Wednesday, 14 November 2018

How can I join multiple SQL tables using the IDs?

I have 4 different tables that I want to join. The tables are structured with columns as follows:
TableA - aID | nameA | dID

TableB - bID | nameB | cID | aID

TableC - cID | nameC | date

TableD - dID | nameD
Starting with Table A, I understand how to JOIN tables a and c using b, since b has the
 Primary Keys for those tables. I want to be able to join table TableD on TableA as well. 
Below is my SQL statement that first joins tables A and B, then joins that to C:
SELECT TableA.*, TableB.*, TableC.* FROM (TableB INNER JOIN TableA
ON TableB.aID= TableA.aID)
INNER JOIN TableC ON(TableB.cID= Tablec.cID)
WHERE (DATE(TableC.date)=date(now())) 
When I attempt to add another join, to include D, I get an error that 'TableD' is unknown:
 SELECT TableA.*, TableB.*, TableC.*, TableD.* FROM (TableB INNER JOIN TableA
    ON TableB.aID= TableA.aID)
    INNER JOIN TableC ON(TableB.cID= Tablec.cID)
    INNER JOIN TableA ta ON(ta.dID= TableD.dID)
    WHERE (DATE(TableC.date)=date(now())) 

 Answers


You want something more like this:
SELECT TableA.*, TableB.*, TableC.*, TableD.*
FROM TableA
    JOIN TableB
        ON TableB.aID = TableA.aID
    JOIN TableC
        ON TableC.cID = TableB.cID
    JOIN TableD
        ON TableD.dID = TableA.dID
WHERE DATE(TableC.date)=date(now()) 
In your example, you are not actually including TableD. All you have to do is perform 
another join just like you have done before.
A note: you will notice that I removed many of your parentheses, as they really are not 
necessary in most of the cases you had them, and only add confusion when trying to read 
the code. Proper nesting is the best way to make your code readable and separated out.



You have not joined TABLED merely selected the FIELD TABLED from one of the tables.

0 comments:

Post a Comment