Boolean expressions Boolean expressions are expressions that result in boolean values. Boolean expressionsBoolean operatorspart of WHERE clauseAND boolean operator OR boolean operatorNOT boolean operator Comparison boolean operatorsIS NULL boolean operatorIS NOT NULL boolean operatorLIKE boolean operatorLIKEescape character for BETWEEN boolean operatorIN boolean operator EXISTS boolean operatorQuantified comparison boolean operator

Most of the expressions listed in the table can result in boolean values.

Boolean expressions are allowed in the following clauses and operations:

  • WHERE clause
  • Check constraints (boolean expressions in check constraints have limitations; see for details)
  • CASE expression
  • HAVING clause (with restrictions)
  • ON clauses of INNER JOIN, LEFT OUTER JOIN, and RIGHT OUTER JOIN operations

A boolean expression can include a boolean operator or operators. These operators are listed in the following table.

SQL boolean operatorsThis table lists, describes, and provides the syntax for the 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 also accepts the != operator, which is not included in the SQL standard. 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 '='

When LIKE comparisons are used, compares one character at a time for non-metacharacters. This is different than the way processes = comparisons. The comparisons with the = operator compare the entire character string on left side of the = operator with the entire character string on the right side of the = operator. For more information, see "Character-based collation in " in the . 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. A table subquery can return 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