SQL WHERE

Internal

• SQL SELECT
• SQL UPDATE
• SQL DELETE

TODO

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Overview

The WHERE clause is the mechanism for filtering out unwanted data from the result set. The WHERE clause can be used with SELECT, UPDATE and DELETE, but not with INSERT. The WHERE clause may contain an arbitrary number of filter conditions separated by AND, OR and NOT operators. The filter conditions may be optionally grouped together with parentheses.

[...] WHERE <filter_condition> AND|OR <filter_condition> ...

SELECT * FROM person WHERE person.name = 'Alice' AND (person.eye_color = 'blue' OR person.eye_color = 'black');

Using Parentheses

If the WHERE clause includes three or more conditions combined with AND, OR or NOT, you should use parentheses to make your intent clear.

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Filter Conditions

A condition is made up of one or more expressions, combined with one or more operators. An expression can be any of the following:

• A number
• A column in a table or a view
• A string literal
• A built-in function such as CONCAT()
• A subquery
• A list of expressions such as ('A', 'B', 'C')

The operators used within conditions include:

• Comparison operators: =, !=, <, >, <>, LIKE, IN, BETWEEN.
• Arithmetic operators: +, -, /, *

Equality Conditions

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Inequality Conditions

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Existence Conditions

EXISTS

Range Conditions

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The BETWEEN Operator

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String Ranges

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Membership Conditions

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Using Subqueries

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Matching Conditions

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Using Regular Expressions

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NULL in Conditions

To test whether a value is NULL use the IS operator, not =:

SELECT * FROM person where name IS NULL;

The following syntax is incorrect, and while will not generate a syntax or runtime error, it will produce invalid results, it will return no rows:

SELECT * FROM person where name = NULL;

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Also see:

NULL

SQL Conditional Logic

SQL Conditional Logic