Three SQL WHERE clause (where)

Three SQL WHERE clause

WHERE clauses are used to specify criteria for selection

WHERE clause

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
= /td>	equals
<>	Not equal to
>	greater than
<	Less than
>=	greater than or equal to
<=	less than equals
between	Within a range
like	Search for a pattern

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

Using the WHERE clause

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

WHERE City=‘Beijing‘

"Persons" table

LastName	FirstName	Address	City	Year
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:

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.

SQL uses single quotation marks to wrap text values (most database systems also accept double quotes). If it is a numeric value , do not use quotation marks.

Text value:

That's right:

FirstName=‘Bush‘

This is wrong:

FirstName=Bush

Numerical:

That's right:

Year>1965

This is wrong:

Year>‘1965‘

Three SQL WHERE clause (where)