如何从联接查询中获取一列的DISINCT值

Question

I am having a query like

SELECT DISTINCT table_1.id_1,
    table_1.id_2,
    table_1_id_3
FROM table_1
INNER JOIN table_2
    ON table_1.id_1 = table_2.id_1
        AND table_1.id_2 = table_2.id_2
INNER JOIN table_3
    ON table_2.id_1 = table_3.id_2
        AND table_2.id_2 = table_3.id_2
WHERE table_2.code = 'Y'
    AND table_2.site = 'N'
    AND table_3.code = 'Q'

This gives me distinct combination of id_1, id_2 and id_3 satisfying the conditions. How should the query be to get distinct values of only id_1 matching all the conditions.

I am not posting the table contents as they are having large number of columns and as this question is a query specific one.

Answer 1

You could remove the second and third fields from the query.

SELECT DISTINCT 
    table_1.id_1    
FROM table_1
INNER JOIN table_2
    ON table_1.id_1 = table_2.id_1
        AND table_1.id_2 = table_2.id_2
INNER JOIN table_3
    ON table_2.id_1 = table_3.id_2
        AND table_2.id_2 = table_3.id_2
WHERE table_2.code = 'Y'
    AND table_2.site = 'N'
    AND table_3.code = 'Q'