Забыл указать то что может быть в поле categoryid - неизвестно. Там может быть любая цифра.

49487707

Starting 8 µs
Waiting For Query Cache Lock 2 µs
Checking Query Cache For Query 23 µs
Checking Permissions 3 µs
Opening Tables 21 µs
System Lock 5 µs
Waiting For Query Cache Lock 16 µs
Init 9 µs
Optimizing 4 µs
Statistics 8 µs
Preparing 6 µs
Executing 2 µs
Sending Data 31.9 ms
End 10 µs
Query End 3 µs
Closing Tables 8 µs
Freeing Items 4 µs
Waiting For Query Cache Lock 1 µs
Freeing Items 162 µs
Waiting For Query Cache Lock 2 µs
Freeing Items 1 µs
Storing Result In Query Cache 2 µs
Logging Slow Query 1 µs
Cleaning Up 1 µs

Starting 9 µs
Waiting For Query Cache Lock 2 µs
Checking Query Cache For Query 23 µs
Checking Permissions 4 µs
Opening Tables 13 µs
System Lock 6 µs
Waiting For Query Cache Lock 10 µs
Init 9 µs
Optimizing 4 µs
Executing 5 µs
End 2 µs
Query End 1 µs
Closing Tables 5 µs
Freeing Items 2 µs
Waiting For Query Cache Lock 1 µs
Freeing Items 43 µs
Waiting For Query Cache Lock 2 µs
Freeing Items 1 µs
Storing Result In Query Cache 2 µs
Logging Slow Query 1 µs
Cleaning Up 3 µs

P.S. GoDr select count(*) быстрее, чем select count(`id`)

COUNT(*) is optimized to return very quickly if the SELECT retrieves from one table, no other columns are retrieved, and there is no WHERE clause. For example:
mysql> SELECT COUNT(*) FROM student;
This optimization applies only to MyISAM and ISAM tables only, because an exact record count is stored for these table types and can be accessed very quickly. For transactional storage engines (InnoDB, BDB), storing an exact row count is more problematic because multiple transactions may be occurring, each of which may affect the count.