sql order by - MYSQL has orderBy on count(*) some impact on perfomance? -

i have simple query count number of records plain query inner joins , criterions.

something this.

select count(*) ...... .... order .........at 4 fields. 

my question order asc or desc @ 4 fields has impact on performance? or ignore or optimized engine.

sorry if question plain or simple best regards.

first, should note query, written, return 1 row. have aggregation function no group by. in situation, order by no-op (i don't know if mysql goes through motions 1 row or not).

in general, performance impact of order by depends on number of rows, not number of keys.

i can think of 2 occasions when order by has minimal impact on performance:

• an index can used ordering.
• it follows group by , uses aggregation keys (this true in mysql sort group by).

and, of course, order by on few rows (such 4 rows) pretty negligible performance-wise.

the impact, though, has less size of keys number of rows , overall size of rows. multiple joins , where clause, unlikely (but not impossible) query use index order by.