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  • Closest Match with Sort Rewinds

    In When Do SQL Server Sorts Rewind? I described how most sorts can only rewind when they contain at most one row. The exception is in-memory sorts, which can rewind at most 500 rows and 16KB of data. These are certainly tight restrictions, but we can still make use of them on occasion. To illustrate, I am going reuse a demo Itzik Ben-Gan ...
    Posted to Page Free Space (Weblog) by Paul White on October 18, 2020
  • SQL Server 2019 Aggregate Splitting

    The SQL Server 2019 query optimizer has a new trick available to improve the performance of large aggregations. The new exploration abilities are encoded in two new closely-related optimizer rules: GbAggSplitToRanges SelOnGbAggSplitToRanges The extended event query_optimizer_batch_mode_agg_split is provided to track when this new ...
    Posted to Page Free Space (Weblog) by Paul White on August 3, 2020
  • A bug with Halloween Protection and the OUTPUT Clause

    Background The OUTPUT clause can be used to return results from an INSERT, UPDATE, DELETE, or MERGE statement. The data can be returned to the client, inserted to a table, or both. There are two ways to add OUTPUT data to a table: Using OUTPUT INTO With an outer INSERT statement. For example: -- Test table DECLARE @Target ...
    Posted to Page Free Space (Weblog) by Paul White on August 3, 2020
  • Pulling Group By Above a Join

    One of the transformations available to the SQL Server query optimizer is pulling a logical Group By (and any associated aggregates) above a Join. Visually, this means transforming a tree of logical operations from: …to this: The above diagrams are logical representations. They need to be implemented as physical operators to appear in an ...
    Posted to Page Free Space (Weblog) by Paul White on August 3, 2020
  • Did You Know? Everything's Up to Date in Kansas City!

    They are so up-to-date, I have chosen it as one of the handful of  cities on my user group tour... I'll be presenting a full day seminar on Controlling and Reusing Query Plans in SQL Server 2005. You can get more information from  my schedule page at schedule.KalenDelaney.com Full details, including registration information, can be ...
    Posted to Kalen Delaney (Weblog) by Kalen Delaney on February 1, 2008
  • Did you know? Cloning is Legal (and Available in SQL Server 2005)

      I first heard about the possibility of database cloning way back in version 7.0 and thought it sounded like a great idea. Who wouldn't love to have a bunch of identical little databases running around, of smaller size and easier manageability? Cloning a database means creating a statistics only copy of it, so that you can examine ...
    Posted to Kalen Delaney (Weblog) by Kalen Delaney on November 21, 2007
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