LOWER

Syntax:
LOWER(str)

Returns the string str with all characters changed to lowercase
according to the current character set mapping. The default is utf8mb4.

mysql> SELECT LOWER('QUADRATICALLY');
-> 'quadratically'

LOWER() (and UPPER()) are ineffective when applied to binary strings
(BINARY, VARBINARY, BLOB). To perform lettercase conversion of a binary
string, first convert it to a nonbinary string using a character set
appropriate for the data stored in the string:

mysql> SET @str = BINARY 'New York';
mysql> SELECT LOWER(@str), LOWER(CONVERT(@str USING utf8mb4));
+-------------+------------------------------------+
| LOWER(@str) | LOWER(CONVERT(@str USING utf8mb4)) |
+-------------+------------------------------------+
| New York | new york |
+-------------+------------------------------------+

For collations of Unicode character sets, LOWER() and UPPER() work
according to the Unicode Collation Algorithm (UCA) version in the
collation name, if there is one, and UCA 4.0.0 if no version is
specified. For example, utf8mb4_0900_ai_ci and utf8_unicode_520_ci work
according to UCA 9.0.0 and 5.2.0, respectively, whereas utf8_unicode_ci
works according to UCA 4.0.0. See
https://dev.mysql.com/doc/refman/8.0/en/charset-unicode-sets.html.

URL: https://dev.mysql.com/doc/refman/8.0/en/string-functions.html