SQL BASICS

1. SQL Syntax
2. SQL SELECT Statement
3. SQL SELECT DISTINCT Statement
4. SQL WHERE Clause
5. SQL AND, OR and NOT Operators
6. SQL ORDER BY Keyword
7. SQL INSERT INTO Statement
8. SQL NULL Values
9. SQL UPDATE Statement
10. SQL DELETE Statement
11. SQL TOP, LIMIT, FETCH FIRST or ROWNUM Clause
12. SQL MIN() and MAX() Functions
13. SQL COUNT(), AVG() and SUM() Functions
14. SQL LIKE Operator
15. SQL Wildcards
16. SQL IN Operator
17. SQL BETWEEN Operator
18. SQL Aliases

B01. SQL Syntax

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.

In this tutorial we will use the well-known Northwind sample database (included in MS Access and MS SQL Server).

Below is a selection from the "Customers" table:

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

SQL Statements

Most of the actions you need to perform on a database are done with SQL statements.

The following SQL statement selects all the records in the "Customers" table:

Example

SELECT * FROM Customers;

Keep in Mind That...

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

In this tutorial we will write all SQL keywords in upper-case.

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

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

B02. SQL SELECT Statement

The SQL SELECT Statement

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

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

SELECT Syntax

SELECT column1, column2, ...
FROM table_name;

Here, column1, column2, ... are the field names of the table you want to select data from. If you want to select all the fields available in the table, use the following syntax:

SELECT * FROM table_name;

Demo Database

Below is a selection from the "Customers" table in the Northwind sample database:

SELECT Column Example

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

Example

SELECT CustomerName, City FROM Customers;

B03. SQL SELECT DISTINCT Statement

The SQL SELECT DISTINCT Statement

The SELECT DISTINCT statement is used to return only distinct (different) values.

Inside a table, a column often contains many duplicate values; and sometimes you only want to list the different (distinct) values.

SELECT DISTINCT Syntax

SELECT DISTINCT column1, column2, ...
FROM table_name;

Demo Database

Below is a selection from the "Customers" table in the Northwind sample database:

SELECT Example Without DISTINCT

The following SQL statement selects all (including the duplicates) values from the "Country" column in the "Customers" table:

Example

SELECT Country FROM Customers;

Now, let us use the SELECT DISTINCT statement and see the result.

SELECT DISTINCT Examples

The following SQL statement selects only the DISTINCT values from the "Country" column in the "Customers" table:

Example

SELECT DISTINCT Country FROM Customers;

The following SQL statement lists the number of different (distinct) customer countries:

Example

SELECT COUNT(DISTINCT Country) FROM Customers;

Note: The example above will not work in Firefox! Because COUNT(DISTINCT column_name) is not supported in Microsoft Access databases. Firefox is using Microsoft Access in our examples.

Here is the workaround for MS Access:

Example

SELECT Count(*) AS DistinctCountries
FROM (SELECT DISTINCT Country FROM Customers);

B04. SQL WHERE Clause

The SQL WHERE Clause

The WHERE clause is used to filter records.

It is used to extract only those records that fulfill a specified condition.

WHERE Syntax

SELECT column1, column2, ...
FROM table_name
WHERE condition;

Note: The WHERE clause is not only used in SELECT statements, it is also used in UPDATE, DELETE, etc.!

Demo Database

Below is a selection from the "Customers" table in the Northwind sample database:

WHERE Clause Example

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

Example

SELECT * FROM Customers
WHERE Country='Mexico';

Try it Yourself »

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;

Try it Yourself »

Operators in The WHERE Clause

The following operators can be used in the WHERE clause:

SELECT * FROM Customers
  = ;

B05. SQL AND, OR and NOT Operators

The SQL AND, OR and NOT Operators

The WHERE clause can be combined with AND, OR, and NOT operators.

The AND and OR operators are used to filter records based on more than one condition:

• The AND operator displays a record if all the conditions separated by AND are TRUE.
• The OR operator displays a record if any of the conditions separated by OR is TRUE.

The NOT operator displays a record if the condition(s) is NOT TRUE.

