where

In SQL, the WHERE clause limits the processing of a query by defining the criteria each row must meet to be acceptable. It immediately follows the FROM clause. WHERE is one of the workhorse keywords in SQL because it is used so often in nearly every kind of query. SELECT statements use WHERE to limit the output. In UPDATE and DELETE statements, WHERE is used to limit the number of rows affected. To my knowledge, there is no reason to have a WHERE clause in an INSERT statement, nor do I believe any query engines allow it.

The WHERE clause causes the row to be returned as output or the statement to execute if the specified criteria, called the predicate, returns a true value. The predicate is merely a logical expression. The predicate can be as simple as specifying a constant value a particular column must have, or it can consist of a complicated subquery or correlated subquery.

As a logical expression, the predicate can use any of the logical operators (AND, OR, NOT, etc.) to create compound expressions. There is no limit to the number of expressions in the predicate or complexity except for the processing power of the computer on which the query runs. The predicate also makes use of the relational operators to compare one term of the expression to the other.

The simplest WHERE clauses takes the form

  ... WHERE column_name = "value" ...

   ... WHERE (column1 > "value1") AND 
              (column2 < "value2") ... 

Wher (?), Where (), pron. & conj. [See Whether.]

Whether.

Piers Plowman.

Men must enquire (this is mine assent), Wher she be wise or sober or dronkelewe. Chaucer.

© Webster 1913.

Where (?), adv. [OE. wher, whar, AS. hwr; akin to D. waar, OS. hwr, OHG. hwar, war, wa, G. wo, Icel. and Sw. hvar, Dan. hvor, Goth. hwar, and E. who; cf. Skr. karhi when. See Who, and cf. There.]

1.

At or in what place; hence, in what situation, position, or circumstances; -- used interrogatively.

God called unto Adam, . . . Where art thou? Gen. iii. 9.

See the Note under What, pron., 1.

2.

At or in which place; at the place in which; hence, in the case or instance in which; -- used relatively.

She visited that place where first she was so happy. Sir P. Sidney.

Where I thought the remnant of mine age Should have been cherished by her childlike duty. Shak.

Where one on his side fights, thousands will fly. Shak.

But where he rode one mile, the dwarf ran four. Sir W. Scott.

3.

To what or which place; hence, to what goal, result, or issue; whither; -- used interrogatively and relatively; as, where are you going?

But where does this tend? Goldsmith.

Lodged in sunny cleft, Where the gold breezes come not. Bryant.

Where is often used pronominally with or without a preposition, in elliptical sentences for a place in which, the place in which, or what place.

The star . . . stood over where the young child was. Matt. ii. 9.

The Son of man hath not where to lay his head. Matt. viii. 20.

Within about twenty paces of where we were. Goldsmith.

Where did the minstrels come from? Dickens.

⇒ Where is much used in composition with preposition, and then is equivalent to a pronoun. Cf. Whereat, Whereby, Wherefore, Wherein, etc.

Where away Naut., in what direction; as, where away is the land?

Syn. -- See Whither.

© Webster 1913.

Where, conj.

Whereas.

And flight and die is death destroying death; Where fearing dying pays death servile breath. Shak.

© Webster 1913.

Where, n.

Place; situation.

Finding the nymph asleep in secret where. Spenser.

© Webster 1913.