The WHERE
clause is one of the fundamental building blocks of a SQL SELECT
statement. In this article we'll explain how it works.
The WHERE
clause is formed of the reserved 'where' keyword followed by what is known as a predicate expression - simply an expression which returns true
or false
.
If, for a given row, the predicate returns true
, that row will be included in the output of the query.
If the predicate returns false
, that row will be excluded.
Let's look at some examples.
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In this article the code snippets are written in the Google BigQuery Standard SQL syntax.
Simple WHERE
expressions
In these examples, the predicate expression in the WHERE
clause is a simple boolean expression - an expression that returns true
or false
.
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Inequality
IS NOT NULL
Compound WHERE
expressions
In the following examples, the WHERE
clause contains more complex predicate expressions, using the building blocks of the AND
and OR
logical operators.
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SELECT statements
WHERE
expressions on dates
When using dates and times, all of the same rules apply. The predicate expression in the WHERE
clause must still return true
or false
, but you are free to use functions and compound logical expressions.
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dates |
---|
2020-01-06 |
2020-01-07 |
2020-01-08 |
2020-01-09 |
2020-01-10 |
dates |
---|
2020-01-02 |
2020-01-03 |
2020-01-04 |
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