255),
PRIMARY KEY (ID)
)

MySQL uses the AUTO_INCREMENT keyword to perform an auto-increment feature.

By default, the starting value for AUTO_INCREMENT is 1, and it will increment by 1 for each new record.

To let the AUTO_INCREMENT sequence start with another value, use the following SQL statement:

ALTER TABLE Persons AUTO_INCREMENT=100

To insert a new record into the "Persons" table, we will NOT have to specify a value for the "ID" column (a unique value will be added automatically):

INSERT INTO Persons (FirstName,LastName) VALUES ('Lars','Monsen')

The SQL statement above would insert a new record into the "Persons" table. The "ID" column would be assigned a unique value. The "FirstName" column would be set to "Lars" and the "LastName" column would be set to "Monsen".

Syntax for SQL Server

The following SQL statement defines the "ID" column to be an auto-increment primary key field in the "Persons" table:

CREATE TABLE Persons
(
ID int IDENTITY(1,1) PRIMARY KEY,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Address varchar(255),
City varchar(255)
)

The MS SQL Server uses the IDENTITY keyword to perform an auto-increment feature.

In the example above, the starting value for IDENTITY is 1, and it will increment by 1 for each new record.

Tip: To specify that the "ID" column should start at value 10 and increment by 5, change it to IDENTITY(10,5).

To insert a new record into the "Persons" table, we will NOT have to specify a value for the "ID" column (a unique value will be added automatically):

INSERT INTO Persons (FirstName,LastName) VALUES ('Lars','Monsen')

The SQL statement above would insert a new record into the "Persons" table. The "ID" column would be assigned a unique value. The "FirstName" column would be set to "Lars" and the "LastName" column would be set to "Monsen".

Syntax for Access

The following SQL statement defines the "ID" column to be an auto-increment primary key field in the "Persons" table:

CREATE TABLE Persons
(
ID Integer PRIMARY KEY AUTOINCREMENT,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Address varchar(255),
City varchar(255)
)

The MS Access uses the AUTOINCREMENT keyword to perform an auto-increment feature.

By default, the starting value for AUTOINCREMENT is 1, and it will increment by 1 for each new record.

Tip: To specify that the "ID" column should start at value 10 and increment by 5, change the autoincrement to AUTOINCREMENT(10,5).

To insert a new record into the "Persons" table, we will NOT have to specify a value for the "ID" column (a unique value will be added automatically):

INSERT INTO Persons (FirstName,LastName) VALUES ('Lars','Monsen')

The SQL statement above would insert a new record into the "Persons" table. The "P_Id" column would be assigned a unique value. The "FirstName" column would be set to "Lars" and the "LastName" column would be set to "Monsen".

Syntax for Oracle

In Oracle the code is a little bit more tricky.

You will have to create an auto-increment field with the sequence object (this object generates a number sequence).

Use the following CREATE SEQUENCE syntax:

CREATE SEQUENCE seq_person
MINVALUE 1
START WITH 1
INCREMENT BY 1
CACHE 10

The code above creates a sequence object called seq_person, that starts with 1 and will increment by 1. It will also cache up to 10 values for performance. The cache option specifies how many sequence values will be stored in memory for faster access.

To insert a new record into the "Persons" table, we will have to use the nextval function (this function retrieves the next value from seq_person sequence):

INSERT INTO Persons (ID,FirstName,LastName) VALUES (seq_person.nextval,'Lars','Monsen')

The SQL statement above would insert a new record into the "Persons" table. The "ID" column would be assigned the next number from the seq_person sequence. The "FirstName" column would be set to "Lars" and the "LastName" column would be set to "Monsen".