Question

I use OUTER JOIN to get values stored in rows and show them as columns. When there is no value, I show NULL in column.

Source table:

Id|Name|Value
01|ABCG|,,,,,
01|ZXCB|.....
02|GHJK|;;;;;

View:

Id|ABCG|ZXCB|GHJK
01|,,,,|....|NULL
02|NULL|NULL|;;;;

The query looks like:

SELECT DISTINCT
    b.Id,
    bABCG.Value AS "ABCG"
    bZXCB.Value AS "ZXCB"
    bGHJK.Value AS "GHJK"
FROM
    Bars b
    LEFT JOIN Bars bABCG ON b.Id = bABCG.Id and b.Name = 'ABCG'
    LEFT JOIN Bars bZXCB ON b.Id = bZXCB.Id and b.Name = 'ZXCB'
    LEFT JOIN Bars bGHJK ON b.Id = bGHJK.Id and b.Name = 'GHJK'

I want to remove LEFT JOIN because it’s not allowed in indexed view. I tried replacing it with inner SELECT, but inner SELECT is not allowed also and UNION too. I can’t use INNER JOIN because I want to show NULLs in view. What should I use?

Answer 1

The best you are going to be able to do is use inner joins to get the matches, then union with the left joins and filter it to only return nulls. This probably won’t solve your problem.

I don’t know the specifics of your system but I am assuming that you are dealing with performance issues, which is why you want to use the indexed view. There are a few alternatives, but I think the following is the most appropriate.

Since you commented this is for a DW I am going to assume that your system is more intensive on reads than writes and that data is loaded into it on a schedule by an ETL process. In this kind of high read/low write* situation I would recommend you “materialize” this view, which means when the ETL process runs, to generate the table with your initial select statement that includes the left joins. You will take the hit on the write, then all your reads will be on par with the performance of the indexed view (you would be doing the same thing the indexed view would do, except in a batch instead of on a row by row basis). If your source DB and DW are on the same instance this is a better choice than an indexed view b/c it won’t affect the performance of the source system (indexed views slow down inserts). This is the same concept as the indexed view because you take the performance hit on the insert to speed up the select.

I’ve been down this path before and come to the following conclusion:

An indexed view is more likely to be part of the solution than the entire solution.

*when I said “high read/low write” above you can also think of it as “high read/scheduled write”