GROUPING SETS

功能描述

GROUPING SETS生成交叉表格行，可以实现GROUP BY字段的交叉统计。

语法格式

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

关键字

GROUPING SETS：为对GROUP BY的扩展，例如

• SELECT a, b, sum(expression) FROM table GROUP BY a, b GROUPING SETS((a,b));
  将转换为以下一条查询：

  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);

  将转换为以下两条查询：

  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);
  将转换为以下两条查询：

  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, ());
  将转换为以下四条查询：

  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;

注意事项

• 所要分组的表必须是已经存在的表，否则会出错。
• 不同于ROLLUP，GROUPING SETS目前仅支持一种格式。

示例

根据group_id与job两个字段生成交叉表格行，返回每种聚合情况下的salary总和。

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