查询视图时列名更改大小写

Question

The following test case describes my problem.

CREATE TABLE the_table (id INT, Title CHAR(10));
CREATE VIEW the_view AS SELECT * FROM the_table;
INSERT INTO the_table VALUES (1, 'Hello');

notice that 'Title' in capitalized

Now when I try:

SELECT id, title FROM the_table;

Result:
+------+-------+
| id   | title |
+------+-------+
|    1 | Hello |
+------+-------+

(notice how 'title' is lowercase in both the query and the result column)

BUT, when i do the same thing on the view:

SELECT id, title FROM the_view;

Result: 
+------+-------+
| id   | Title |
+------+-------+
|    1 | Hello |
+------+-------+

It is the same select clause, but this time the column name for 'Title' is Capitalized!

I am trying to reuse a code with a view of the exact same schema, but this messes it up.

I can't really find any reference whether this is standard MySQL behavior or not, but is there a way around it?

Answer 1

Unless you quote the column or table names, SQL is supposed to be case insensitive. Don't put quotes around you column and table names and you should not have problems. I have noticed some tools tend to quote the column and variable names.

Answer 2

This is standard MySQL behavior. MySQL uses those column names in the resultset that you use in the main query. Since column names are not case-sensitive in MySQL, it allows querying columns in whatever letter-case and use the same letter-case in the resultset.

Therefore, SELECT id, title FROM the_table; uses "id" and "title" in the resultset. Try running SELECT ID, TITLE FROM the_table; or SELECT Id, Title FROM the_table; and you'll see column names in respective cases.

With views, it uses the column names that are provided in the SELECT statement used when creating the view. In your case, it is SELECT * FROM the_table; . Hence when you run SELECT id, title FROM the_view; , it gives the column names as "id" and "Title".

However, if you create your view as CREATE VIEW the_view AS SELECT id, title FROM the_table; , using lowercase column names, you will see that the SELECT from view will also return the columns as "id" and "title".

I'm not familiar with the MySQL internals but I hope it makes sense.

Answer 3

If we query how the view is stored:

SHOW CREATE VIEW the_view

... we find a result that contains this:

CREATE ALGORITHM=UNDEFINED DEFINER=`test`@`%` SQL SECURITY DEFINER VIEW `the_view` AS select `the_table`.`id` AS `id`,`the_table`.`Title` AS `Title` from `the_table`

This happens as well if you replace * with a column list: MySQL adds an AS clause with an alias, which effectively hard-codes column names.

The conclusion is that a view is not a table. You'll need to create it with the exact case you want to use. Whatever, case is normally irrelevant unless your client language messes things up when case changes (eg PHP associative arrays).