SORT BY 子句
描述
SORT BY 子句用于在用户指定的顺序下，对每个分区内的结果行进行排序并返回。当存在多个分区时，SORT BY 可能会返回部分有序的结果。这与保证输出完全有序的 ORDER BY 子句不同。
语法
SORT BY { expression [ sort_direction | nulls_sort_order ] [ , ... ] }
参数
-
SORT BY
指定一个逗号分隔的表达式列表，以及可选参数
sort_direction和nulls_sort_order，这些参数用于对每个分区内的行进行排序。 -
sort_direction
可选地指定是按升序还是降序对行进行排序。排序方向的有效值为
ASC（升序）和DESC（降序）。如果未明确指定排序方向，则默认按升序排序。语法：
[ ASC | DESC ] -
nulls_sort_order
可选地指定 NULL 值是在非 NULL 值之前还是之后返回。如果未指定
null_sort_order，则在排序顺序为ASC时 NULL 值排在前面，在排序顺序为DESC时 NULL 值排在后面。- 如果指定了
NULLS FIRST，则无论排序顺序如何，NULL 值都会首先返回。 - 如果指定了
NULLS LAST，则无论排序顺序如何，NULL 值都会最后返回。
语法：
[ NULLS { FIRST | LAST } ] - 如果指定了
示例
CREATE TABLE person (zip_code INT, name STRING, age INT);
INSERT INTO person VALUES
(94588, 'Zen Hui', 50),
(94588, 'Dan Li', 18),
(94588, 'Anil K', 27),
(94588, 'John V', NULL),
(94511, 'David K', 42),
(94511, 'Aryan B.', 18),
(94511, 'Lalit B.', NULL);
-- Use `REPARTITION` hint to partition the data by `zip_code` to
-- examine the `SORT BY` behavior. This is used in rest of the
-- examples.
-- Sort rows by `name` within each partition in ascending manner
SELECT /*+ REPARTITION(zip_code) */ name, age, zip_code FROM person SORT BY name;
+--------+----+--------+
| name| age|zip_code|
+--------+----+--------+
| Anil K| 27| 94588|
| Dan Li| 18| 94588|
| John V|null| 94588|
| Zen Hui| 50| 94588|
|Aryan B.| 18| 94511|
| David K| 42| 94511|
|Lalit B.|null| 94511|
+--------+----+--------+
-- Sort rows within each partition using column position.
SELECT /*+ REPARTITION(zip_code) */ name, age, zip_code FROM person SORT BY 1;
+--------+----+--------+
| name| age|zip_code|
+--------+----+--------+
| Anil K| 27| 94588|
| Dan Li| 18| 94588|
| John V|null| 94588|
| Zen Hui| 50| 94588|
|Aryan B.| 18| 94511|
| David K| 42| 94511|
|Lalit B.|null| 94511|
+--------+----+--------+
-- Sort rows within partition in ascending manner keeping null values to be last.
SELECT /*+ REPARTITION(zip_code) */ age, name, zip_code FROM person SORT BY age NULLS LAST;
+----+--------+--------+
| age| name|zip_code|
+----+--------+--------+
| 18| Dan Li| 94588|
| 27| Anil K| 94588|
| 50| Zen Hui| 94588|
|null| John V| 94588|
| 18|Aryan B.| 94511|
| 42| David K| 94511|
|null|Lalit B.| 94511|
+----+--------+--------+
-- Sort rows by age within each partition in descending manner, which defaults to NULL LAST.
SELECT /*+ REPARTITION(zip_code) */ age, name, zip_code FROM person SORT BY age DESC;
+----+--------+--------+
| age| name|zip_code|
+----+--------+--------+
| 50| Zen Hui| 94588|
| 27| Anil K| 94588|
| 18| Dan Li| 94588|
|null| John V| 94588|
| 42| David K| 94511|
| 18|Aryan B.| 94511|
|null|Lalit B.| 94511|
+----+--------+--------+
-- Sort rows by age within each partition in descending manner keeping null values to be first.
SELECT /*+ REPARTITION(zip_code) */ age, name, zip_code FROM person SORT BY age DESC NULLS FIRST;
+----+--------+--------+
| age| name|zip_code|
+----+--------+--------+
|null| John V| 94588|
| 50| Zen Hui| 94588|
| 27| Anil K| 94588|
| 18| Dan Li| 94588|
|null|Lalit B.| 94511|
| 42| David K| 94511|
| 18|Aryan B.| 94511|
+----+--------+--------+
-- Sort rows within each partition based on more than one column with each column having
-- different sort direction.
SELECT /*+ REPARTITION(zip_code) */ name, age, zip_code FROM person
SORT BY name ASC, age DESC;
+--------+----+--------+
| name| age|zip_code|
+--------+----+--------+
| Anil K| 27| 94588|
| Dan Li| 18| 94588|
| John V|null| 94588|
| Zen Hui| 50| 94588|
|Aryan B.| 18| 94511|
| David K| 42| 94511|
|Lalit B.|null| 94511|
+--------+----+--------+