Question

I want to be able to inner join two tables based on the value of a column I’m selecting.

My Query:

SELECT varA, varB, MAX(varC) varC
FROM table1
INNER JOIN table2       ON varB = table2.varB
INNER JOIN @tempTable   ON varA = table1.column
INNER JOIN table3       ON varC = table3.column AND table3.column2 = 1 -- **IF NOT varA = 100**
INNER JOIN table4       ON varC = table4.column  **-- IF varA = 100**
LEFT OUTER JOIN table5  ON table2.column = table5.column AND table5.column2 = 1 AND table5.column3 = 4
GROUP BY varB, varA

So, in short INNER JOIN on table4 if value of column(varA) is not 100 else INNER JOIN on table3

Answer 1

I think this will get the result you’re after:

LEFT JOIN table3       ON varC = table3.column AND table3.column2 = 1 AND varA <> 100 -- **IF NOT varA = 100**
LEFT JOIN table4       ON varC = table4.column  AND varA = 100   **-- IF varA = 100**
...
WHERE (Table3.Column IS NOT NULL OR Table4.Column IS NOT NULL)

Basically allows a join to either table, but only return rows where one of those joins found a record. If you want to return the actual columns from the table as part of the select then you could use an ISNULL:

SELECT ISNULL(Table3.Column, Table4.Column) AS Column

---

EDIT: I should have added that you can’t conditionally join to tables unless you want to use dynamic SQL. You can either join to the table or not. What I outlined above lets you do the join to both tables and then check that one of them did join (which is basically what an Inner Join does).