GROUP BY 子句

项目
07/05/2024

适用于： 勾选“是” Databricks SQL Databricks Runtime

使用 GROUP BY 子句基于一组指定的分组表达式对行进行分组，并基于一个或多个指定的聚合函数对行组计算聚合。 Databricks SQL 还支持高级聚合，以通过 GROUPING SETS、CUBE 和 ROLLUP 子句对同一输入记录集执行多次聚合。分组表达式和高级聚合可以在 GROUP BY 子句中混合使用，并在 GROUPING SETS 子句中嵌套使用。

请参阅混合/嵌套分组分析部分中的详细信息。

将 FILTER 子句附加到聚合函数时，只会将匹配的行传递给该函数。

语法

GROUP BY ALL

GROUP BY group_expression [, ...] [ WITH ROLLUP | WITH CUBE ]

GROUP BY { group_expression | { ROLLUP | CUBE | GROUPING SETS } ( grouping_set [, ...] ) } [, ...]

grouping_set
   { expression |
     ( [ expression [, ...] ] ) }

而聚合函数被定义为

aggregate_name ( [ DISTINCT ] expression [, ...] ) [ FILTER ( WHERE boolean_expression ) ]

参数

ALL

适用于： Databricks SQL Databricks Runtime 12.2 LTS 及更高版本

一种简写表示法，用于将所有不包含聚合函数的 SELECT 列表表达式作为 group_expression 添加。如果不存在此类表达式，则 GROUP BY ALL 等同于省略导致全局聚合的 GROUP BY 子句。

GROUP BY ALL 不保证生成一组可以解析的组表达式。如果生成的子句格式不正确，Azure Databricks 将引发 UNRESOLVED_ALL_IN_GROUP_BY 或 MISSING_AGGREGATION。
group_expression

指定将行分组到一起的条件。基于分组表达式的结果值执行行的分组。分组表达式可以是列别名称（如 GROUP BY a）、列位置（如 GROUP BY 0）或表达式（如 GROUP BY a + b）。如果 group_expression 包含聚合函数，则 Azure Databricks 会引发 GROUP_BY_AGGREGATE 错误。
grouping_set

分组集由括号中的零个或多个逗号分隔的表达式指定。如果分组集只有一个元素，则可以省略括号。例如，GROUPING SETS ((a), (b)) 和 GROUPING SETS (a, b) 相同。
GROUPING SETS

对 GROUPING SETS 之后指定的每个分组集的行进行分组。例如：

GROUP BY GROUPING SETS ((warehouse), (product)) 在语义上等效于 GROUP BY warehouse 和 GROUP BY product 的结果的并集。

该子句是 UNION ALL 的简写形式，其中 UNION ALL 运算符的每个段执行 GROUPING SETS 子句中指定的每个分组集的聚合。

同样，GROUP BY GROUPING SETS ((warehouse, product), (product), ()) 在语义上等效于 GROUP BY warehouse, product、GROUP BY product 和全局聚合的结果的并集。

注意

对 Hive 兼容 Databricks SQL，允许 GROUP BY ... GROUPING SETS (...)。通常会忽略 GROUP BY 表达式，但如果它们包含 GROUPING SETS 表达式以外的其他表达式，则额外的表达式将包含在分组表达式中，并且值始终为 null。例如，SELECT a, b, c FROM ... GROUP BY a, b, c GROUPING SETS (a, b)，列 c 的输出始终为 null。

ROLLUP

在一个语句中指定多个级别的聚合。此子句用于基于多个分组集计算聚合。 ROLLUP 是 GROUPING SETS 的速记。例如：

GROUP BY warehouse, product WITH ROLLUP 或 GROUP BY ROLLUP(warehouse, product) 相当于

GROUP BY GROUPING SETS((warehouse, product), (warehouse), ())。

当 GROUP BY ROLLUP(warehouse, product, (warehouse, location))

相当于 GROUP BY GROUPING SETS((warehouse, product, location), (warehouse, product), (warehouse), ())。

