MariaDB starting with 10.0.5

The WEIGHT_STRING function was introduced in MariaDB 10.0.5.

Syntax

WEIGHT_STRING(str [AS {CHAR|BINARY}(N)] [LEVEL levels] [flags])
  levels: N [ASC|DESC|REVERSE] [, N [ASC|DESC|REVERSE]] ... 

Description

Returns a binary string representing the string's sorting and comparison value. A string with a lower result means that for sorting purposes the string appears before a string with a higher result.

WEIGHT_STRING() is particularly useful when adding new collations, for testing purposes.

If str is a non-binary string (CHAR, VARCHAR or TEXT), WEIGHT_STRING returns the string's collation weight. If str is a binary string (BINARY, VARBINARY or BLOB), the return value is simply the input value, since the weight for each byte in a binary string is the byte value.

WEIGHT_STRING() returns NULL if given a NULL input.

The optional AS clause permits casting the input string to a binary or non-binary string, as well as to a particular length.

AS BINARY(N) measures the length in bytes rather than characters, and right pads with 0x00 bytes to the desired length.

AS CHAR(N) measures the length in characters, and right pads with spaces to the desired length.

N has a minimum value of 1, and if it is less than the length of the input string, the string is truncated without warning.

The optional LEVEL clause specifies that the return value should contain weights for specific collation levels. The levels specifier can either be a single integer, a comma-separated list of integers, or a range of integers separated by a dash (whitespace is ignored). Integers can range from 1 to a maximum of 6, dependent on the collation, and need to be listed in ascending order.

If the LEVEL clause is no provided, a default of 1 to the maximum for the collation is assumed.

If the LEVEL is specified without using a range, an optional modifier is permitted.

ASC, the default, returns the weights without any modification.

DESC returns bitwise-inverted weights.

REVERSE returns the weights in reverse order.

Examples

The examples below use the HEX() function to represent non-printable results in hexadecimal format.

SELECT HEX(WEIGHT_STRING('x'));
+-------------------------+
| HEX(WEIGHT_STRING('x')) |
+-------------------------+
| 0058                    |
+-------------------------+

SELECT HEX(WEIGHT_STRING('x' AS BINARY(4)));
+--------------------------------------+
| HEX(WEIGHT_STRING('x' AS BINARY(4))) |
+--------------------------------------+
| 78000000                             |
+--------------------------------------+

SELECT HEX(WEIGHT_STRING('x' AS CHAR(4)));
+------------------------------------+
| HEX(WEIGHT_STRING('x' AS CHAR(4))) |
+------------------------------------+
| 0058002000200020                   |
+------------------------------------+

SELECT HEX(WEIGHT_STRING(0xaa22ee LEVEL 1));
+--------------------------------------+
| HEX(WEIGHT_STRING(0xaa22ee LEVEL 1)) |
+--------------------------------------+
| AA22EE                               |
+--------------------------------------+

SELECT HEX(WEIGHT_STRING(0xaa22ee LEVEL 1 DESC));
+-------------------------------------------+
| HEX(WEIGHT_STRING(0xaa22ee LEVEL 1 DESC)) |
+-------------------------------------------+
| 55DD11                                    |
+-------------------------------------------+

SELECT HEX(WEIGHT_STRING(0xaa22ee LEVEL 1 REVERSE));
+----------------------------------------------+
| HEX(WEIGHT_STRING(0xaa22ee LEVEL 1 REVERSE)) |
+----------------------------------------------+
| EE22AA                                       |
+----------------------------------------------+

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