transform_keys
Description
Transforms keys in a map using a Lambda expression and produces a new key for each entry in the map.
This function is supported from v3.1 onwards.
Syntax
MAP transform_keys(lambda_func, any_map)
lambda_func
can also be placed after any_map
:
MAP transform_keys(any_map, lambda_func)
Parameters
-
any_map
: the Map. -
lambda_func
: the Lambda expression you want to apply toany_map
.
Return value
Returns a map value where the data types of keys are determined by the result of the Lambda expression and the data types of values are the same as values in any_map
.
If any input parameter is NULL, NULL is returned.
If a key or value in the original map is NULL, NULL is processed as a normal value.
The Lambda expression must have two parameters. The first parameter represents the key. The second parameter represents the value.
Examples
The following example uses map_from_arrays to generate a map value {1:"ab",3:"cdd",2:null,null:"abc"}
. Then the Lambda expression is applied to each key to increment the key by 1.
mysql> select transform_keys((k,v)->(k+1), col_map) from (select map_from_arrays([1,3,null,2,null],['ab','cdd',null,null,'abc']) as col_map)A;
+------------------------------------------+
| transform_keys((k, v) -> k + 1, col_map) |
+------------------------------------------+
| {2:"ab",4:"cdd",3:null,null:"abc"} |
+------------------------------------------+