ROLLUP 规范的 N 个元素将得到 N+1 个 GROUPING SETS。
CUBE

CUBE 子句用于根据 GROUP BY 子句中指定的分组列的组合执行聚合。 CUBE 是 GROUPING SETS 的速记。例如：

GROUP BY warehouse, product WITH CUBE 或 GROUP BY CUBE(warehouse, product) 相当于

GROUP BY GROUPING SETS((warehouse, product), (warehouse), (product), ())。

GROUP BY CUBE(warehouse, product, (warehouse, location)) 等效于以下查询：
```
GROUP BY GROUPING SETS((warehouse, product, location), (warehouse, product), (warehouse, location), (product, warehouse, location), (warehouse), (product), (warehouse, product), ())
```
CUBE 规范的 N 个元素将得到 2^N 个 GROUPING SETS。
aggregate_name

聚合函数名称（MIN、MAX、COUNT、SUM、AVG 等）。
DISTINCT

在将输入行传递给聚合函数之前，将其中的重复项删除。
FILTER

筛选 WHERE 子句中 boolean_expression 计算结果为 true 的输入行，并将其传递给聚合函数；将放弃其他行。

混合/嵌套的分组分析

GROUP BY 子句可以包括多个 group_expressions 和多个 CUBE、ROLLUP 和 GROUPING SETS。

GROUPING SETS 还可以具有嵌套 CUBE、ROLLUP 或 GROUPING SETS 的子句。例如：

GROUPING SETS(ROLLUP(warehouse, location), CUBE(warehouse, location)), GROUPING SETS(warehouse, GROUPING SETS(location, GROUPING SETS(ROLLUP(warehouse, location), CUBE(warehouse, location))))

CUBE 和 ROLLUP 只是 GROUPING SETS 的语法。请参阅上述部分，了解如何将 CUBE 和 ROLLUP 转换为 GROUPING SETS。 group_expression 可以在此上下文中视为单个组的 GROUPING SETS。

对于 GROUP BY 子句中的多个 GROUPING SETS，Databricks SQL 通过执行原始的 GROUPING SETS 的叉积生成单个 GROUPING SETS。

对于嵌套在 GROUPING SETS 子句中的 GROUPING SETS，Databricks SQL 采用其分组集并将其条带化。例如，以下查询：

GROUP BY warehouse, GROUPING SETS((product), ()), GROUPING SETS((location, size), (location), (size), ());

GROUP BY warehouse, ROLLUP(product), CUBE(location, size);

等效于以下查询：

GROUP BY GROUPING SETS( (warehouse, product, location, size), (warehouse, product, location), (warehouse, product, size), (warehouse, product), (warehouse, location, size), (warehouse, location), (warehouse, size), (warehouse))

当 GROUP BY GROUPING SETS(GROUPING SETS(warehouse), GROUPING SETS((warehouse, product)))

相当于 GROUP BY GROUPING SETS((warehouse), (warehouse, product))。

示例

CREATE TEMP VIEW dealer (id, city, car_model, quantity) AS
VALUES (100, 'Fremont', 'Honda Civic', 10),
       (100, 'Fremont', 'Honda Accord', 15),
       (100, 'Fremont', 'Honda CRV', 7),
       (200, 'Dublin', 'Honda Civic', 20),
       (200, 'Dublin', 'Honda Accord', 10),
       (200, 'Dublin', 'Honda CRV', 3),
       (300, 'San Jose', 'Honda Civic', 5),
       (300, 'San Jose', 'Honda Accord', 8);

-- Sum of quantity per dealership. Group by `id`.
> SELECT id, sum(quantity) FROM dealer GROUP BY id ORDER BY id;
  id sum(quantity)
 --- -------------
 100            32
 200            33
 300            13

-- Use column position in GROUP by clause.
> SELECT id, sum(quantity) FROM dealer GROUP BY 1 ORDER BY 1;
  id sum(quantity)
 --- -------------
 100            32
 200            33
 300            13

-- Multiple aggregations.
-- 1. Sum of quantity per dealership.
-- 2. Max quantity per dealership.
> SELECT id, sum(quantity) AS sum, max(quantity) AS max
    FROM dealer GROUP BY id ORDER BY id;
  id sum max
 --- --- ---
 100  32  15
 200  33  20
 300  13   8

