How Do I Use a User-Defined GaussDB(DWS) Function to Rewrite the CRC32() Function?
GaussDB(DWS) currently does not have a built-in CRC32() function. However, if you need to implement the CRC32() function in MySQL, you can rewrite it using a user-defined GaussDB(DWS) function.
- CRC32(expr)
- Description: Calculates the cyclic redundancy. The input parameter expr is a string. If the parameter is NULL, NULL is returned. Otherwise, a 32-bit unsigned value is returned after redundancy calculation.
Example of rewriting the CRC32() function using user-defined GaussDB(DWS) function statements:
CREATE OR REPLACE FUNCTION crc32(text_string text) RETURNS bigint AS $$DECLAREval bigint;i int;j int;byte_length int;binary_string bytea;BEGINIF text_string is null THENRETURN null;ELSIF text_string = '' THENRETURN 0;END IF;i = 0;val = 4294967295;byte_length = bit_length(text_string) / 8;binary_string = decode(replace(text_string, E'\\', E'\\\\'), 'escape');LOOPval = (val # get_byte(binary_string, i))::bigint;i = i + 1;j = 0;LOOPval = ((val >> 1) # (3988292384 * (val & 1)))::bigint;j = j + 1;IF j >= 8 THENEXIT;END IF;END LOOP;IF i >= byte_length THENEXIT;END IF;END LOOP;RETURN (val # 4294967295);END$$ IMMUTABLE LANGUAGE plpgsql;
Verify the rewriting result.
select crc32(null),crc32(''),crc32('1');crc32 | crc32 | crc32-------+-------+------------| 0 | 2212294583(1 row)
For how to use user-defined functions, see "CREATE FUNCTION" in Database Repository Service (DWS) SQL Syntax References.
Parent topic: Database Use