Removes duplicate elements from an array and returns a new array containing unique elements. The function maintains the original order of elements, keeping only the first occurrence of each element.
array_distinct(ARRAY<T> arr)
arr：ARRAY<T> type, the array to deduplicate. Supports column names or constant values.T supported types:
Return type: ARRAY<T>
Return value meaning:
Usage notes:
Query examples:
Integer array deduplication, the original array [1, 2, 3, 4, 5] has no duplicate elements, so the result after deduplication is the same as the original array.
SELECT array_distinct([1, 2, 3, 4, 5]); +---------------------------------+ | array_distinct([1, 2, 3, 4, 5]) | +---------------------------------+ | [1, 2, 3, 4, 5] | +---------------------------------+
String array deduplication: removes duplicate string elements. In the original array [‘a’, ‘b’, ‘a’, ‘c’, ‘b’, ‘d’], ‘a’ appears twice (keeping the first occurrence), ‘b’ appears twice (keeping the first occurrence), after deduplication it becomes [“a”, “b”, “c”, “d”].
SELECT array_distinct(['a', 'b', 'a', 'c', 'b', 'd']); +------------------------------------------------+ | array_distinct(['a', 'b', 'a', 'c', 'b', 'd']) | +------------------------------------------------+ | ["a", "b", "c", "d"] | +------------------------------------------------+
Array containing null values: null elements will also be deduplicated, multiple nulls only keep one. In the original array [1, null, 2, null, 3, null], null appears three times, after deduplication only the first null is kept, resulting in [1, null, 2, 3].
SELECT array_distinct([1, null, 2, null, 3, null]); +---------------------------------------------+ | array_distinct([1, null, 2, null, 3, null]) | +---------------------------------------------+ | [1, null, 2, 3] | +---------------------------------------------+
IP type array deduplication: deduplication of IPv4 address array. In the original array [‘192.168.1.1’, ‘192.168.1.2’, ‘192.168.1.1’], ‘192.168.1.1’ appears twice, after deduplication only the first occurrence of the address is kept, resulting in [192.168.1.1, 192.168.1.2].
SELECT array_distinct(CAST(['192.168.1.1', '192.168.1.2', '192.168.1.1'] AS ARRAY<IPV4>)); +------------------------------------------------------------------------------------+ | array_distinct(CAST(['192.168.1.1', '192.168.1.2', '192.168.1.1'] AS ARRAY<IPV4>)) | +------------------------------------------------------------------------------------+ | ["192.168.1.1", "192.168.1.2"] | +------------------------------------------------------------------------------------+
IPv6 type array deduplication: deduplication of IPv6 address array. In the original array [‘2001:db8::1’, ‘2001:db8::2’, ‘2001:db8::1’], ‘2001:db8::1’ appears twice, after deduplication only the first occurrence of the address is kept, resulting in [2001:db8::1, 2001:db8::2].
SELECT array_distinct(CAST(['2001:db8::1', '2001:db8::2', '2001:db8::1'] AS ARRAY<IPV6>)); +------------------------------------------------------------------------------------+ | array_distinct(CAST(['2001:db8::1', '2001:db8::2', '2001:db8::1'] AS ARRAY<IPV6>)) | +------------------------------------------------------------------------------------+ | ["2001:db8::1", "2001:db8::2"] | +------------------------------------------------------------------------------------+
Empty array returns empty array: empty array has no elements to deduplicate, directly returns empty array.
+--------------------+ | array_distinct([]) | +--------------------+ | [] | +--------------------+
NULL array returns NULL: returning NULL when the input array is NULL without throwing an error.
+----------------------+ | array_distinct(NULL) | +----------------------+ | NULL | +----------------------+
Single element array returns the original array: array with only one element has no duplicate elements, the result after deduplication is the same as the original array.
SELECT array_distinct([42]); +----------------------+ | array_distinct([42]) | +----------------------+ | [42] | +----------------------+
Complex types not supported:
Nested array type not supported, throws error.
SELECT array_distinct([[1,2,3], [4,5,6], [1,2,3]]); ERROR 1105 (HY000): errCode = 2, detailMessage = (10.16.10.6)[RUNTIME_ERROR]execute failed or unsupported types for function array_distinct(Array(Nullable(Array(Nullable(TINYINT)))))
Map type not supported, throws error.
SELECT array_distinct([{'a':1}, {'b':2}, {'a':1}]); ERROR 1105 (HY000): errCode = 2, detailMessage = (10.16.10.6)[RUNTIME_ERROR]execute failed or unsupported types for function array_distinct(Array(Nullable(Map(Nullable(String), Nullable(TINYINT)))))
Struct type not supported, throws error.
SELECT array_distinct(array(named_struct('name','Alice','age',20), named_struct('name','Bob','age',30), named_struct('name','Alice','age',20))); ERROR 1105 (HY000): errCode = 2, detailMessage = (10.16.10.6)[RUNTIME_ERROR]execute failed or unsupported types for function array_distinct(Array(Nullable(Struct(name:Nullable(String), age:Nullable(TINYINT)))))
Incorrect number of parameters will cause an error: the array_distinct function only accepts one array parameter, passing multiple parameters will cause an error.
SELECT array_distinct([1, 2, 3], [4, 5, 6]); ERROR 1105 (HY000): errCode = 2, detailMessage = Can not found function 'array_distinct' which has 2 arity. Candidate functions are: [array_distinct(Expression)]
Passing non-array type will cause an error: the array_distinct function only accepts array type parameters, passing non-array types like strings will cause an error.
SELECT array_distinct('not_an_array'); ERROR 1105 (HY000): errCode = 2, detailMessage = Can not find the compatibility function signature: array_distinct(VARCHAR(12))
ARRAY, DISTINCT, ARRAY_DISTINCT