I am testing my database design under load and I need to retrieve only a fixed number of rows (5000)
I can specify a LIMIT to achieve this, however it seems that the query builds the result set of all rows that match and then returns only the number of rows specified in the limit. Is that how it is implemented?
Is there a for MySQL to read one row, read another one and basically stop when it retrieves the 5000th matching row?
MySQL is smart in that if you specify a
LIMIT 5000in your query, and it is possible to produce that result without generating the whole result set first, then it will not build the whole result.For instance, the following query:
This query will need to scan the whole
tableunless there is an index oncolumn, in which case it does the smart thing and uses the index to find the rows with the smallestcolumn.