Understanding where QTA is needed

We discussed how the CE version is tied to the concept of database compatibility level in the Introducing the Cardinality Estimator section of Chapter 3, Mechanics of the Query Optimizer. The CE version that our databases use influences how query plans are calculated for queries that will execute in those databases. And we have seen first-hand the effects of the CE every time we compared the estimated number of rows with the actual number of rows throughout the book—for example in the Query plan comparison section of Chapter 10, Comparative Analysis of Query Plans, where we dealt with the row goal optimization.

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