MAP_EXCEPT

Description

The MAP_EXCEPT function is used to remove key-value pairs (K, V) from the first map (map1) that are the same as those in the second map (map2). This function is very useful in data cleaning and transformation, helping users quickly filter out unnecessary duplicate data.

Parameters

• map1, map2: map<K, V> types, representing the first and second maps respectively.

Return Value

Returns a new map (map<K, V>) that contains the result of removing key-value pairs from the first map that are the same as those in the second map.

Example

1. Filter out duplicate key-value pairs

SELECT MAP_EXCEPT(MAP(1, 'apple', 2, 'orange'), MAP(1, 'apple', 3, 'banana'));
-- Return result: {2:'orange'}

In this example, the MAP_EXCEPT function removes the key-value pair (1, 'apple') from the first map that is the same as in the second map.

2. Retain unique key-value pairs

SELECT MAP_EXCEPT(MAP(1, 'apple', 2, 'orange', 3, 'banana'), MAP(2, 'orange', 4, 'grape'));
-- Return result: {1:'apple', 3:'banana'}

In this example, the MAP_EXCEPT function removes the key-value pair (2, 'orange') that is the same in the second map from the first map, while retaining other unique key-value pairs.

3. Handling NULL Values

SELECT MAP_EXCEPT(MAP(1, NULL, 2, 'pear'), MAP(1, NULL));
-- Return result: {2:'pear'}

In this example, the MAP_EXCEPT function removes the key-value pair (1, NULL) that is the same in the second map from the first map, while retaining other unique key-value pairs.

From the above example, you can see the flexibility and practicality of the MAP_EXCEPT function when dealing with map data. You can flexibly apply this function for data filtering and transformation according to your needs.