MAP_FROM_ARRAYS function to create a map from arrays - MaxCompute

Builds a MAP from two arrays: one for keys and one for values.

Syntax

map<K, V> map_from_arrays([string <mapDupKeyPolicy>,] array<K> <a>, array<V> <b>))

Parameters

Parameter	Required	Type	Description
`mapDupKeyPolicy`	No	STRING	How to handle duplicate keys. Valid values: `exception` (returns an error) and `last_win` (the last occurrence overwrites earlier ones). Defaults to `last_win` if neither this parameter nor `odps.sql.map.key.dedup.policy` is set.
`a`	Yes	`array<K>`	The key array. `K` can be any data type.
`b`	Yes	`array<V>`	The value array. `V` can be any data type.

Return value

Returns a value of the MAP type.

If a or b is null, returns null.
If a and b have different lengths, returns an error.
If a contains a null element, returns an error.

Usage notes

Duplicate key policy

Two mechanisms control how MAP_FROM_ARRAYS handles duplicate keys, applied in this order:

The mapDupKeyPolicy parameter in the function call.
The odps.sql.map.key.dedup.policy session-level setting, used when mapDupKeyPolicy is not specified.

If neither is set, the default policy is last_win.

To set the session-level policy:

set odps.sql.map.key.dedup.policy=exception;

Examples

Basic usage

-- Returns {1:2, 3:4}
SELECT map_from_arrays(array(1.0, 3.0), array('2', '4'));

Handling duplicate keys with `last_win`

When the key array contains duplicates, last_win keeps the value from the last occurrence.

-- Returns {1:2, 3:6}
-- The key 3 appears twice; last_win keeps '6' and discards '4'
SELECT map_from_arrays('last_win', array(1.0, 3.0, 3), array('2', '4', '6'));

Related functions

MAP_FROM_ARRAYS is a complex type function. For more information about functions that process ARRAY, MAP, STRUCT, and JSON data, see Complex type functions.