Conditionally Join the Table with a Condition - sql

Question

I have 3 tables. BaseProducts, Products and ProductsMerchants. I need to find the count using a condition. This is my SQL,
ALTER PROCEDURE [dbo].[GetTotalProductsCount]
(
#SuperUser bit,
#MarchantId int
)
AS
BEGIN
IF(#SuperUser = 1)
BEGIN
SELECT COUNT(*) AS Total
FROM [dbo].[BaseProducts]
END
ELSE
BEGIN
SELECT COUNT(*) AS Total
FROM [dbo].[BaseProducts] BP
INNER JOIN [dbo].[Products] P ON P.BaseProductId = BP.Id
INNER JOIN ProductsMerchants PM ON PM.ProductId = P.Id
WHERE PM.MarchantId = #MarchantId;
END
END
The problem is that I need to rewrite the same query just for checking a condition. Can I make it one query?

Answer 1

You can do this:
SELECT COUNT(*) AS Total
FROM [dbo].[BaseProducts]
WHERE #SuperUser = 1
UNION ALL
SELECT COUNT(*) AS Total
FROM [dbo].[BaseProducts] BP
INNER JOIN [dbo].[Products] P ON P.BaseProductId = BP.Id
INNER JOIN ProductsMerchants PM ON PM.ProductId = P.Id
WHERE PM.MarchantId = #MarchantId AND #SuperUser <> 1;
Personally, I find the if form more understandable.
If the inner joins are being used for filtering and don't increase the number of rows, you could also do:
SELECT COUNT(*) AS Total
FROM [dbo].[BaseProducts] BP
LEFT JOIN [dbo].[Products] P ON P.BaseProductId = BP.Id
LEFT JOIN ProductsMerchants PM ON PM.ProductId = P.Id
WHERE PM.MarchantId = #MarchantId OR #SuperUser = 1;
(The PM.MarchantId = #MarchantId undoes the left outer join.)
But once again, I find that the intent of the if is clearer.
Or even this:
SELECT (CASE WHEN #SuperUser = 1 THEN CNT ELSE COUNT(*) END) AS Total
FROM (SELECT COUNT(*) as CNT FROM [dbo].[BaseProducts] BP) const CROSS JOIN
[dbo].[BaseProducts] BP
INNER JOIN [dbo].[Products] P ON P.BaseProductId = BP.Id
INNER JOIN ProductsMerchants PM ON PM.ProductId = P.Id
WHERE PM.MarchantId = #MarchantId OR #SuperUser = 1;