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Normalise associative operations

Applies to ✅ Open Source Edition   ✅ Express Edition   ✅ Professional Edition   ✅ Enterprise Edition

Associative operations are operations whose chaining can be done as (a op b) op c or a op (b op c) without changing the result. Examples of such operations are:

  • +
  • *
  • AND
  • OR

In order to simplify all of these pattern replacements, we normalise associative ops to always flatten tree structures into lists.

Using Settings.transformPatternsNormaliseAssociativeOps, the following transformations can be achieved:

-- With Settings.transformPatternsNormaliseAssociativeOps active, this:
  (a + b) + (c + d),
  (a * b) * (c * d),
  (a AND b) AND (c AND d),
  (a OR b) OR (c OR d)
FROM tab;

-- ... is transformed into the equivalent expression:
  ((a + b) + c) + d,       -- (a + b) + (c + d)
  ((a + b) + c) + d,       -- (a * b) * (c * d)
  ((a AND b) AND c) AND d, -- (a AND b) AND (c AND d)
  ((a OR b) OR c) OR d     -- (a OR b) OR (c OR d)
FROM tab;

Note that the unnecesary parentheses may not be generated in either case, but the in-memory data structure still looks as though the parentheses were there.


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