MySQL

1. Syntax

alter table Airline add unique key code (code);
alter table Airline drop key code;

2. innodb_file_per_table

Each table will have its own tablespace instead of using a common tablespace. This is useful if you are low on space - you can drop at table and disk space will be reclaimed. If you are using a common tablespace then its not possible. Usually database servers are allocated space beforehand, so this is more of a developer setup. If you were to do this on production I'm unsure of the performance impacts.

Add "innodb_file_per_table" to my.ini on a line by itself.

3. Scripting

mysql client password can be communicated by exporting the MYSQL_PWD environment variable.

4. The MySQL Query Cache

Docs at The MySQL Query Cache.

The command "show global status" will give you a snapshot of the server. http://dev.mysql.com/doc/refman/5.1/en/server-status-variables.html

Variables to do with the query cache are

Qcache_lowmem_prunes may indicate that your cache is too small.

If a query result is returned from query cache, the server increments the Qcache_hits status variable, not Com_select. If it misses the cache and has to evaluate the select statement, it will increment Com_select.

I calculate the hit percentage as Qcache_hits / (Qcache_hits + Com_select)