COERCIBILITY

Determine collation coercibility. This function returns a numeric value indicating the priority of the argument's collation in comparison operations.

Syntax

COERCIBILITY(str)

Description

Returns the collation coercibility value of the string argument. Coercibility defines what will be converted to what in case of collation conflict, with an expression with higher coercibility being converted to the collation of an expression with lower coercibility.

Coercibility	Description	Example
0	Explicit	Value using a COLLATE clause
1	No collation	Concatenated strings using different collations
2	Implicit	A string data type column value, CAST to a string data type
3	System constant	DATABASE(), USER() return value
4	Coercible	Literal string
5	Numeric	Numeric and temporal values
6	Ignorable	NULL or derived from NULL

Examples

SELECT COERCIBILITY(_latin1 'abc' COLLATE latin1_swedish_ci);
+-----------------------------------------------+
| COERCIBILITY(_latin1 'abc' COLLATE latin1_swedish_ci) |
+-----------------------------------------------+
|                                             0 |
+-----------------------------------------------+

CREATE TABLE t (a VARCHAR(30) COLLATE uca1400_swedish_ai_ci, b VARCHAR(30) COLLATE uca1400_german2_ai_ci) CHARSET utf8mb4;
INSERT INTO t VALUES ('abc', 'def'); /* a 2 coercibility */
SELECT COERCIBILITY(CONCAT(a, b)) FROM t;
+----------------------------+
| COERCIBILITY(CONCAT(a, b)) |
+----------------------------+
|                          1 |
+----------------------------+

SELECT COERCIBILITY(CAST(1 AS CHAR));
+-------------------------------+
| COERCIBILITY(CAST(1 AS CHAR)) |
+-------------------------------+
|                             2 |
+-------------------------------+

SELECT COERCIBILITY(USER());
+----------------------+
| COERCIBILITY(USER()) |
+----------------------+
|                    3 |
+----------------------+

SELECT COERCIBILITY('abc');
+---------------------+
| COERCIBILITY('abc') |
+---------------------+
|                   4 |
+---------------------+

SELECT COERCIBILITY(1);
+-----------------+
| COERCIBILITY(1) |
+-----------------+
|               5 |
+-----------------+

SELECT COERCIBILITY(NULL);
+--------------------+
| COERCIBILITY(NULL) |
+--------------------+
|                  6 |
+--------------------+

_{This page is licensed: GPLv2, originally from fill_help_tables.sql}