May 2019
Intermediate to advanced
484 pages
11h 23m
English
Content preview from Learn T-SQL Querying
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Pitfalls of correlated sub-queries
It is not uncommon to use sub-queries to express certain predicates inline in queries, but developers must keep in mind that joins are frequently better than correlated sub-queries.
The following query examples can be executed in the scope of the AdventureWorks sample database:
SELECT wo.StockedQty, wo.WorkOrderID, wor.ActualCostFROM Production.WorkOrder AS woINNER JOIN Production.WorkOrderRouting AS wor ON wo.WorkOrderID = wor.WorkOrderIDWHERE wor.WorkOrderID = 12345;SELECT wo.StockedQty, wo.WorkOrderID, (SELECT wor.ActualCost FROM Production.WorkOrderRouting AS wor WHERE wor.WorkOrderID = 12345)FROM Production.WorkOrder AS woWHERE wo.WorkOrderID IN (SELECT wor.WorkOrderID FROM Production.WorkOrderRouting ...
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