Question

Here is my scenario

Table 1: GID || Info1

Table 2: GID || Tb1GID (refers
to GID of Table1) || Info2

Table 3: GID || Info3

Table 4: GID || Tb2GID (refers to
GID of Table2 || Tb3GID (refers to
Table3 GID || Value

Now I have to build an sql query to get the value, given a particular Info1, Info2, Info3.
Essentially, I have to get the GID, of table 1 using info1, GID of table to , by mapping info2 and GID of table 1. And then get the GID of table 3 using info 3. And combine these to GIDs to get the value in table 4.

What is the most optimal way of constructing an sql query for this one?

Answer 1

Just join the tables on the id:s and match the info values in the condition:

select
  t4.Value
from
  [Table 1] as t1
  inner join [Table 2] as t2 on t2.Tb1GID = t1.GID
  inner join [Table 4] as t4 on t4.Tb2GID = t2.GID
  inner join [Table 3] as t3 on t3.GID = t4.Tb3GID
where
  t1.Info1 = @Info1 and
  t2.Info2 = @Info2 and
  t3.Info3 = @Info3

This communicates most clearly how the relations work, giving the query planner the best information to work with.