what is best location for close mysql connection in php ?

The question is true for all technology for example .NET, PHP etc. When required for execute any database command/query then you should open database connection and after getting result you should close that connection. Only problem area you can find that is connected resultset fetching issue. In .NET like datareader. You can not close connection until you finish to read datareader object. If same type of return object there in PHP then after finish to read that object then you close it. Always need to remember that database open connection time should as shorter as possible.