# GROUP BY
# description
GROUP BY GROUPING SETS ｜ CUBE ｜ ROLLUP 是对 GROUP BY 子句的扩展，它能够在一个 GROUP BY 子句中实现多个集合的分组的聚合。其结果等价于将多个相应 GROUP BY 子句进行 UNION 操作。
GROUP BY 子句是只含有一个元素的 GROUP BY GROUPING SETS 的特例。 例如，GROUPING SETS 语句：
SELECT a, b, SUM( c ) FROM tab1 GROUP BY GROUPING SETS ( (a, b), (a), (b), ( ) );
其查询结果等价于：
SELECT a, b, SUM( c ) FROM tab1 GROUP BY a, b
UNION
SELECT a, null, SUM( c ) FROM tab1 GROUP BY a
UNION
SELECT null, b, SUM( c ) FROM tab1 GROUP BY b
UNION
SELECT null, null, SUM( c ) FROM tab1
GROUPING(expr) 指示一个列是否为聚合列，如果是聚合列为0，否则为1
GROUPING_ID(expr [ , expr [ , ... ] ]) 与GROUPING 类似， GROUPING_ID根据指定的column 顺序，计算出一个列列表的 bitmap 值，每一位为GROUPING的值. GROUPING_ID()函数返回位向量的十进制值。
# Syntax
SELECT ...
FROM ...
[ ... ]
GROUP BY [
, ... |
GROUPING SETS [, ...] ( groupSet [ , groupSet [ , ... ] ] ) |
ROLLUP(expr [ , expr [ , ... ] ]) |
expr [ , expr [ , ... ] ] WITH ROLLUP |
CUBE(expr [ , expr [ , ... ] ]) |
expr [ , expr [ , ... ] ] WITH CUBE
]
[ ... ]
# Parameters
groupSet 表示 select list 中的列，别名或者表达式组成的集合 groupSet ::= { ( expr [ , expr [ , ... ] ] )}
expr 表示 select list 中的列，别名或者表达式
# Note
doris 支持类似PostgreSQL 语法, 语法实例如下
SELECT a, b, SUM( c ) FROM tab1 GROUP BY GROUPING SETS ( (a, b), (a), (b), ( ) );
SELECT a, b,c, SUM( d ) FROM tab1 GROUP BY ROLLUP(a,b,c)
SELECT a, b,c, SUM( d ) FROM tab1 GROUP BY CUBE(a,b,c)
ROLLUP(a,b,c) 等价于如下GROUPING SETS 语句
GROUPING SETS (
(a,b,c),
( a, b ),
( a),
( )
)
CUBE ( a, b, c ) 等价于如下GROUPING SETS 语句
GROUPING SETS (
( a, b, c ),
( a, b ),
( a, c ),
( a ),
( b, c ),
( b ),
( c ),
( )
)
# example
下面是一个实际数据的例子
> SELECT * FROM t;
+------+------+------+
| k1 | k2 | k3 |
+------+------+------+
| a | A | 1 |
| a | A | 2 |
| a | B | 1 |
| a | B | 3 |
| b | A | 1 |
| b | A | 4 |
| b | B | 1 |
| b | B | 5 |
+------+------+------+
8 rows in set (0.01 sec)
> SELECT k1, k2, SUM(k3) FROM t GROUP BY GROUPING SETS ( (k1, k2), (k2), (k1), ( ) );
+------+------+-----------+
| k1 | k2 | sum(`k3`) |
+------+------+-----------+
| b | B | 6 |
| a | B | 4 |
| a | A | 3 |
| b | A | 5 |
| NULL | B | 10 |
| NULL | A | 8 |
| a | NULL | 7 |
| b | NULL | 11 |
| NULL | NULL | 18 |
+------+------+-----------+
9 rows in set (0.06 sec)
> SELECT k1, k2, GROUPING_ID(k1,k2), SUM(k3) FROM t GROUP BY GROUPING SETS ((k1, k2), (k1), (k2), ());
+------+------+---------------+----------------+
| k1 | k2 | grouping_id(k1,k2) | sum(`k3`) |
+------+------+---------------+----------------+
| a | A | 0 | 3 |
| a | B | 0 | 4 |
| a | NULL | 1 | 7 |
| b | A | 0 | 5 |
| b | B | 0 | 6 |
| b | NULL | 1 | 11 |
| NULL | A | 2 | 8 |
| NULL | B | 2 | 10 |
| NULL | NULL | 3 | 18 |
+------+------+---------------+----------------+
9 rows in set (0.02 sec)
# keyword
GROUP, GROUPING, GROUPING_ID, GROUPING_SETS, GROUPING SETS, CUBE, ROLLUP
