SQL WHERE clause instance

The WHERE clause specifies the criteria for selection.

WHERE clause

To SELECT data from a table with conditions, you can add the WHERE clause to the SELECT statement.

Syntax

SELECT column name FROM table name WHERE column operator Value

The following operators can be used in the WHERE clause:

Operator	Description
=	Equal
<>	Not equal
>	Greater
<	Less
> =	Greater than or equal
<=	Less than or equal
BETWEEN	Within a certain range
LIKE	Search for a certain mode

Note: In some SQL versions, the operator <> can be written! =.

Use WHERE clause

If you only want to SELECT a person in the city "Beijing", you need to add the WHERE clause to the SELECT statement:

SELECT * FROM Persons WHERE City='Beijing'

"Persons" table

LastName	FirstName	Address	City	Year
Adams	John	Oxford Street	London	1970
Bush	George	Th Avenue	New York	1975
Carter	Thomas	Changan Street	Beijing	1980
Gates	Bill	Xuanwumen 10	Beijing	1985

Result:

LastName	FirstName	Address	City	Year
Carter	Thomas	Changan Street	Beijing	1980
Gates	Bill	Xuanwumen 10	Beijing	1985

Use of quotation marks

Note that we use single quotes around the condition values in the example.

Use single quotes to enclose SQL statementsText Value(Most database tutorial systems also accept double quotation marks ). If yesValueDo not use quotation marks.

Text value:

This is correct: SELECT * FROM Persons WHEREFirstName='Bush'This is incorrect: SELECT * FROM Persons WHEREFirstName=Bush

Value:

This is correct: SELECT * FROM Persons WHEREYear>1965This is incorrect: SELECT * FROM Persons WHEREYear>'1965'