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  1. MariaDB Server
  2. MDEV-23860

Move all optimization query re-writes from the prepare phase into the optimizer phase

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    Description

      Currently the function check_and_do_in_subquery_rewrite() is called at the prepare phase. Here's what the function does:

        /*
      		 
          If
      		 
            1) this join is inside a subquery (of any type except FROM-clause
      		 
               subquery) and
      		 
            2) we aren't just normalizing a VIEW
      		 
       
      		 
          Then perform early unconditional subquery transformations:
      		 
           - Convert subquery predicate into semi-join, or
      		 
           - Mark the subquery for execution using materialization, or
      		 
           - Perform IN->EXISTS transformation, or
      		 
           - Perform more/less ALL/ANY -> MIN/MAX rewriter
      		 
           - Substitute trivial scalar-context subquery with its value
      		 
       
      		 
      */

      All the the rewrites above are actually an optimization re-writes. Most of them transform the query tree into a form that cannot be converted into a proper equivalent SQL query. This prevents usage of an external SQL parser after the prepare stage if any of such transformation has been performed.
      From architectural point of view doing such re-writes in the middle of the prepare stage is also not a proper solution because some of the transformation may be rejected at the optimization stage.

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          duplicates

          Task - A task that needs to be done. MDEV-23450 Move subquery rewrites from JOIN::prepare into JOIN::optimize

          • Major - Major loss of function.
          • Open
          relates to

          New Feature - A new feature of the product, which has yet to be developed. MDEV-22366 Changes in optimizer to allow better operation of Smart Engine

          • Major - Major loss of function.
          • Open

          Task - A task that needs to be done. MDEV-23791 Segregate some of optimizer rewrites into separate functions

          • Major - Major loss of function.
          • Closed

          Task - A task that needs to be done. MDEV-23792 Add methods to disable some of optimizations/rewrites

          • Major - Major loss of function.
          • Open

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              serg Sergei Golubchik
              igor Igor Babaev
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              Dates

                Created:
                Updated:
                Resolved:

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