mysql - Inner Joins over Multiple Tables -


i think, have misconception, how join works on multiple tables. lets have 3 tables a, b, c , need join them.

here v1

select a.name name1     ,b.name name2     ,c.name name3 inner join b     on a.id = b.id inner join c     on b.id = c.id

here v2

select a.name name1     ,d.name name2     ,d.name name3 inner join (     select b.name name2         ,c.name name3     b     inner join c         on b.id = c.id     ) d     on a.id = d.id

is there performance difference between 2 versions? though first query looks cleaner, need build query builder ui, restricting joins 2 tables helps.

in general, problem subselects can require rdbms create temporary table fulfill subselect - , on large enough table can serious expense - , potentially can't use indexes on subselect optimize query, , you're scanning table.

of course, ddl , size of tables aren't included, best way have postgres explain plans , compare/contrast.


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