Mysql – Renaming foreign-key columns in MySQL

If you want to disable all constraints in the database just run this code:

-- disable all constraints
EXEC sp_MSforeachtable "ALTER TABLE ? NOCHECK CONSTRAINT all"

To switch them back on, run: (the print is optional of course and it is just listing the tables)

-- enable all constraints
exec sp_MSforeachtable @command1="print '?'", @command2="ALTER TABLE ? WITH CHECK CHECK CONSTRAINT all"

I find it useful when populating data from one database to another. It is much better approach than dropping constraints. As you mentioned it comes handy when dropping all the data in the database and repopulating it (say in test environment).

If you are deleting all the data you may find this solution to be helpful.

Also sometimes it is handy to disable all triggers as well, you can see the complete solution here.

Timestamps in MySQL are generally used to track changes to records, and are often updated every time the record is changed. If you want to store a specific value you should use a datetime field.

If you meant that you want to decide between using a UNIX timestamp or a native MySQL datetime field, go with the native format. You can do calculations within MySQL that way ("SELECT DATE_ADD(my_datetime, INTERVAL 1 DAY)") and it is simple to change the format of the value to a UNIX timestamp ("SELECT UNIX_TIMESTAMP(my_datetime)") when you query the record if you want to operate on it with PHP.