Search condition

A search condition is a condition used to select rows. Only those rows are selected which return the truth value true for the specified search condition. Search conditions can occur in a number of SQL statements which allow selection of rows in WHERE, HAVING or ON clauses. They can also occur in a check constraint (see "Integrity constraint") or in a case expression (see "CASE expression").

A search condition comprises predicates (logical expressions) which can be linked by the logical operators AND, OR or NOT.

A search condition is evaluated by first evaluating the predicates and then applying the logical operators to the results. The usual precedence rules apply for evaluation: NOT takes precedence over AND, which takes precedence over OR. Parentheses can be used to influence the evaluation sequence.

A search condition returns the truth value true, false or unknown.

AND Operand2 Operand1	true	false	unknown
true	true	false	unknown
false	false	false	false
unknown	unknown	false	unknown

Table 32: Truth values for AND operations

OR Operand2 Operand1	true	false	unknown
true	true	true	true
false	true	false	unknown
unknown	true	unknown	unknown

Table 33: Truth values for OR operations

NOT Operand1
true	false
false	true
unknown	unknown

Table 34: Truth values with NOT