如何在JOIN子句中为所有表测试相同的列值？

Question

I have the following example query;

SELECT S.Column1, S.Column2
FROM TableS as S
LEFT JOIN TableP as P ON S.PID = P.ID
LEFT JOIN TableI as I ON P.IID = I.ID
WHERE I.Identifier = 'StringIdentifier'
      AND I.Relevant = 1
      AND P.Relevant = 1
      AND S.Relevant = 1 

Is there any way to simplify the last 3 lines to only one, to check the Relevant column from all the tables in one go?

Obviously replacing the last 3 lines with just a line AND Relevant = 1 will not work because it gives the error:

Ambiguous column name 'Relevant'.

Edit: The datatype of Relevant column is bit.

Answer 1

If you have an index on that column, then this is the way to go.

If you do not, and just want it to look fancy or nice you can do something like:

AND I.Relevant * P.Relevant * S.Relevant = 1 -- assuming they are numeric
AND I.Relevant & P.Relevant & S.Relevant = 1 -- assuming bit

If not numeric or bit (text) then you need to cast to numeric and it will again not look that nice.

Also, I would suggest losing the left (from join) as in many cases it will be faster and on this code it does not make sense.

Answer 2

Your WHERE condition are turning the JOIN s into inner joins, so you should express the joins correctly:

SELECT S.Column1, S.Column2
FROM TableS S JOIN
     TableP P
     ON S.PID = P.ID JOIN
     TableI I
     ON P.IID = I.ID AND I.Identifier = 'StringIdentifier'
WHERE I.Relevant = 1 AND
      P.Relevant = 1 AND
      S.Relevant = 1;

Assuming Relevant takes on only the values of 0/1, you could use a lateral join:

SELECT S.Column1, S.Column2
FROM TableS S JOIN
     TableP P
     ON S.PID = P.ID JOIN
     TableI I
     ON P.IID = I.ID AND
        I.Identifier = 'StringIdentifier' CROSS APPLY
     (SELECT MIN(v.Relevant) as min_relevant
      FROM (VALUES (I.Relevant), (P.Relevant), (S.Relevant)
           ) v(Relevant)
     ) v
WHERE v.min_relevant = 1;

This isn't really helpful for 3 comparisons. But if you had a dozen, it would be useful.

Answer 3

If your problem is that you have to repeat the 1 and not the length of the expression you could use ALL .

SELECT S.Column1, S.Column2
FROM TableS as S
LEFT JOIN TableP as P ON S.PID = P.ID
LEFT JOIN TableI as I ON P.IID = I.ID
WHERE I.Identifier = 'StringIdentifier'
      AND 1 = ALL(SELECT I.Relevant
                  UNION
                  SELECT P.Relevant
                  UNION
                  SELECT S.Relevant)

Answer 4

That query is wrong because there are 2 left join but in the where there are conditions over those tables I propose:

SELECT S.Column1, S.Column2
FROM TableS as S
    LEFT JOIN TableP as P ON S.PID = P.ID AND P.Relevant = 1
    LEFT JOIN TableI as I ON P.IID = I.ID AND I.Identifier = 'StringIdentifier' AND I.Relevant = 1
WHERE S.Relevant = 1 

It is better a correct query than a simplified query

Answer 5

假设相关是个笨蛋，您可以做

... and I.Relevant and P.Relevant and S.Relevant