Don’t Nest Views

Kevin Feasel

2016-11-29

T-SQL

Denny Cherry recommends against nested views:

Now there are plenty of reasons to use views in applications, however views shouldn’t be the default way of building applications because they do have this potential problems.

While working with a client the other week we had to unwind some massive nest views. Several of these views were nested 5 and 6 levels deep with multiple views being referenced by each view. When queries would run they would take minutes to execute instead of the milliseconds that they should be running in. The problems that needed to be fixed were all indexed based, but because of the massive number of views that needed to be reviewed it took almost a day to tune the single query.

Nested views is usually an indicator of somebody trying to perform OOP on a relational database, taking advantage of encapsulation.  One big performance problem with nested views is that at some point, the query optimizer gives up trying to optimize and simply pulls in all of the tables as many times as they appear.  Make the optimizer’s life easier and it will make your life easier.

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