what are the changes in mysql 8 result rowset case?

问题

when running

SELECT maxlen FROM `information_schema`.`CHARACTER_SETS`;

mysql 5.7 and mysql 8 produce different results:

on mysql 5.7 the results row names are lower cased,
on mysql 8 the results row names are upper cased.

NB : in the CHARACTER_SETS table, the comumn name is MAXLEN (upper cased).

Since I can't find a resource documenting it, my question is :

what are the changes in mysql 8 result rowset case ?

回答1:

MySQL 8.0 did change the implementation of some views in the INFORMATION_SCHEMA:

https://mysqlserverteam.com/mysql-8-0-improvements-to-information_schema/ says:

Now that the metadata of all database tables is stored in transactional data dictionary tables, it enables us to design an INFORMATION_SCHEMA table as a database VIEW over the data dictionary tables. This eliminates costs such as the creation of temporary tables for each INFORMATION_SCHEMA query during execution on-the-fly, and also scanning file-system directories to find FRM files. It is also now possible to utilize the full power of the MySQL optimizer to prepare better query execution plans using indexes on data dictionary tables.

So it's being done for good reasons, but I understand that it has upset some of your queries when you fetch results in associative arrays based on column name.

You can see the definition of the view declares the column name explicitly in uppercase:

mysql 8.0.14> SHOW CREATE VIEW CHARACTER_SETS\G
*************************** 1. row ***************************
                View: CHARACTER_SETS
         Create View: CREATE ALGORITHM=UNDEFINED DEFINER=`mysql.infoschema`@`localhost` SQL SECURITY DEFINER VIEW `CHARACTER_SETS` AS 
  select 
    `cs`.`name` AS `CHARACTER_SET_NAME`,
    `col`.`name` AS `DEFAULT_COLLATE_NAME`,
    `cs`.`comment` AS `DESCRIPTION`,
    `cs`.`mb_max_length` AS `MAXLEN` -- delimited column explicitly uppercase
  from (`mysql`.`character_sets` `cs` 
  join `mysql`.`collations` `col` on((`cs`.`default_collation_id` = `col`.`id`)))

character_set_client: utf8
collation_connection: utf8_general_ci

You can work around the change in a couple of ways:

You can declare your own column aliases in the case you want when you query a view:

mysql 8.0.14> SELECT MAXLEN AS `maxlen` 
  FROM `information_schema`.`CHARACTER_SETS` LIMIT 2;
+--------+
| maxlen |
+--------+
|      2 |
|      1 |
+--------+

You could start a habit of querying columns in uppercase prior to 8.0. Here's a test showing results in my 5.7 sandbox:

mysql 5.7.24> SELECT MAXLEN 
  FROM `information_schema`.`CHARACTER_SETS` LIMIT 2;
+--------+
| MAXLEN |
+--------+
|      2 |
|      1 |
+--------+

Or you could fetch results into a non-associative array, and reference columns by column number, instead of by name.

回答2:

There is no change in case sensitivity. If you check mysql documentation on identifier case sensitivity, both v5.7 and v8.0 say that field names are case insensitive:

Column, index, stored routine, event, and resource group names are not case-sensitive on any platform, nor are column aliases.

To me this seems more like a display difference.

来源：https://stackoverflow.com/questions/54538448/what-are-the-changes-in-mysql-8-result-rowset-case

标签

mysql

case-sensitive

mysql-8.0