MAX_BY

描述

MAX_BY 函数用于根据指定列的最大值，返回对应的的关联值。

语法

MAX_BY(<expr1>, <expr2>)

参数说明

参数	说明
<expr1>	用于指定对应关联的表达式，支持类型为 Bool, TinyInt，SmallInt，Int，BigtInt，LargeInt，Float，Double，Decimal, String, Date, Datetime, Array, Map, Struct。
<expr2>	用于指定最大值统计的表达式，支持类型为 Bool, TinyInt，SmallInt，Int，BigtInt，LargeInt，Float，Double，Decimal, String, Date, Datetime, Array。

返回值

返回与输入表达式 相同的数据类型。 如果组内没有合法数据，则返回 NULL 。

举例

-- setup
create table tbl(
    k1 int,
    k2 int,
    arr ARRAY<INT>,
    mp MAP<STRING, INT>,
    st STRUCT<a: INT, b: STRING>,
) distributed by hash(k1) buckets 1
properties ("replication_num"="1");
insert into tbl values
    (0, 100, [1,2,3], {"x": 1, "y": 4}, NAMED_STRUCT("a", 1, "b", "x")),
    (1, 4,   [5, 6],  {"x": 2, "y": 3}, NAMED_STRUCT("a", 2, "b", "y")),
    (4, 1,   [7],     {"x": 3, "y": 2}, NAMED_STRUCT("a", 3, "b", "z")),
    (3, 1,   [8],     {"x": 4, "y": 1}, NAMED_STRUCT("a", 4, "b", "r"));

select max_by(k1, k2) from tbl;

+----------------+
| max_by(k1, k2) |
+----------------+
|              0 |
+----------------+

select max_by(arr, k1), max_by(mp, k1), max_by(st, k1) from tbl;

+-----------------+----------------+------------------+
| max_by(arr, k1) | max_by(mp, k1) | max_by(st, k1)   |
+-----------------+----------------+------------------+
| [7]             | {"x":3, "y":2} | {"a":3, "b":"z"} |
+-----------------+----------------+------------------+

select max_by(k1, arr), max_by(mp, arr), max_by(st, arr), max_by(arr, arr) from tbl;

+-----------------+-----------------+------------------+------------------+
| max_by(k1, arr) | max_by(mp, arr) | max_by(st, arr)  | max_by(arr, arr) |
+-----------------+-----------------+------------------+------------------+
|               3 | {"x":4, "y":1}  | {"a":4, "b":"r"} | [8]              |
+-----------------+-----------------+------------------+------------------+

select max_by(k1, k2) from tbl where k1 is null;

+----------------+
| max_by(k1, k2) |
+----------------+
|           NULL |
+----------------+