Logical expressions

Logical expressions return the boolean value true if both of two expressions are true, or if one or both of two expressions are true. The operators that are used in logical expressions include and and or.

The following table describes these operators, listed in order of operator precedence from highest to lowest.

Table 1. Logical expression operators in XQuery
Operator	Purpose
and	Returns true if both expressions are true.
or	Returns true if one or both expressions are true.

Restriction: The operand of a logical expression cannot contain an FLWOR expression.

The result of a logical expression is a boolean value or an error. XQuery uses the following process to evaluate a logical expression.

Determines the effective boolean value (EBV) of each operand.
Applies the operator to the effective boolean values of the operands. The result is a boolean value or an error. Table 2 shows the results that are returned by a logical expression based on the EBV of its operands and any errors that are encountered during the evaluation of an operand.

Table 2. Results of logical expressions based on effective boolean values (EBVs) of operands
EBV of operand 1	Operator	EBV of operand 2	Result
true	and	true	true
true	and	false	false
false	and	true	false
false	and	false	false
true	and	error	error
error	and	true	error
false	and	error	false or error
error	and	false	false or error
error	and	error	error
true	or	true	true
false	or	false	false
true	or	false	true
false	or	true	true
true	or	error	true or error
error	or	true	true or error
false	or	error	error
error	or	false	error
error	or	error	error

Syntax

logical expression

Examples

The following query uses a logical expression to retrieve records from a table for 22-inch snow shovels or 24-inch snow shovels.

SELECT XMLQUERY ('declare namespace pos="http://posample.org";
  /pos:product/description[name = "Snow Shovel, Deluxe 24"""
  or name = "Snow Shovel, Basic 22"""]'
  PASSING DESCRIPTION) 
FROM T1;