A discussion on SQL Server
Or “I’m filtering on ISDATE(dt) = 1. Why am I still getting conversion errors?”
Well, to put it simply, because SQL’s evaluating the where clause in a different order to what you may have expected.
Let’s try a simple example.
SELECT * FROM tbl_TestingConversion WHERE ISDate(TheDate)=1 AND CAST(TheDate AS DATETIME) > '2007/07/01'
I was asked a question about this recently, so I thought I’d start this blog off with a brief overview of SQL Server’s execution plans.
Simply put, a query’s execution plan is the query translated into a hierarchical set of operators that the query execution engine understands. The query optimiser is responsible for producing this plan.
A query can have a number of different possible execution plans, depending on the resources available on the server, the amount of data in the source tables, the load on the server.