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9.17. Row and Array Comparisons

This section describes several specialized constructs for making multiple comparisons between groups of values. These forms are syntactically related to the subquery forms of the previous section, but do not involve subqueries. The forms involving array subexpressions are PostgreSQL extensions; the rest are SQL-compliant. All of the expression forms documented in this section return Boolean (true/false) results.

9.17.1. IN


expression
 IN (
value
[, ...])

The right-hand side is a parenthesized list of scalar expressions. The result is "true" if the left-hand expression's result is equal to any of the right-hand expressions. This is a shorthand notation for


expression
 = 
value1

OR

expression
 = 
value2

OR
...

Note that if the left-hand expression yields null, or if there are no equal right-hand values and at least one right-hand expression yields null, the result of the IN construct will be null, not false. This is in accordance with SQL's normal rules for Boolean combinations of null values.

9.17.2. NOT IN


expression
 NOT IN (
value
[, ...])

The right-hand side is a parenthesized list of scalar expressions. The result is "true" if the left-hand expression's result is unequal to all of the right-hand expressions. This is a shorthand notation for


expression
 <> 
value1

AND

expression
 <> 
value2

AND
...

Note that if the left-hand expression yields null, or if there are no equal right-hand values and at least one right-hand expression yields null, the result of the NOT IN construct will be null, not true as one might naively expect. This is in accordance with SQL's normal rules for Boolean combinations of null values.

Tip: x NOT IN y is equivalent to NOT (x IN y) in all cases. However, null values are much more likely to trip up the novice when working with NOT IN than when working with IN. It's best to express your condition positively if possible.

9.17.3. ANY/SOME (array)


expression
 
operator
 ANY (
array expression
)

expression
 
operator
 SOME (
array expression
)

The right-hand side is a parenthesized expression, which must yield an array value. The left-hand expression is evaluated and compared to each element of the array using the given operator , which must yield a Boolean result. The result of ANY is "true" if any true result is obtained. The result is "false" if no true result is found (including the special case where the array has zero elements).

SOME is a synonym for ANY.

9.17.4. ALL (array)


expression
 
operator
 ALL (
array expression
)

The right-hand side is a parenthesized expression, which must yield an array value. The left-hand expression is evaluated and compared to each element of the array using the given operator , which must yield a Boolean result. The result of ALL is "true" if all comparisons yield true (including the special case where the array has zero elements). The result is "false" if any false result is found.

9.17.5. Row-wise Comparison


row_constructor
 
operator
 
row_constructor

Each side is a row constructor, as described in Section 4.2.11. The two row values must have the same number of fields. Each side is evaluated and they are compared row-wise. Presently, only = and <> operators are allowed in row-wise comparisons. The result is "true" if the two rows are equal or unequal, respectively.

As usual, null values in the rows are combined per the normal rules of SQL Boolean expressions. Two rows are considered equal if all their corresponding members are non-null and equal; the rows are unequal if any corresponding members are non-null and unequal; otherwise the result of the row comparison is unknown (null).


row_constructor
 IS DISTINCT FROM 
row_constructor

This construct is similar to a <> row comparison, but it does not yield null for null inputs. Instead, any null value is considered unequal to (distinct from) any non-null value, and any two nulls are considered equal (not distinct). Thus the result will always be either true or false, never null.


row_constructor
 IS NULL

row_constructor
 IS NOT NULL

These constructs test a row value for null or not null. A row value is considered not null if it has at least one field that is not null.


 
 
  Published courtesy of The PostgreSQL Global Development Group Design by Interspire