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SQL WHERE Clause

In this tutorial you'll learn how to select specific records from a table using SQL.

Selecting Record Based on Condition

In the previous chapter we've learnt how to fetch all the records form a table or table columns. But, in real world scenario we generally need to select, update or delete only those records which fulfill certain condition like users who belongs to a certain age group, or country, etc.

The WHERE clause is used with the SELECT, UPDATE, and DELETE. However, you'll see the use of this clause with other statements in upcoming chapters.

Syntax

The WHERE clause is used with SELECT statement to extract only those records that fulfill specified conditions. The basic syntax can be given with:

SELECT column_list FROM table_name WHERE condition;

Here, column_list are the names of columns/fields like name, age, country etc. of a database table whose values you want to fetch. However, if you want to fetch the values of all the columns available in a table, you can use the following syntax:

SELECT * FROM table_name WHERE condition;

Now, let's check out some examples that demonstrate how it actually works.

Suppose we've a table called employees in our database with the following records:

+--------+--------------+------------+--------+---------+
| emp_id | emp_name     | hire_date  | salary | dept_id |
+--------+--------------+------------+--------+---------+
|      1 | Ethan Hunt   | 2001-05-01 |   5000 |       4 |
|      2 | Tony Montana | 2002-07-15 |   6500 |       1 |
|      3 | Sarah Connor | 2005-10-18 |   8000 |       5 |
|      4 | Rick Deckard | 2007-01-03 |   7200 |       3 |
|      5 | Martin Blank | 2008-06-24 |   5600 |    NULL |
+--------+--------------+------------+--------+---------+

Filter Records with WHERE Clause

The following SQL statement will returns all the employees from the employees table, whose salary is greater than 7000. The WHERE clause simply filtered out the unwanted data.

  • SELECT * FROM employees
  • WHERE salary > 7000;

After execution, the output will look something like this:

+--------+--------------+------------+--------+---------+
| emp_id | emp_name     | hire_date  | salary | dept_id |
+--------+--------------+------------+--------+---------+
|      3 | Sarah Connor | 2005-10-18 |   8000 |       5 |
|      4 | Rick Deckard | 2007-01-03 |   7200 |       3 |
+--------+--------------+------------+--------+---------+

As you can see the output contains only those employees whose salary is greater than 7000. Similarly, you can fetch records from specific columns, like this:

  • SELECT emp_id, emp_name, hire_date, salary
  • FROM employees
  • WHERE salary > 7000;

After executing the above statement, you'll get the output something like this:

+--------+--------------+------------+--------+
| emp_id | emp_name     | hire_date  | salary |
+--------+--------------+------------+--------+
|      3 | Sarah Connor | 2005-10-18 |   8000 |
|      4 | Rick Deckard | 2007-01-03 |   7200 |
+--------+--------------+------------+--------+

The following statement will fetch the records of an employee whose employee id is 2.

  • SELECT * FROM employees
  • WHERE emp_id = 2;

This statement will produce the following output:

+--------+--------------+------------+--------+---------+
| emp_id | emp_name     | hire_date  | salary | dept_id |
+--------+--------------+------------+--------+---------+
|      2 | Tony Montana | 2002-07-15 |   6500 |       1 |
+--------+--------------+------------+--------+---------+

This time we got only one row in the output, because emp_id is unique for every employee.

Note: To populate a text based table field you need to enclose the string in single quotes. However if your string itself contains quotes you should escape it with backslash like 'Let\'s go'. Numeric value doesn't require any quotes.


Operators Allowed in WHERE Clause

SQL supports a number of different operators that can be used in WHERE clause, the most important ones are summarized in the following table.

Operator Description Example
= Equal WHERE id = 2
> Greater than WHERE age > 30
< Less than WHERE age < 18
>= Greater than or equal WHERE rating >= 4
<= Less than or equal WHERE price <= 100
LIKE Simple pattern matching WHERE name LIKE 'Dav'
IN Check whether a specified value matches any value in a list or subquery WHERE country IN ('USA', 'UK')
BETWEEN Check whether a specified value is within a range of values WHERE rating BETWEEN 3 AND 5

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