Re: Query speed and columns per table

[Rick James]

"Count the disk hits". And "count the bytes transferred".

Probably the CPU is not the gating issue, but rather disk I/O and/or network bandwidth.

Not a simple formula? Don't forget about caches, etc.

Factors involved:
* Disk hits -- more data -> more time
* Bytes in each column -- again more data -> more time; example: INT takes 4 bytes; TINYINT takes 1
* Padding in blocks (eg, from deleting records)
* Row overhead -- 100 rows with 10 columns takes more 'effort' than 10 rows with 100 columns.
* etc.

To assist in analyzing slow SELECTs, please provide
* SHOW CREATE TABLE tbl\G
* SHOW TABLE STATUS LIKE 'tbl'\G
* EXPLAIN SELECT ...\G
and surround them with [ code ] and [ / code ]