SQL WHERE Clause instance

The WHERE clause is used to specify criteria for selection.

WHERE clause

If you want to conditionally select data from a table, you can add a WHERE clause to the SELECT statement.

Grammar

SELECT column name from table name WHERE column operator value

The following operators can be used in the WHERE clause:

operator	Description
=	Equals
<>	Not equal to
>	Greater than
<	Less than
>=	Greater than or equal to
<=	Less than or equal to
BETWEEN	Within a certain range
Like	Search for a pattern

Note: in some versions of SQL, operator <> can be written as!=.

Use the WHERE clause

If you only want to select people who live in the city "Beijing," we need to add a WHERE clause to the SELECT statement:

WHERE City='Beijing'

"Persons" table

Address City Year

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

Results:

Address City Year

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

Use of Quotes

Notice that we use single quotes around the conditional values in the example.

SQL uses single quotes to surround text values (most database tutorial systems also accept double quotes). If this is a numeric value , do not use quotes.

Text value:

This is true:
FirstName='Bush'
This is wrong:
FirstName=Bush

Numerical:

This is true:
Year>1965
This is wrong:
Year>'1965'