Logical expressions

Logical expressions use the operators and and or to compute a Boolean value (true or false).

The following table describes these operators and lists them 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.

The result of a logical expression is either a Boolean value (true or false) or an error. When a logical expression is evaluated, the effective Boolean value (EBV) of each operand is determined. The operator is then applied to the EBVs of the operands, and the result is either a boolean value or an error. If the EBV of an operand is an error, then the logical expression might result in an error. The following table shows the results that are returned by a logical expression based on the EBVs of its operands.

Table 2. Results of logical expressions based on 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

Tip: In addition to logical expressions, XQuery provides a function named fn:not that takes a general sequence as a parameter and returns a Boolean value.

Examples

The following expressions return true:
```
1 eq 1 and 2 eq 2
1 eq 1 or 2 eq 3
```
The following expression might return either false or an error:
```
1 eq 2 and 3 idiv 0 = 1
```
The following expression might return either true or an error:
```
1 eq 1 or 3 idiv 0 = 1
```
The following expression returns an error:
```
1 eq 1 and 3 idiv 0 = 1
```