• Same answer. Those queries do the same number of reads because they're doing table scans, there's no useful indexes. SQL has to read every single row of every page in that table to evaluate whether or not a row matches those conditions.

    SQL does not do reliable position-based short circuiting. Evaluation order is determined by indexes, data distribution, estimated row counts and the plan that the optimiser comes up with, not the position of the predicate within the where clause. SQL is a declarative language, you specify what you want, not how it must be achieved.

    Hence you may in some cases get short circuiting but it is not guaranteed and a change of data or addition of indexes can change the behaviour entirely. Do not rely on any perceived short circuiting that you see.

    Gail Shaw
    Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
    SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

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