AND Syntax

SELECT column1, column2, ...
FROM table_name
WHERE condition1 AND condition2 AND condition3 ...;

OR Syntax

SELECT column1, column2, ...
FROM table_name
WHERE condition1 OR condition2 OR condition3 ...;

NOT Syntax

SELECT column1, column2, ...
FROM table_name
WHERE NOT condition;

Demo Database

The table below shows the complete "Customers" table from the Northwind sample database:

AND Example

The following SQL statement selects all fields from "Customers" where country is "Germany" AND city is "Berlin":

Example

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

Try it Yourself »

OR Example

The following SQL statement selects all fields from "Customers" where city is "Berlin" OR "München":

Example

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

The following SQL statement selects all fields from "Customers" where country is "Germany" OR "Spain":

Example

SELECT * FROM Customers
WHERE Country='Germany' OR Country='Spain';

NOT Example

The following SQL statement selects all fields from "Customers" where country is NOT "Germany":

Example

SELECT * FROM Customers
WHERE NOT Country='Germany';

Combining AND, OR and NOT

You can also combine the AND, OR and NOT operators.

The following SQL statement selects all fields from "Customers" where country is "Germany" AND city must be "Berlin" OR "München" (use parenthesis to form complex expressions):

Example

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

The following SQL statement selects all fields from "Customers" where country is NOT "Germany" and NOT "USA":

Example

SELECT * FROM Customers
WHERE NOT Country='Germany' AND NOT Country='USA';

 * FROM Customers
 City = 'Berlin'
  = 12209;

B06. SQL ORDER BY Keyword

The SQL ORDER BY Keyword

The ORDER BY keyword is used to sort the result-set in ascending or descending order.

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

ORDER BY Syntax

SELECT column1, column2, ...
FROM table_name
ORDER BY column1, column2, ... ASC|DESC;

Demo Database

Below is a selection from the "Customers" table in the Northwind sample database:

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;

B07. SQL INSERT INTO Statement

The SQL INSERT INTO Statement

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

INSERT INTO Syntax

It is possible to write the INSERT INTO statement in two ways:

1. Specify both the column names and the values to be inserted:

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

2. If you are adding values for all the columns of the table, you do not need to specify the column names in the SQL query. However, make sure the order of the values is in the same order as the columns in the table. Here, the INSERT INTO syntax would be as follows:

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

Demo Database

Below is a selection from the "Customers" table in the Northwind sample database:

INSERT INTO Example

The following SQL statement inserts a new record in the "Customers" table:

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:

Did you notice that we did not insert any number into the CustomerID field?
The CustomerID column is an auto-increment field and will be generated automatically when a new record is inserted into the table.

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 record, but only insert data in the "CustomerName", "City", and "Country" columns (CustomerID will 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:

 Customers 
CustomerName, 
Address, 
City, 
PostalCode,
Country
 
'Hekkan Burger',
'Gateveien 15',
'Sandnes',
'4306',
'Norway';

B08. SQL NULL Values

What is a NULL Value?

A field with a NULL value is a field with no value.

If a field in a table is optional, it is possible to insert a new record or update a record without adding a value to this field. Then, the field will be saved with a NULL value.

Note: A NULL value is different from a zero value or a field that contains spaces. A field with a NULL value is one that has been left blank during record creation!

How to Test for NULL Values?

It is not possible to test for NULL values with comparison operators, such as =, <, or <>.

We will have to use the IS NULL and IS NOT NULL operators instead.

IS NULL Syntax

SELECT column_names
FROM table_name
WHERE column_name IS NULL;

IS NOT NULL Syntax

SELECT column_names
FROM table_name
WHERE column_name IS NOT NULL;

Demo Database

Below is a selection from the "Customers" table in the Northwind sample database:

The IS NULL Operator

The IS NULL operator is used to test for empty values (NULL values).

The following SQL lists all customers with a NULL value in the "Address" field:

Example

SELECT CustomerName, ContactName, Address
FROM Customers
WHERE Address IS NULL;

Tip: Always use IS NULL to look for NULL values.

The IS NOT NULL Operator

The IS NOT NULL operator is used to test for non-empty values (NOT NULL values).

The following SQL lists all customers with a value in the "Address" field:

Example

SELECT CustomerName, ContactName, Address
FROM Customers
WHERE Address IS NOT NULL;

SELECT * FROM Customers
WHERE   ;

B09. SQL UPDATE Statement

The SQL UPDATE Statement

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

UPDATE Syntax

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

Note: Be careful when updating records in a table! Notice the WHERE clause in the UPDATE statement. The WHERE clause specifies which record(s) that should be updated. If you omit the WHERE clause, all records in the table will be updated!

