The answer depends a great deal on how well organized your data is and the query itself.
For example, look at the query you have in the question:
SELECT rank, COUNT(id) FROM tablename GROUP BY rank
The first thing I think about with this query is whether the table is properly indexed.
OBSERVATION #1
If tablename had no indexes, a full table scan would be required.
OBSERVATION #2
If tablename had an index on rank, you still get a full table scan because of the MySQL Query Optimizer ruling out the use of the index because of factors such as key distribution and the possibility of having to lookup each id for every rank during a full index scan.
OBSERVATION #3
If the table had a compound index of (rank,id), then you can a full index scan. In most cases, a full index scan that never references the table for non-indexed columns would be faster than a full index scan that does (See OBSERVATION #2)
OBSERVATION #4
If the query was written slightly different
SELECT rank, COUNT(1) FROM tablename GROUP BY rank
then an index on just the rank column would suffice and produce a full index scan.
CONCLUSION
In light of these observtions, it is definitely a thing of beauty to present to the MySQL Query Optimizer two things:
- a good query
- proper indexes for all tables in the query
In retrospect, it is also good to give the MySQL Query Optimizer as much of an advantage upfront as possible.
This should do the trick for you:
DELIMITER $$
DROP TRIGGER IF EXISTS `employee_INSERT` $$
CREATE TRIGGER `employee_INSERT`
AFTER INSERT ON `employee`
FOR EACH ROW
BEGIN
INSERT INTO employee_tools (Id, Tool)
SELECT new.Id, tools.Tool_Name
FROM tools
WHERE tools.Division = new.Division;
END $$
DELIMITER ;
Best Answer