---

{ “title”: “MAX_BY”, “language”: “en”, “description”: “The MAXBY function returns the associated value based on the maximum value of the specified column.” }

Description

The MAX_BY function returns the associated value based on the maximum value of the specified column.

When <expr2> is an Array, arrays are compared lexicographically, element by element; a NULL element is greater than any non-NULL element. A NULL array value is ignored.

Version difference: In the Doris 4.1 series since 4.1.5, and in Doris 4.2 and later, a NULL element inside an array compares greater than a non-NULL element. In Doris 4.0 and Doris 4.1 before 4.1.5, a NULL array element compares smaller. A NULL array value is ignored in all these versions.

Syntax

MAX_BY(<expr1>, <expr2>)

Parameters

Parameter	Description
<expr1>	The expression for the associated value, supports types: Bool, TinyInt, SmallInt, Int, BigInt, LargeInt, Float, Double, Decimal, String, Date, Datetime, TimestampNs, Array, Map, Struct.
<expr2>	The expression for the maximum value, supports types: Bool, TinyInt, SmallInt, Int, BigInt, LargeInt, Float, Double, Decimal, String, Date, Datetime, TimestampNs, Array.

Return Value

Returns the same data type as . Returns NULL if there is no valid data in the group.

Example

-- 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"));

Table created and data inserted successfully.

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 |
+----------------+

The following array comparison example applies to the Doris 4.1 series since 4.1.5, and to Doris 4.2 and later.

SELECT max_by(label, sort_key) AS result
FROM (
    SELECT 'null element' AS label, [1, NULL] AS sort_key
    UNION ALL SELECT 'non-null element', [1, 2]
    UNION ALL SELECT 'null array', CAST(NULL AS ARRAY<INT>)
) t;

null element

SELECT max_by(1, CAST(NULL AS ARRAY<INT>)) AS result;

NULL