-- Count the number of distinct dealers in cities per car_model.
> SELECT car_model, count(DISTINCT city) AS count FROM dealer GROUP BY car_model;
    car_model count
 ------------ -----
  Honda Civic     3
    Honda CRV     2
 Honda Accord     3

-- Count the number of distinct dealers in cities per car_model, using GROUP BY ALL
> SELECT car_model, count(DISTINCT city) AS count FROM dealer GROUP BY ALL;
    car_model count
 ------------ -----
  Honda Civic     3
    Honda CRV     2
 Honda Accord     3

-- Sum of only 'Honda Civic' and 'Honda CRV' quantities per dealership.
> SELECT id,
         sum(quantity) FILTER (WHERE car_model IN ('Honda Civic', 'Honda CRV')) AS `sum(quantity)`
    FROM dealer
    GROUP BY id ORDER BY id;
  id sum(quantity)
 --- -------------
 100            17
 200            23
 300             5

-- Aggregations using multiple sets of grouping columns in a single statement.
-- Following performs aggregations based on four sets of grouping columns.
-- 1. city, car_model
-- 2. city
-- 3. car_model
-- 4. Empty grouping set. Returns quantities for all city and car models.
> SELECT city, car_model, sum(quantity) AS sum
    FROM dealer
    GROUP BY GROUPING SETS ((city, car_model), (city), (car_model), ())
    ORDER BY city;
      city    car_model sum
 --------- ------------ ---
      null         null  78
      null  HondaAccord  33
      null     HondaCRV  10
      null   HondaCivic  35
    Dublin         null  33
    Dublin  HondaAccord  10
    Dublin     HondaCRV   3
    Dublin   HondaCivic  20
   Fremont         null  32
   Fremont  HondaAccord  15
   Fremont     HondaCRV   7
   Fremont   HondaCivic  10
  San Jose         null  13
  San Jose  HondaAccord   8
  San Jose   HondaCivic   5

-- Group by processing with `ROLLUP` clause.
-- Equivalent GROUP BY GROUPING SETS ((city, car_model), (city), ())
> SELECT city, car_model, sum(quantity) AS sum
    FROM dealer
    GROUP BY city, car_model WITH ROLLUP
    ORDER BY city, car_model;
      city    car_model sum
 --------- ------------ ---
      null         null  78
    Dublin         null  33
    Dublin  HondaAccord  10
    Dublin     HondaCRV   3
    Dublin   HondaCivic  20
   Fremont         null  32
   Fremont  HondaAccord  15
   Fremont     HondaCRV   7
   Fremont   HondaCivic  10
  San Jose         null  13
  San Jose  HondaAccord   8
  San Jose   HondaCivic   5

-- Group by processing with `CUBE` clause.
-- Equivalent GROUP BY GROUPING SETS ((city, car_model), (city), (car_model), ())
> SELECT city, car_model, sum(quantity) AS sum
    FROM dealer
    GROUP BY city, car_model WITH CUBE
    ORDER BY city, car_model;
      city    car_model sum
 --------- ------------ ---
      null         null  78
      null  HondaAccord  33
      null     HondaCRV  10
      null   HondaCivic  35
    Dublin         null  33
    Dublin  HondaAccord  10
    Dublin     HondaCRV   3
    Dublin   HondaCivic  20
   Fremont         null  32
   Fremont  HondaAccord  15
   Fremont     HondaCRV   7
   Fremont   HondaCivic  10
  San Jose         null  13
  San Jose  HondaAccord   8
  San Jose   HondaCivic   5

--Prepare data for ignore nulls example
> CREATE TEMP VIEW person (id, name, age) AS
   VALUES (100, 'Mary', NULL),
          (200, 'John', 30),
          (300, 'Mike', 80),
          (400, 'Dan' , 50);

--Select the first row in column age
> SELECT FIRST(age) FROM person;
  first(age, false)
 --------------------
  NULL

--Get the first row in column `age` ignore nulls,last row in column `id` and sum of column `id`.
> SELECT FIRST(age IGNORE NULLS), LAST(id), SUM(id) FROM person;
  first(age, true)    last(id, false)    sum(id)
 ------------------- ------------------ ----------
  30                  400                1000

通过

GROUP BY 子句

语法

参数

混合/嵌套的分组分析

示例

相关文章

其他资源