GROUPING SETS

Function

This statement is used to generate the cross-table row and achieve the cross-statistics of the GROUP BY field.

Syntax

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SELECT attr_expr_list FROM table_reference
  GROUP BY col_name_list
  GROUPING SETS(col_name_list);

Keyword

GROUPING SETS is the expansion of GROUP BY. For example:

• SELECT a, b, sum(expression) FROM table GROUP BY a, b GROUPING SETS((a,b));
  It can be converted to the following query:

  1 2	SELECT a, b, sum(expression) FROM table GROUP BY a, b;

• SELECT a, b, sum(expression) FROM table GROUP BY a, b GROUPING SETS(a,b);

  It can be converted to the following two queries:

  1 2 3

  SELECT a, NULL, sum(expression) FROM table GROUP BY a; UNION SELECT NULL, b, sum(expression) FROM table GROUP BY b;

• SELECT a, b, sum(expression) FROM table GROUP BY a, b GROUPING SETS((a,b), a);
  It can be converted to the following two queries:

  1 2 3

  SELECT a, b, sum(expression) FROM table GROUP BY a, b; UNION SELECT a, NULL, sum(expression) FROM table GROUP BY a;

• SELECT a, b, sum(expression) FROM table GROUP BY a, b GROUPING SETS((a,b), a, b, ());
  It can be converted to the following four queries:

  1 2 3 4 5 6 7

  SELECT a, b, sum(expression) FROM table GROUP BY a, b; UNION SELECT a, NULL, sum(expression) FROM table GROUP BY a, NULL; UNION SELECT NULL, b, sum(expression) FROM table GROUP BY NULL, b; UNION SELECT NULL, NULL, sum(expression) FROM table;

Precautions

• The to-be-grouped table must exist. Otherwise, an error is reported.
• Different from ROLLUP, there is only one syntax for GROUPING SETS.

Example

To generate the cross-table row according to the group_id and job fields and return the total salary on each aggregation condition, run the following statement:

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SELECT group_id, job, SUM(salary) FROM group_test
  GROUP BY group_id, job
  GROUPING SETS (group_id, job);