[MySQL]WEIGHT_STRING()

MySQL 문자열 함수와 연산자

 

WEIGHT_STRING()

   -

 

WEIGHT_STRING(str [AS {CHAR | BINARY} (N)] [flags])

의 형태

 

This function returns the weight string for the input string. The return value is a binary string that represents the comparison and sorting value of the string. It has these properties :

 

• If WEIGHT_STRING(str1) = WEIGHT_STRING(str2), then str1 = str2(str1 and str2 are considered equal)
• If WEIGHT_STRING(str1) < WEIGHT_STRING(str2), then str1 < str2(str1 sorts before str2)

WEIGHT_STRING() is a debugging function intended for internal use. Its behavior can change without notice between MySQL versions. It can be used for testing and debugging of collations, espcially if you are adding a new collation. 

(MySQL 8. xx 기준)

 

This list briefly summarizes the arguments. More details are given in the discussion following the list.

• str : The input string expression.
• As clause : Optinal; cast the input string to a given type and length.
• flags : Optional; unused.

The input string, str, is a string expression. If the input is a nonbinary (character) string such as a CHAR, VARCHAR, or TEXT value, the return value contains the collation weights for the string. If the input is a binary(byte) string such as a BINARY, VARBINARY, or BLOB value, the return value is the same as the input(the weight for each byte in a binary string is the byte value). If the input is NULL, WEIGHT_STRING() returns NULL.

 

 

mysql> SET @s = _utf8mb4 'AB' COLLATE utf8mb4_0900_ai_ci ;
Query OK, 0 rows affected (0.00 sec)

mysql> SELECT @s, HEX(@s), HEX(WEIGHT_STRING(@s)) ;
+------+---------+------------------------+
| @s   | HEX(@s) | HEX(WEIGHT_STRING(@s)) |
+------+---------+------------------------+
| AB   | 4142    | 1C471C60               |
+------+---------+------------------------+
1 row in set (0.01 sec)

mysql> SET @s = _utf8mb4 'ab' COLLATE utf8mb4_0900_ai_ci ;
Query OK, 0 rows affected (0.00 sec)

mysql> SELECT @s, HEX(@s), HEX(WEIGHT_STRING(@s)) ;
+------+---------+------------------------+
| @s   | HEX(@s) | HEX(WEIGHT_STRING(@s)) |
+------+---------+------------------------+
| ab   | 6162    | 1C471C60               |
+------+---------+------------------------+
1 row in set (0.00 sec)

mysql> SET @s = CAST('AB' AS BINARY );
Query OK, 0 rows affected (0.00 sec)

mysql> SELECT @s, HEX(@s), HEX(WEIGHT_STRING(@s));
+------+---------+------------------------+
| @s   | HEX(@s) | HEX(WEIGHT_STRING(@s)) |
+------+---------+------------------------+
| AB   | 4142    | 4142                   |
+------+---------+------------------------+
1 row in set (0.00 sec)

mysql> SET @s = CAST('ab' AS BINARY) ;
Query OK, 0 rows affected (0.00 sec)

mysql> SELECT @s, HEX(@s), HEX(WEIGHT_STRING(@s));
+------+---------+------------------------+
| @s   | HEX(@s) | HEX(WEIGHT_STRING(@s)) |
+------+---------+------------------------+
| ab   | 6162    | 6162                   |
+------+---------+------------------------+
1 row in set (0.00 sec)

mysql>