Each IF command
evaluates every case in the data. Compare IF with DO IF, which
passes control for a case out of the DO IF—END
IF structure as soon as a logical condition is met.
The logical expression is evaluated as true, false,
or missing. The assignment is executed only if the logical expression
is true. If the logical expression is false or missing, the assignment
is not made. Existing target variables remain unchanged; new numeric
variables retain their initial (system-missing) values.
In general, a logical expression is evaluated as
missing if any one of the variables used in the logical expression
is system- or user-missing. However, when relations are joined by
the logical operators AND or OR, the expression can sometimes be evaluated
as true or false even when variables have missing values. See the topic Missing Values and Logical Operators (IF command) for more information.