mysql - Conditional Where clause in sql -

select cola, colb car car.id in (select id make) ,  car.id in (select id model); 

the above query works file is, there case make table has not been popluated anything. empty table. there way make join not take place on table?

basically, if table has 1 or more rows, apply condition. otherwise, ignore , dont limit it.

is there way achieve same result on left join?

edit

result algorithm:

• select stuff original table car.
• take away not in table make if make has content
• take away not in table model if model has content....
• take away in table model2 if model2 has content....

thisnk of model2 table of things dont want, , model , make tables of things want.

select cola, colb car ((select count(*) make) = 0) or id in (select id make))   , id in (select id model) 

with left join:

select distinct cola, colb car join (select count(*) c make) mcount left join make on car.id = make.id join model on car.id = model.id mcount.c = 0 or make.id not null 

using or can prevent use of indexes, may better use union:

select distinct cola, colb car join make on car.id = make.id join model on car.id = model.id  union  select distinct cola, colb car join (select count(*) c make) make join model on car.id = model.id make.c = 0 

extending left join version both tables straightforward:

select distinct cola, colb car join (select count(*) c make) makecount left join make on car.id = make.id join (select count(*) c model) modelcount left join model on car.id = model.id (makecount.c = 0 or make.id not null)   , (modelcount.c = 0 or model.id not null) 

if there other tables join with, can keep repeating pattern.

doing union query harder, because need subquery each combination of join tables can empty: 1 subquery both make , model having rows, 1 make, 1 model, , 1 both being empty. if there 3 tables being joined with, expand 8 subqueries (i.e. there 2ⁿ subqueries). maybe can come way better, can't think of off top of head.