Question

I have a question about JOINS.
Does Sql JOINs reduce performance in a query?
I have query with many JOIN in it . Can I say that the bad performance is come from these JOINS? if yes ,what should I do instead of JOIN in a query?

here is a piece of my query

......
FROM (((((tb_Pinnummern INNER JOIN tb_Fahrzeug ON tb_Pinnummern.SG = tb_Fahrzeug.Motor_SG) INNER JOIN tb_bauteile ON tb_Pinnummern.Bauteil = tb_bauteile.ID) LEFT JOIN Fehlercodes_akt_Liste AS Fehlercodes_akt_Liste_FC_Plus ON Fehlercodes_akt_Liste_FC_Plus.ID=tb_bauteile.[FC_Plus]) LEFT JOIN Fehlercodes_akt_Liste AS Fehlercodes_akt_Liste_FC_Minus ON Fehlercodes_akt_Liste_FC_Minus.ID=tb_bauteile.[FC_Minus]) LEFT JOIN Fehlercodes_akt_Liste AS Fehlercodes_akt_Liste_FC_Unterbrechung ON Fehlercodes_akt_Liste_FC_Unterbrechung.ID=tb_bauteile.[FC_Unterbrechung]) LEFT JOIN Fehlercodes_akt_Liste AS Fehlercodes_akt_Liste_FC_Aderschl ON Fehlercodes_akt_Liste_FC_Aderschl.ID=tb_bauteile.[FC_Aderschl]
WHERE (((tb_Fahrzeug.ID)=[forms]![frm_fahrzeug]![id]));

Answer 1

Well joins obviously need to be processed and this processing will consume cpu, memory and IO.

As well as this we have to consider that joins can perform really, really badly if the right indexes etc are not in place.

However, an SQL join with the correct supporting indexes will produce the result you require faster than any other method.

Just consider what you would need to do to calculate the same result as your SQL above. Read the first table, then sort into the correct order, then read the second table and sort it then merge the two result sets before proceeding to the third table ……
Or read all the rows from the first table and for each row issue SQL to retrieve the matching rows.