How to change mysql to mysqli?

The first thing to do would probably be to replace every mysql_* function call with its equivalent mysqli_*, at least if you are willing to use the procedural API — which would be the easier way, considering you already have some code based on the MySQL API, which is a procedural one.

To help with that, the MySQLi Extension Function Summary is definitely something that will prove helpful.

For instance:

• mysql_connect will be replaced by mysqli_connect
• mysql_error will be replaced by mysqli_error and/or mysqli_connect_error, depending on the context
• mysql_query will be replaced by mysqli_query
• and so on

Note: For some functions, you may need to check the parameters carefully: Maybe there are some differences here and there — but not that many, I’d say: both mysql and mysqli are based on the same library (libmysql ; at least for PHP <= 5.2)

For instance:

• with mysql, you have to use the mysql_select_db once connected, to indicate on which database you want to do your queries
• mysqli, on the other side, allows you to specify that database name as the fourth parameter to mysqli_connect.
• Still, there is also a mysqli_select_db function that you can use, if you prefer.

Once you are done with that, try to execute the new version of your script… And check if everything works ; if not… Time for bug hunting 😉