Returning Results to the Client

The final step in executing a query is to reply to the client. Even queries that don’t return a result set still reply to the client connection with information about the query, such as how many rows it affected.

If the query is cacheable, MySQL will also place the results into the query cache at this stage.

The server generates and sends results incrementally. Think back to the single-sweep multijoin method we mentioned earlier. As soon as MySQL processes the last table and generates one row successfully, it can and should send that row to the client.

This has two benefits: it lets the server avoid holding the row in memory, and it means the client starts getting the results as soon as possible.^[83]