This appendix describes several types of MySQL variables:
System variables that provide information about server configuration
System variables that exist in session-only form per client
Status variables that provide information about the server’s current operational state
User variables that you can define, assign values to, and refer to in expressions
Values for variables that represent buffer sizes or lengths generally are given in bytes. Exceptions are noted as necessary.
Unless otherwise indicated, the variables listed here have been present in MySQL at least as early as MySQL 5.0.0. Variables that were introduced or that changed in meaning since then are noted.
System variables ...