Demo Database

Below is a selection from the "Customers" table in the Northwind sample database:

UPDATE Table

The following SQL statement updates the first customer (CustomerID = 1) with a new contact person and a new city.

Example

UPDATE Customers
SET ContactName = 'Alfred Schmidt', City= 'Frankfurt'
WHERE CustomerID = 1;

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

UPDATE Multiple Records

It is the WHERE clause that determines how many records will be updated.

The following SQL statement will update the ContactName to "Juan" for all records where country is "Mexico":

Example

UPDATE Customers
SET ContactName='Juan'
WHERE Country='Mexico';

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

Update Warning!

Be careful when updating records. If you omit the WHERE clause, ALL records will be updated!

Example

UPDATE Customers
SET ContactName='Juan';

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

 Customers
 City = 'Oslo';

B10. SQL DELETE Statement

The SQL DELETE Statement

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

DELETE Syntax

DELETE FROM table_name WHERE condition;

Note: Be careful when deleting records in a table! Notice the WHERE clause in the DELETE statement. The WHERE clause specifies which record(s) should be deleted. If you omit the WHERE clause, all records in the table will be deleted!

Demo Database

Below is a selection from the "Customers" table in the Northwind sample database:

SQL DELETE Example

The following SQL statement deletes the customer "Alfreds Futterkiste" from the "Customers" table:

Example

DELETE FROM Customers WHERE CustomerName='Alfreds Futterkiste';

The "Customers" table will now look like this:

Delete All Records

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;

The following SQL statement deletes all rows in the "Customers" table, without deleting the table:

Example

DELETE FROM Customers;

 Customers
 Country = 'Norway';

B11. SQL TOP, LIMIT, FETCH FIRST or ROWNUM Clause

The SQL SELECT TOP Clause

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

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

Note: Not all database systems support the SELECT TOP clause. MySQL supports the LIMIT clause to select a limited number of records, while Oracle uses FETCH FIRST n ROWS ONLY and ROWNUM.

SQL Server / MS Access Syntax:

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

MySQL Syntax:

SELECT column_name(s)
FROM table_name
WHERE condition
LIMIT number;

Oracle 12 Syntax:

SELECT column_name(s)
FROM table_name
ORDER BY column_name(s)
FETCH FIRST number ROWS ONLY;

Older Oracle Syntax:

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

Older Oracle Syntax (with ORDER BY):

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

Demo Database

Below is a selection from the "Customers" table in the Northwind sample database:

SQL TOP, LIMIT and FETCH FIRST Examples

The following SQL statement selects the first three records from the "Customers" table (for SQL Server/MS Access):

Example

SELECT TOP 3 * FROM Customers;

The following SQL statement shows the equivalent example for MySQL:

Example

SELECT * FROM Customers
LIMIT 3;

The following SQL statement shows the equivalent example for Oracle:

Example

SELECT * FROM Customers
FETCH FIRST 3 ROWS ONLY;

SQL TOP PERCENT Example

The following SQL statement selects the first 50% of the records from the "Customers" table (for SQL Server/MS Access):

Example

SELECT TOP 50 PERCENT * FROM Customers;

The following SQL statement shows the equivalent example for Oracle:

Example

SELECT * FROM Customers
FETCH FIRST 50 PERCENT ROWS ONLY;

ADD a WHERE CLAUSE

The following SQL statement selects the first three records from the "Customers" table, where the country is "Germany" (for SQL Server/MS Access):

Example

SELECT TOP 3 * FROM Customers
WHERE Country='Germany';

The following SQL statement shows the equivalent example for MySQL:

Example

SELECT * FROM Customers
WHERE Country='Germany'
LIMIT 3;

The following SQL statement shows the equivalent example for Oracle:

Example

SELECT * FROM Customers
WHERE Country='Germany'
FETCH FIRST 3 ROWS ONLY;

B12. SQL MIN() and MAX() Functions

The SQL MIN() and MAX() Functions

The MIN() function returns the smallest value of the selected column.

The MAX() function returns the largest value of the selected column.

