我可以不逐行验证mysql模式吗

Question

I have a program that uses a local database. Users have different versions of the program, which in turn has a command to update their database. So now I have this huge block of code that looks like:

try
{
  using (var cmd = new MySqlCommand("ALTER TABLE `SomeTable` ADD COLUMN `SomeColumn` double NULL  ;", con))
                {
                    cmd.CommandType = CommandType.Text;
                    cmd.ExecuteNonQuery();
                } 
}

I have hundreds of these that add or drop columns, add tables, create indexes, etc. Is there a more efficient way of doing this, like verifying the entire schema at once, or am I stuck maintaining it? I do intend to change it to an array of strings and just run all the strings in the array, but I didn't know if there was a better way to do this.

Answer 1

You can query the whole schema in the database at once from the database information_schema . So you can verify all columns settings with one query. You can parse the result and check which updates are needed. (The database information_schema is specific for MySQL):

SELECT * FROM `information_schema`.`COLUMNS` WHERE TABLE_SCHEMA = "<your_database>"

For the future keep it easy an create a table like dbversion within the database. This table is holding the database version as an arbitrary string (eg "1.1.2") and the date, when the update was performed on this database. So you can query what schema version the database is and do your update if necessary.

Do the update of this database only if all updates where performed successfully. Another way is to insert a dataset before the update as semaphore that the update is in progress.

Eg version = "1.1.3 updating" and after the update was successful delete this added row and add version = "1.1.3".

CREATE TABLE `dbversion` (
  `date` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
  `version` varchar(50) NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

ALTER TABLE `dbversion`
  ADD PRIMARY KEY (`date`,`version`),
  ADD KEY `date` (`date`);

Get the newest entry with in dbversion :

SELECT * FROM `dbversion` ORDER BY `date` DESC LIMIT  1;