sql_cond - AND, OR, NOT, ( )
... sql_cond1 AND sql_cond2 AND sql_cond3 ...
... sql_cond1 OR sql_cond2 OR sql_cond3 ...
... NOT sql_cond ...
... ( sql_cond ) ...
Any number of logical
expressions can be joined to make one logical expression using
OR and the result of a logical expression can be negated using
NOT. The same
rules apply as to general logical expressions, with
the difference that the operator
NOT cannot be specified more than once consecutively. In particular, the explicit use of
( ) parentheses is also possible.
The following additional rules apply to logical expressions whose result is unknown (because an operand has the null value):
ANDjoin of two unknown expressions or one true expression with an unknown expression produces an unknown expression. An
ANDjoin of a false expression with an unknown expression produces a false expression.
ORjoin of two unknown expressions or one false expression with an unknown expression produces an unknown expression. An
ORjoin of one true and one unknown expression produces a true expression.
- The negation of an unknown expression with
NOTproduces an unknown expression.
- In particular, the expressions specified dynamically
(cond_syntax)are also possible as logical expressions within a join or negation.
- The operator
WHEREclause cannot be supported by an index. For this reason, it is best to use the reverse relational operator instead of
NOT, for example
col <= dobjinstead of
NOT col > dobj.
NOToperators can only be specified consecutively if they are separated by an opening parenthesis. If not, an even number of consecutive
NOTs has the same meaning as none and an odd number of consecutive
NOTs has the same meaning as a single
NOTand should be used accordingly.
Reads flights from Frankfurt to Los Angeles or San Francisco.
SELECT * FROM spfli WHERE cityfrom = 'FRANKFURT' AND ( cityto = 'LOS ANGELES' OR cityto = 'SAN FRANCISCO' ) INTO TABLE @DATA(spfli_tab).