MySQL queries: two SELECT or one with LEFT Join?

Question

Is there any difference between two SELECTs from database or single SELECT with LEFT Join ?

I am limited by number of queries per hour and I am developing my own application.

"SELECT * FROM table" represents one query?

"SELECT * FROM table LEFT JOIN another_table ON table.column=another_table.column2'" represents one query too?

Are UPDATE , INSERT and DELETE considered query?

Thanks a lot. If my post is not ok, I can delete.

Answer 1

If you have limited number of queries, than LEFT JOIN is better, since it's only one query (one connection to database). And yes, UPDATE , INSERT , DELETE is queries too. But You can insert multiple entries with single query.

Answer 2

Yes, joining tables is one query. Splitting that query and executing separately will take more time.

Answer 3

LEFT JOIN is better, because it is only one query and need only one connection to database.

SELECT , UPDATE , DELETE and INSERT are all queries

Answer 4

It's almost always better to use less query than more, so in your case better to use join than run 2 queries.

However you should add indexes to table.column and another_table.column2 to make sure it won't affect your performance.

Of course all queries, also UPDATE , DELETE and INSERT are considered as queries, not only SELECT