SQL Optimizer Archives - SQLPerformance.com

Some ANY Aggregate Transformations are Broken

Paul White explores two cases where the introduction of the internal ANY aggregate by the optimizer may cause wrong results.

Paul White ◆ July 1, 2019

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SQL Server Join Estimation using Histogram Coarse Alignment

Paul White dives into histograms and explains how the optimizer uses coarse alignment for cardinality estimates.

Paul White ◆ November 20, 2018

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Optimization Thresholds – Grouping and Aggregating Data, Part 5

In the conclusion of his series on grouping and aggregation costs, Itzik Ben-Gan reveals some of the math behind seek vs. scan decisions.

Itzik Ben-Gan ◆ August 8, 2018

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Optimization Thresholds – Grouping and Aggregating Data, Part 4

In the fourth installment of his series on optimization thresholds, Itzik Ben-Gan looks at how SQL Server applies costs to parallel operations.

Itzik Ben-Gan ◆ July 11, 2018

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Optimization Thresholds – Grouping and Aggregating Data, Part 3

Itzik Ben-Gan dissects the Hash Match (Aggregate) algorithm in his latest post in a series on SQL Server optimization thresholds.

Itzik Ben-Gan ◆ June 13, 2018

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Optimization Thresholds – Grouping and Aggregating Data, Part 2

Continuing his series on optimization thresholds, Itzik Ben-Gan dives into the calculations behind stream aggregate costing when the data needs to be sorted first.

Itzik Ben-Gan ◆ May 9, 2018

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Optimization Thresholds – Grouping and Aggregating Data, Part 1

In his first SQLPerformance post, Itzik Ben-Gan shows you how to reverse engineer optimizer costing for a Stream Aggregate operator.

Itzik Ben-Gan ◆ April 10, 2018

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Dealing with date and time instead of datetime

Rob Farley describes a tactic where adding multiple predicates around separate date and time columns can win you some better performance.

Rob Farley ◆ March 29, 2018

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Row Goals, Part 4: The Anti Join Anti Pattern

Paul White continues his series on row goals, treating a redundant and problematic TOP (1) that is added to the inner side of an apply anti join.

Paul White ◆ March 19, 2018

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Row Goals, Part 3: Anti Joins

Continuing his in-depth series on row goals, Paul White explains both why and how they can impact queries involving anti joins.

Paul White ◆ March 7, 2018

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Row Goals, Part 2: Semi Joins

Continuing his series on row goals, Paul White explains how they can impact certain types of semi joins, and how you can spot these effects in showplan and trace flag output.

Paul White ◆ February 22, 2018

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