# Boolean expression

Boolean expressions are allowed in WHERE clauses and in check constraints. Boolean expressions in check constraints have limitations not noted here; see CONSTRAINT clause for more information. Boolean expressions in a WHERE clause have a highly liberal syntax; see WHERE clause, for example.

A boolean expression can include a boolean operator or operators. These are listed in SQL Boolean Operators.

Table 1. SQL Boolean Operators
Operator | Explanation and Example | Syntax
--- | --- | ---
AND, OR, NOT | Evaluate any operand(s) that are boolean expressions
    (orig_airport = 'SFO') OR
        (dest_airport = 'GRU')
        -- returns true
    {
      Expression AND
        Expression |
      Expression OR
        Expression |
      NOT Expression
    }
Comparisons | <, =, >, <=, >=, <> are applicable to all of the built-in types.
    DATE('1998-02-26') <
        DATE('1998-03-01')
    -- returns true
    Expression
    {
      < |
      = |
      > |
      <= |
      >= |
      <>
    }
    Expression
IS NULL, IS NOT NULL | Test whether the result of an expression is null or not.
    WHERE MiddleName IS NULL
    Expression IS [ NOT ]
      NULL
LIKE | Attempts to match a character expression to a character pattern, which is a character string that includes one or more wildcards. % matches any number (zero or more) of characters in the corresponding position in first character expression. _ matches one character in the corresponding position in the character expression. Any other character matches only that character in the corresponding position in the character expression.
    city LIKE 'Sant_'
To treat % or _ as constant characters, escape the character with an optional escape character, which you specify with the ESCAPE clause.
    SELECT a FROM tabA WHERE a
    LIKE '%=_' ESCAPE '='
    CharacterExpression
      [ NOT ] LIKE
      CharacterExpression
      WithWildCard
      [ ESCAPE

    'escapeCharacter']
BETWEEN | Tests whether the first operand is between the second and third operands. The second operand must be less than the third operand. Applicable only to types to which <= and >= can be applied.
    WHERE booking_date BETWEEN
        DATE('1998-02-26') AND
        DATE('1998-03-01')
    Expression [ NOT ]
    BETWEEN Expression
      AND Expression
IN | Operates on table subquery or list of values. Returns TRUE if the left expression's value is in the result of the table subquery or in the list of values. Table subquery can return multiple rows but must return a single column.
    WHERE booking_date NOT IN
        (SELECT booking_date FROM
    HotelBookings WHERE rooms_available = 0)
    {
      Expression [ NOT ]
        IN
        TableSubquery |
      Expression [ NOT ]
        IN ( Expression
        [, Expression ]* )
    }
EXISTS | Operates on a table subquery. Returns TRUE if the table subquery returns any rows, and FALSE if it returns no rows. Table subquery can return multiple columns (only if you use * to denote multiple columns) and rows.
    WHERE EXISTS
      (SELECT *
      FROM Flights
      WHERE dest_airport = 'SFO'
      AND orig_airport = 'GRU')
    [NOT] EXISTS TableSubquery
Quantified comparison | A quantified comparison is a comparison operator (<, =, >, <=, >=, <>) with ALL or ANY or SOME applied. Operates on table subqueries, which can return multiple rows but must return a single column. If ALL is used, the comparison must be true for all values returned by the table subquery. If ANY or SOME is used, the comparison must be true for at least one value of the table subquery. ANY and SOME are equivalent.
    WHERE normal_rate < ALL
    (SELECT budget/550 FROM Groups)
    Expression
      ComparisonOperator
      {
        ALL |
        ANY |
        SOME
      }
      TableSubquery

Parent topic: SQL expressions
Related concepts
Dynamic parameters
Related reference
Expression precedence