Hash Combine

HASH_COMBINE

Description

The hash_combine function is used to combine multiple hash values h1, h2, ..., hN into a new hash value. The characteristic of this function is that the order of the combined values will affect the final hash value.

The hash_combine_commutative function is similar to hash_combine, and is also used to combine multiple hash values h1, h2, ..., hN into a new hash value. The difference is that the order of the combined values does not affect the final hash value, satisfying the commutative property.

Parameter Description

h1, h2, ... hN: bigint type, representing the hash values to be combined.

Return Result

Returns a value of bigint type, representing the combined hash value.

Example

The following example demonstrates how to use the hash_combine and hash_combine_commutative functions:


-- Using the hash_combine function
SELECT hash_combine(1, 2, 3) AS hash_combine_result1;
-- Result: 175247765312

SELECT hash_combine(3, 2, 1) AS hash_combine_result2;
-- Result: 175247756320

-- Using the hash_combine_commutative function
SELECT hash_combine_commutative(1, 2, 3) AS hash_commutative_result1;
-- Result: 10777284388

SELECT hash_combine_commutative(3, 2, 1) AS hash_commutative_result2;
-- Result: 10777284388

From the above example, it can be seen that the hash_combine function changes the result when the order of the combined values changes; while the hash_combine_commutative function keeps the result unchanged when the order of the combined values changes.

Notes

When the number of combined hash values is small, these two functions can be used to merge the hash values. However, if a large number of hash values need to be merged, it is recommended to use other methods to avoid performance issues.
In practical applications, you can choose the appropriate function based on specific needs. If the order of the combined values matters, you can use the hash_combine function; if the order does not matter, you can use the hash_combine_commutative function.