MySQL lower_case_table_names导致PHP连接错误

Question

In MySQL, the lower_case_table_names global variable determines whether letter case is preserved when a table name is written to disk, and whether matching of table names is case sensitive. According to the docs :

If you are using InnoDB or MySQL Cluster (NDB) tables, you should set this variable to 1 on all platforms to force names to be converted to lowercase.

My site is on a Apache 2.4 with MySQL 5.6.23 and PHP 5.5.25. Most of my tables are MyISAM but I would like to convert them to InnoDB. In accordance with the directive above, I tried to set lower_case_table_names=1 in MySQL's config file. However, after restarting the server, I can no longer connect to the database from my PHP code using the mysqli extension. The code $this->mysqli = new \\mysqli($host,$user,$pwd,$db_name,$port); returns mysqli->connect_error = "Access denied for user 'username'@'localhost' (using password: YES)" . I am certain that the login credentials are good for the following reasons:

• Outside of the PHP environment, I can connect to the database using the same credentials, with a remote tool (SQLyog).
• If I remove lower_case_table_names=1 line from the config file and restart the server, things work again.

During the MySQL server startup sequence -- when lower_case_table_names=1 -- the error log shows 3 warnings:

• [Warning] TIMESTAMP with implicit DEFAULT value is deprecated. Please use --explicit_defaults_for_timestamp server option (see documentation for more details).
• [Warning] 'db' entry '%_ldap_ou=addressbook cpldap@localhost' had database in mixed case that has been forced to lowercase because lower_case_table_names is set. It will not be possible to remove this privilege using REVOKE.
• [Warning] 'db' entry 'logaholicdb_host logaholic@localhost' had database in mixed case that has been forced to lowercase because lower_case_table_names is set. It will not be possible to remove this privilege using REVOKE.

There are also several [Note] entries logged under both configs. When the lower_case_table_names=1 line is removed, only the 1st warning appears. The user getting denied access has the following privileges on the database in question (result of SHOW GRANTS FOR 'username'@'localhost'; )

• GRANT USAGE ON . TO 'username'@'localhost' IDENTIFIED BY PASSWORD '*6DF294D9BAA539074CFC4DD08E77909FE53CFCE1'
• GRANT SELECT, INSERT, UPDATE, DELETE, CREATE, DROP, REFERENCES, INDEX, ALTER, CREATE TEMPORARY TABLES, LOCK TABLES, EXECUTE, CREATE VIEW, SHOW VIEW, CREATE ROUTINE, ALTER ROUTINE ON my_db .* TO 'username'@'localhost'

Why is the connection failing and how can I fix it?

Answer 1

Step1: First take backup of your db (all tales) by mysqldump command.

Step2: Now change your configuration setting for lower case.

Step3: Now restart mysql service.

Step4: Now restore the backup.

By this all tables name written on disk in lower case by default and even you can call them either by lower/upper/camel case but actually they will be stored on server in lower case.

Answer 2

Upon further research, here is what I've found.

The problem breaking my site was not actually with establishing a connection to MySQL. The error that denied me access earlier was caused by another issue. My debugging session was querying a development database with different access permissions, so when debugging the problem I thought the failed connection was the cause -- it was a problem with the debugging itself. Something else was actually breaking my site.

Eventually I figured out that setting lower_case_table_names=1 seems to break SQL query execution on any table whose name has a capital letter. For instance, I have a table named tblCountries . If I run query SELECT * FROM tblCountries , MySQL returns error tblcountries does not exist . Notice the error has lowercase 'c'.

Queries on a table name with no upper case seem to work just fine: SELECT * FROM user works because that table name ( user ) has no uppercase. So I tried renaming tblCountries to tblcountries with query RENAME TABLE 'tblCountries' to 'tblcountries' but MySQL failed with error Can't find file: './db_name/tblcountries.frm' (errno: 2 - No such file or directory) .

Both of these issues seem to suggest that the server is putting everything in lower case before running the query. In fact, on disc although there is no file tblcountries.frm , the file tblCountries.frm exists along with files tblCountries.MYD and tblCountries.MYI . If I manually rename all three files by replacing 'C' with 'c', the same query SELECT * FROM tblCountries executes successfully.

So I have at least two options but don't know which is better or if there is a 3rd best option:

1) remove lower_case_table_names=1 option to make the server respect letter case when executing queries; then execute RENAME TABLE 'tblCountries' to 'tblcountries' with every table to remove all uppercases; finally when all uppercases have been removed, re-insert lower_case_table_names=1 .

2) Just manually rename files on disk as I did with tblCountries.frm . This seems like the easier method but I don't know enough about MySQL to know whether it will cause me more problems down the line.