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Logical Operators

  • reference

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Logical terms let you combine other expressions using Boolean logic. SQL++ provides the following logical operators:

  • AND

  • OR

  • NOT

In SQL++, logical operators have their usual meaning; however, Boolean propositions can evaluate to NULL or MISSING as well as to TRUE and FALSE. The truth tables for these operators therefore use four-valued logic.

AND

and ::= cond 'AND' cond
Syntax diagram

AND evaluates to TRUE only if both conditions are TRUE.

Table 1. AND Truth Table
TRUE FALSE NULL MISSING

TRUE

TRUE

FALSE

NULL

MISSING

FALSE

FALSE

FALSE

FALSE

FALSE

NULL

NULL

FALSE

NULL

MISSING

MISSING

MISSING

FALSE

MISSING

MISSING

OR

or ::= cond 'OR' cond
Syntax diagram

OR evaluates to TRUE if one of the conditions is TRUE.

Table 2. OR Truth Table
TRUE FALSE NULL MISSING

TRUE

TRUE

TRUE

TRUE

TRUE

FALSE

TRUE

FALSE

NULL

MISSING

NULL

TRUE

NULL

NULL

NULL

MISSING

TRUE

MISSING

NULL

MISSING

NOT

not ::= 'NOT' cond
Syntax diagram

NOT evaluates to TRUE if the condition is FALSE, and vice versa.

Table 3. NOT Truth Table
NOT

TRUE

FALSE

FALSE

TRUE

NULL

NULL

MISSING

MISSING

For further details, refer to Boolean Logic.