Syntax:
LOWER(str)

Returns the string str with all characters changed to lowercase
according to the current character set mapping. The default is latin1
(cp1252 West European).

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

LOWER() (and UPPER()) are ineffective when applied to binary strings
(BINARY, VARBINARY, BLOB). To perform lettercase conversion, convert
the string to a nonbinary string:

mysql> SET @str = BINARY 'New York';
mysql> SELECT LOWER(@str), LOWER(CONVERT(@str USING latin1));
+-------------+-----------------------------------+
| LOWER(@str) | LOWER(CONVERT(@str USING latin1)) |
+-------------+-----------------------------------+
| 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, utf8_unicode_520_ci works according to UCA
5.2.0, whereas utf8_unicode_ci works according to UCA 4.0.0. See
http://dev.mysql.com/doc/refman/5.7/en/charset-unicode-sets.html.

URL: http://dev.mysql.com/doc/refman/5.7/en/string-functions.html

