content_image/669869.jpg
STRCMP()  performs the comparison using the collation of the arguments. 

mysql> SET @s1 = _utf8mb4 ’x’ COLLATE utf8mb4_0900_ai_ci; mysql> SET @s2 = _utf8mb4 ’X’ COLLATE utf8mb4_0900_ai_ci; mysql> SET @s3 = _utf8mb4 ’x’ COLLATE utf8mb4_0900_as_cs; mysql> SET @s4 = _utf8mb4 ’X’ COLLATE utf8mb4_0900_as_cs; mysql> SELECT STRCMP(@s1, @s2), STRCMP(@s3, @s4); +------------------+------------------+ | STRCMP(@s1, @s2) | STRCMP(@s3, @s4) | +------------------+------------------+ | 0 | -1 | +------------------+------------------+ 

-> 0 

If the collations are incompatible, one of the arguments must be converted to be compatible with the other. See Section 10.8.4, “Collation Coercibility in Expressions” . 

mysql> SET @s1 = _utf8mb4 ’x’ COLLATE utf8mb4_0900_ai_ci; mysql> SET @s2 = _utf8mb4 ’X’ COLLATE utf8mb4_0900_ai_ci; mysql> SET @s3 = _utf8mb4 ’x’ COLLATE utf8mb4_0900_as_cs; mysql> SET @s4 = _utf8mb4 ’X’ COLLATE utf8mb4_0900_as_cs; --> mysql> SELECT STRCMP(@s1, @s3); ERROR 1267 (HY000): Illegal mix of collations (utf8mb4_0900_ai_ci,IMPLICIT) and (utf8mb4_0900_as_cs,IMPLICIT) for operation ’strcmp’ mysql> SELECT STRCMP(@s1, @s3 COLLATE utf8mb4_0900_ai_ci); +---------------------------------------------+ | STRCMP(@s1, @s3 COLLATE utf8mb4_0900_ai_ci) | +---------------------------------------------+ | 0 | +---------------------------------------------+ 

## 12.8.2 Regular Expressions 

<img src='content_image/669869.jpg'>

A regular expression is a powerful way of specifying a pattern for a complex search. This section discusses the functions and operators available for regular expression matching and illustrates, with examples, some of the special characters and constructs that can be used for regular expression operations. See also Section 3.3.4.7, “Pattern Matching” . 

MySQL implements regular expression support using International Components for Unicode (ICU), which provides full Unicode support and is multibyte safe. (Prior to MySQL 8.0.4, MySQL used Henry Spencer’s implementation of regular expressions, which operates in byte-wise fashion and is not multibyte safe. For information about ways in which applications that use regular expressions may be affected by the implementation change, see Regular Expression Compatibility Considerations.) 

