Progress
SQL-89
Guide and Reference


Logical Expressions

Logical expressions are expressions that evaluate to TRUE, FALSE, or UNKNOWN (equivalent to the Progress unknown value and to the Progress/SQL null value). You combine logical expressions with the logical operators AND and OR, and you negate a logical expression by prepending the logical operator NOT. The resulting logical expression has the value TRUE, FALSE, or UNKNOWN.

If you combine two logical expressions using AND, determine the truth value of the result from Table 2–2.

Table 2–2: Truth Table for AND  
AND
TRUE
UNKNOWN
FALSE
TRUE
TRUE
UNKNOWN
FALSE
UNKNOWN
UNKNOWN
UNKNOWN
FALSE
FALSE
FALSE
FALSE
FALSE

If you combine two logical expressions using OR, determine the truth value of the result from Table 2–3.

Table 2–3: Truth Table for OR  
OR
TRUE
UNKNOWN
FALSE
TRUE
TRUE
TRUE
TRUE
UNKNOWN
TRUE
UNKNOWN
UNKNOWN
FALSE
TRUE
UNKNOWN
FALSE

If you prepend NOT to a logical expression, determine the truth value of the result from Table 2–4.

Table 2–4: Truth Table for NOT  
NOT
 
TRUE
FALSE
UNKNOWN
UNKNOWN
FALSE
TRUE


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