MIN() Syntax

SELECT MIN(column_name)
FROM table_name
WHERE condition;

MAX() Syntax

SELECT MAX(column_name)
FROM table_name
WHERE condition;

Demo Database

Below is a selection from the "Products" table in the Northwind sample database:

MIN() Example

The following SQL statement finds the price of the cheapest product:

Example

SELECT MIN(Price) AS SmallestPrice
FROM Products;

MAX() Example

The following SQL statement finds the price of the most expensive product:

Example

SELECT MAX(Price) AS LargestPrice
FROM Products;

SELECT 
FROM Products;

B13. SQL COUNT(), AVG() and SUM() Functions

The SQL COUNT(), AVG() and SUM() Functions

The COUNT() function returns the number of rows that matches a specified criterion.

COUNT() Syntax

SELECT COUNT(column_name)
FROM table_name
WHERE condition;

The AVG() function returns the average value of a numeric column. 

AVG() Syntax

SELECT AVG(column_name)
FROM table_name
WHERE condition;

The SUM() function returns the total sum of a numeric column. 

SUM() Syntax

SELECT SUM(column_name)
FROM table_name
WHERE condition;

Demo Database

Below is a selection from the "Products" table in the Northwind sample database:

COUNT() Example

The following SQL statement finds the number of products:

Example

SELECT COUNT(ProductID)
FROM Products;

Note: NULL values are not counted.

AVG() Example

The following SQL statement finds the average price of all products:

Example

SELECT AVG(Price)
FROM Products;

Note: NULL values are ignored.

Demo Database

Below is a selection from the "OrderDetails" table in the Northwind sample database:

SUM() Example

The following SQL statement finds the sum of the "Quantity" fields in the "OrderDetails" table:

Example

SELECT SUM(Quantity)
FROM OrderDetails;

Note: NULL values are ignored.

SELECT (*)
FROM Products
 Price = 18;

B14. SQL LIKE Operator

The SQL LIKE Operator

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

There are two wildcards often used in conjunction with the LIKE operator:

•  The percent sign (%) represents zero, one, or multiple characters
•  The underscore sign (_) represents one, single character

Note: MS Access uses an asterisk (*) instead of the percent sign (%), and a question mark (?) instead of the underscore (_).

The percent sign and the underscore can also be used in combinations!

LIKE Syntax

SELECT column1, column2, ...
FROM table_name
WHERE columnN LIKE pattern;

Tip: You can also combine any number of conditions using AND or OR operators.

Here are some examples showing different LIKE operators with '%' and '_' wildcards:

Demo Database

The table below shows the complete "Customers" table from the Northwind sample database:

SQL LIKE Examples

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

Example

SELECT * FROM Customers
WHERE CustomerName LIKE 'a%';

The following SQL statement selects all customers with a CustomerName ending with "a":

Example

SELECT * FROM Customers
WHERE CustomerName LIKE '%a';

The following SQL statement selects all customers with a CustomerName that have "or" in any position:

Example

SELECT * FROM Customers
WHERE CustomerName LIKE '%or%';

The following SQL statement selects all customers with a CustomerName that have "r" in the second position:

Example

SELECT * FROM Customers
WHERE CustomerName LIKE '_r%';

The following SQL statement selects all customers with a CustomerName that starts with "a" and are at least 3 characters in length:

Example

SELECT * FROM Customers
WHERE CustomerName LIKE 'a__%';

The following SQL statement selects all customers with a ContactName that starts with "a" and ends with "o":

Example

SELECT * FROM Customers
WHERE ContactName LIKE 'a%o';

The following SQL statement selects all customers with a CustomerName that does NOT start with "a":

Example

SELECT * FROM Customers
WHERE CustomerName NOT LIKE 'a%';

SELECT * FROM Customers
;

B15. SQL Wildcards

SQL Wildcard Characters

A wildcard character is used to substitute one or more characters in a string.

Wildcard characters are used with the LIKE operator. The LIKE operator is used in a WHERE clause to search for a specified pattern in a column.

Wildcard Characters in MS Access

Wildcard Characters in SQL Server

All the wildcards can also be used in combinations!

