SQL WHERE Clause

The SQL WHERE Clause is used to restrict the number of rows (or records) returned by the SQL SELECT Statement. The SELECT Statement will return the records only If the condition specified after the WHERE keyword is TRUE.

For instance we want to order shoes in the Amazon website. When we type shoes in search bar it will show thousands of shoes but To select required shoe we have to use filters such as price range between 2000 to 2500 and brand = Nike or Adidas. If we use the above filters it will only display the shoes that are matching the above requirements so that we can select easily. Let us see what happens internally (mean T-SQL Query against the Amazon Database). It will go something like this:

SQL WHERE Clause Syntax

The SELECT Statement with WHERE Clause in SQL Server can be written as:

• Columns: It allows us to choose the number of columns from the tables. It may be One or more.
• Source: One or more tables present in the Database. SQL JOINS are used to join multiple table.
• Conditions: Here we have to provide the filters or conditions. If the condition is TRUE then only SELECT Statement will return the records.

SQL WHERE Clause Examples

In this article we will show you, How to use the WHERE Clause to filter the data before extracting it using SELECT statement. We are going to use the below shown data to explain the WHERE Clause in SQL Server with example.

Using Single Condition in SQL WHERE Clause

In this example we are going to use single condition in the WHERE Clause.

T-SQL CODE

Above statement will retrieve above mentioned records where the occupation is exactly equal to Professional

OUTPUT

Using Multiple Conditions in SQL WHERE Clause

In this example we are going to use Multiple Conditions in the WHERE Clause.

T-SQL CODE

Above statement will retrieve above mentioned records where the occupation is equal to either Professional or Management.

OUTPUT

Using General Expressions in SQL WHERE Clause

Instead of testing conditions against Column Names, WHERE Clause allows us to test general conditions. For instance below condition is checking 1 is exactly equal to 2, which is False so SELECT statement will not return any record.

T-SQL CODE

OUTPUT

Let us change the condition (1 = 1). Here the condition is TRUE so it is displaying all the records present in the Customers Table

NOTE: Do not use ALIAS Column Names in the WHERE Condition because WHERE Clause will execute first and then SELECT Statement will select the Columns. So, WHERE Clause does not understand the ALIAS Columns declared in the SELECT Statement.

Thank You for Visiting Our Blog