Building Your T-SQL Tool Kit: Logical Query Processing
“Column dbo.xyz' is invalid in the select list because it is not contained in either an aggregate function
or the GROUP BY clause.” Seen it; fixed it, but can we explain why we’re getting a syntax in the first
place? The optimizer must follow a very specific hierarchy in order to generate a plan. When you
understand the hierarchy, then you better understand the behavior of the optimizer.
This all-demo session will explain the logical processing hierarchy, giving you the foundation
knowledge you need to build well-structured queries that keep the optimizer happy. Learn how the
FROM clause is processed, why a calculated column’s alias can’t be addressed in the JOIN, why WHERE
isn’t the only filter, and why NULL confuses everything. When you leave, you will think very differently
about how you build your queries, and the query optimizer will love you for learning to speak its
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Christina Leo is a Netherlands based, independent consultant specializing in T-SQL development and performance tuning. She happily shares her 14 years of technical experience with the SQL Server community by teaching at local and international SQL Server user group meetings and technical events, including multiple SQL Saturdays, SQL Bits, TechEd Africa, and the PASS Summit.
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