![]() ![]() ![]() ![]() The fourth form invokes the aggregate once for each input row since no particular input value is specified, it is generally only useful for the count(*) aggregate function. The third form invokes the aggregate once for each distinct value of the expression (or distinct set of values, for multiple expressions) found in the input rows. The second form is the same as the first, since ALL is the default. The first form of aggregate expression invokes the aggregate once for each input row. The optional order_by_clause and filter_clause are described below. Where aggregate_name is a previously defined aggregate (possibly qualified with a schema name) and expression is any value expression that does not itself contain an aggregate expression or a window function call. The syntax of an aggregate expression is one of the following: aggregate_name ( expression ) Īggregate_name (ALL expression ) Īggregate_name (DISTINCT expression ) Īggregate_name ( * ) Īggregate_name ( ] ) WITHIN GROUP ( order_by_clause ) An aggregate function reduces multiple inputs to a single output value, such as the sum or average of the inputs. This notation behaves differently depending on context see Section 8.16.5 for details.Īn aggregate expression represents the application of an aggregate function across the rows selected by a query. You can ask for all fields of a composite value by writing. The parentheses are required here to show that compositecol is a column name not a table name, or that mytable is a table name not a schema name in the second case. (Thus, a qualified column reference is actually just a special case of the field selection syntax.) An important special case is extracting a field from a table column that is of a composite type: In general the row expression must be parenthesized, but the parentheses can be omitted when the expression to be selected from is just a table reference or positional parameter. If an expression yields a value of a composite type (row type), then a specific field of the row can be extracted by writing expression. ![]()
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