Built-in character set parsing for DATE_FORMATE function in MySQL _ MySQL

MySQL DATE_FORMATE function built-in character set parsing bitsCN.com

Today, I helped my colleagues handle an SQL statement (simplified) and reported the following error:

The code is as follows:
Mysql> select date_format ('2017-11-19 ', 'Y-m-D')> timediff ('2017-11-19', '2017-11-20 ');

ERROR 1267 (HY000): Illegal mix of collations (utf8_general_ci, COERCIBLE) and (latin1_swedish_ci, NUMERIC) for operation '>'

At first glance, it was quite inexplicable. I checked the manual and found that there was such a paragraph:

The language used for day and month www.111cn.net names and abbreviations is controlled by the value of the lc_time_names system variable (Section 9.7, "MySQL Server Locale Support ").

The DATE_FORMAT () returns a string with a character set and collation given by character_set_connection and collation_connection so that it can return month and weekday names containing non-ASCII characters.

That is to say, the result returned by the DATE_FORMATE () function carries the character set/verification set attribute, while the TIMEDIFF () function does not have the character set/verification set attribute. let's verify it:

The code is as follows:
Mysql> set names utf8;
Mysql> select charset (date_format ('2017-11-19 ', 'Y-m-D'), charset (timediff ('2017-11-19 ', '2017-11-20 '));
+ -------------------------------------------- + ------------------------------------------------- +
| Charset (date_format ('2017-11-19 ', 'Y-m-D') | charset (timediff ('2017-11-19', '2017-11-20 ') |
+ -------------------------------------------- + ------------------------------------------------- +
| Utf8 | binary |
+ -------------------------------------------- + ------------------------------------------------- +

Mysql> set names gb2312;
Mysql> select charset (date_format ('2017-11-19 ', 'Y-m-D'), charset (timediff ('2017-11-19 ', '2017-11-20 '));
+ -------------------------------------------- + ------------------------------------------------- +
| Charset (date_format ('2017-11-19 ', 'Y-m-D') | charset (timediff ('2017-11-19', '2017-11-20 ') |
+ -------------------------------------------- + ------------------------------------------------- +
| Gb2312 | binary |
+ -------------------------------------------- + ------------------------------------------------- +

As you can see, the character SET returned by the DATE_FORMAT () function varies with the character_set_connection and collation_connection values modified through set names. In this case, if you want to work properly, you need to convert the result into a character set. for example:

The code is as follows:
Mysql> select date_format ('2017-11-19 ', 'Y-m-D')> convert (timediff ('2017-11-19', '2017-11-20 ') using utf8 );
+ Shards +
| Date_format ('2017-11-19 ', 'Y-m-D')> convert (timediff ('2017-11-19', '2017-11-20 ') using utf8) |
+ Shards +
| 1 |
+ Shards +

You can.

P.S, MySQL versions: 5.5.20-55-log Percona Server (GPL), Release rel24.1, Revision 217

Appendix

The following describes the function parameters:
% S, % s two-digit second (,..., 59)
% I two-digit score (,..., 59)
% H two-digit hour, 24 hours (,..., 23)
% H, % I two-digit hour, 12 hours (,..., 12)
% K, 24 hours (0, 1,..., 23)
% L hour in numeric format (1, 2,..., 12)
% T 24-hour time format (hh: mm: s)
% R 12-hour time format (hh: mm: ss AM or hh: mm: ss PM)
% P AM or P M
% W name of each day in a week (Sunday, Monday,..., Saturday)
% A abbreviation of the name of each day in a week (Sun, Mon,..., Sat)
% D indicates the number of days in a month (00, 01,..., 31)
% E indicates the number of days in a month (1, 2,..., 31)
% D indicates the number of days in a month (1st, 2nd, 3rd ,...)
% W represents the number of days in a week (0 = Sunday, 1 = Monday,..., 6 = Saturday)
% J represents the number of days in a year in three digits (001,002,..., 366)
% U week (0, 1, 52), where Sunday is the first day of the week
% U week (0, 1, 52), where Monday is the first day of the week
% M month name (January, February,..., December)
% B abbreviated month name (January, February,..., December)
% M double-digit month (01, 02,..., 12)
% C indicates the month (1, 2,..., 12)
The year in the format of % Y.
The year in double-digit % y format.
% Direct value "%"

For more details, see: http://www.111cn.net/database/mysql/56671.htm

BitsCN.com