SQL Query Help

[willichan]

Hopefully someone a little more solid in SQL can give me a hand.

I have a many-to-many-to-many setup.

a.field1
a.field2
a.field3

x.afield1
x.bfield1

b.field1
b.field2
b.field3

y.bfield1
y.cfield1

c.field1
c.field2
c.field3

In essence, I need all a.field1 where c.field3="stringvalue".

I could do it with multiple queries, and looping, but I am hoping there is a simpler, single query I can make.

Thanks in advance for any help.

Edited April 5, 2016 by willichan
clarity

[jchd]

Are you looking for a join or rather reorganizing your schema to use foreign keys?

Your question doesn't make any sense to me as it is. Are a, b, c, x, y tables? What are the relationships you want to modelize?

[willichan]

Sorry.  I should have explained the tables better.

A, B, and C are the tables containing the data.

X and Y are the tables that contain the many-to-many links between the data tables.

I need to identify any A that are linked by X to any B that are linked by Y to any C that hold a particular value.

Yes, I believe this would need to be done with joins.  SQL is unfortunately a weak area for me, especially where joins are concerned.  I definitely need to study up on the subject.

---

I just noticed the other point of confusion I created.  I will fix the schema in the first post.

Edited April 5, 2016 by willichan

[Bowmore]

You did not mention which database you are using, but the following should give you the required result on most databases that follow the latest ANSI SQL standard.

 

SELECT a.field1, c.field3 
  FROM a 
       JOIN x ON (a.field1  = x.afield1) 
       JOIN b ON (x.bfield1 = b.field1)                        
       JOIN y ON (b.field1  = y.bfield1)                        
       JOIN c ON (y.cfield1 = c.field1)
 WHERE c.field3 = 'stringvalue'

 

[jchd]

As Bowmore showed this can be achieved thru a simple join, yet I'd recommend you normalize your schema by using foreign keys. The query would be essentially the same but linking fields would now be made by row IDs, almost always 64-bit integers.

[willichan]

Thank you both.

@Bowmore,

That will be far simpler than what I was trying to concoct.

@jchd,

I agree, unfortunately, I don't have control over the database.  I am building a migration tool from some old, screwball system developed by an overseas affiliate company to a new system we are implementing.

At some point, I should hit you up for recommendations to read up on SQL syntax.  I seem to be getting more tasks that need it lately.

 

Thanks again to both of you.

[jchd]

Ask anytime. Good luck in the meantime.