Here are some examples showing different LIKE operators with '%' and '_' wildcards:

Demo Database

The table below shows the complete "Customers" table from the Northwind sample database:

Using the % 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 _ Wildcard

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

Example

SELECT * FROM Customers
WHERE City LIKE '_ondon';

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 [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]%';

Using the [!charlist] Wildcard

The two following SQL statements select all customers with a City NOT starting with "b", "s", or "p":

Example

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

Or:

Example

SELECT * FROM Customers
WHERE City NOT LIKE '[bsp]%';

SELECT * FROM Customers
WHERE City LIKE '%';

B16. SQL IN Operator

The SQL IN Operator

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

The IN operator is a shorthand for multiple OR conditions.

IN Syntax

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

or:

SELECT column_name(s)
FROM table_name
WHERE column_name IN (SELECT STATEMENT);

Demo Database

The table below shows the complete "Customers" table from the Northwind sample database:

IN Operator Examples

The following SQL statement selects all customers that are located in "Germany", "France" or "UK":

Example

SELECT * FROM Customers
WHERE Country IN ('Germany', 'France', 'UK');

The following SQL statement selects all customers that are NOT located in "Germany", "France" or "UK":

Example

SELECT * FROM Customers
WHERE Country NOT IN ('Germany', 'France', 'UK');

The following SQL statement selects all customers that are from the same countries as the suppliers:

Example

SELECT * FROM Customers
WHERE Country IN (SELECT Country FROM Suppliers);

SELECT * FROM Customers
  'France';

B17. SQL BETWEEN Operator

The SQL BETWEEN Operator

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

The BETWEEN operator is inclusive: begin and end values are included. 

BETWEEN Syntax

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

Demo Database

Below is a selection from the "Products" table in the Northwind sample database:

BETWEEN 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;

Try it Yourself »

NOT BETWEEN 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 with IN Example

The following SQL statement selects all products with a price between 10 and 20. In addition; do not show products with a CategoryID of 1,2, or 3:

Example

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

BETWEEN Text Values Example

The following SQL statement selects all products with a ProductName between Carnarvon Tigers and Mozzarella di Giovanni:

Example

SELECT * FROM Products
WHERE ProductName BETWEEN 'Carnarvon Tigers' AND 'Mozzarella di Giovanni'
ORDER BY ProductName;

The following SQL statement selects all products with a ProductName between Carnarvon Tigers and Chef Anton's Cajun Seasoning:

Example

SELECT * FROM Products
WHERE ProductName BETWEEN "Carnarvon Tigers" AND "Chef Anton's Cajun Seasoning"
ORDER BY ProductName;

NOT BETWEEN Text Values Example

The following SQL statement selects all products with a ProductName not between Carnarvon Tigers and Mozzarella di Giovanni:

Example

SELECT * FROM Products
WHERE ProductName NOT BETWEEN 'Carnarvon Tigers' AND 'Mozzarella di Giovanni'
ORDER BY ProductName;

Sample Table

Below is a selection from the "Orders" table in the Northwind sample database:

BETWEEN Dates Example

The following SQL statement selects all orders with an OrderDate between '01-July-1996' and '31-July-1996':

Example

SELECT * FROM Orders
WHERE OrderDate BETWEEN #07/01/1996# AND #07/31/1996#;

OR:

Example

SELECT * FROM Orders
WHERE OrderDate BETWEEN '1996-07-01' AND '1996-07-31';

SELECT * FROM Products
WHERE Price ;

B18. SQL Aliases

SQL Aliases

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

Aliases are often used to make column names more readable.

An alias only exists for the duration of that query.

An alias is created with the AS keyword.

Alias Column Syntax

SELECT column_name AS alias_name
FROM table_name;

Alias Table Syntax

SELECT column_name(s)
FROM table_name AS alias_name;

Demo Database

In this tutorial we will use the well-known Northwind sample database.

Below is a selection from the "Customers" table:

And a selection from the "Orders" table:

Alias for Columns Examples

The following SQL statement creates two aliases, one for the CustomerID column and one for the CustomerName column:

Example

SELECT CustomerID AS ID, CustomerName AS Customer
FROM Customers;

The following SQL statement creates two aliases, one for the CustomerName column and one for the ContactName column. Note: It requires double quotation marks or square brackets if the alias name contains spaces:

Example

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

The following SQL statement creates an alias named "Address" that combine four columns (Address, PostalCode, City and Country):

Example

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

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

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

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

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

Alias for Tables Example

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 use 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 following SQL statement is the same as above, but 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

SELECT CustomerName,
Address,
PostalCode 
FROM Customers;