BITMAP_HASH64 Function

bitmap_hash64(expr)

Overview

The BITMAP_HASH64 function hashes an input string using 64-bit hashing and returns a bitmap containing the hash value. This function is the 64-bit variant of BITMAP_HASH, using the MurmurHash3 64-bit algorithm to compute hash values. It produces a larger range of hash values, thereby reducing the probability of hash collisions.

Syntax

bitmap_hash64(expr)

Parameters

• expr: An expression of type STRING, the input string for which to compute a 64-bit hash value.

Return Result

Returns BITMAP type containing a 64-bit integer hash value.

Examples

1. Compute a 64-bit hash for a string:

   SELECT bitmap_to_string(bitmap_hash64('hello'));
   +------------------------------------------+
   | bitmap_to_string(bitmap_hash64('hello'))  |
   +------------------------------------------+
   | -8014657081559513573                      |
   +------------------------------------------+
   

2. Compute a 64-bit hash for another string:

   SELECT bitmap_to_string(bitmap_hash64('world'));
   +------------------------------------------+
   | bitmap_to_string(bitmap_hash64('world'))  |
   +------------------------------------------+
   | -5394866185914414384                      |
   +------------------------------------------+
   

3. When the input is NULL:

   SELECT bitmap_hash64(NULL);
   +---------------------+
   | bitmap_hash64(NULL) |
   +---------------------+
   | NULL                |
   +---------------------+
   

Notes

• When the input parameter is NULL, the result is NULL.
• BITMAP_HASH64 uses the MurmurHash3 64-bit algorithm, while BITMAP_HASH uses the MurmurHash3 32-bit algorithm. The 64-bit hash produces a larger value range with a lower probability of hash collisions, making it suitable for large-scale data scenarios.
• The returned bitmap contains a single 64-bit unsigned integer hash value, which can be used directly for subsequent bitmap operations (such as BITMAP_OR, BITMAP_AND, etc.).