MySQL 8.0.29
Source Code Documentation
common_subexpression_elimination.h
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22
23#ifndef SQL_JOIN_OPTIMIZER_COMMON_SUBEXPRESSION_ELIMINATION
24#define SQL_JOIN_OPTIMIZER_COMMON_SUBEXPRESSION_ELIMINATION 1
25
26class Item;
27
28/**
29 Do simple CSE (common subexpression elimination) on “item”, and return
30 the answer. The CSE done is exclusively moving common expressions out
31 of conjunctions-of-disjunctions, ie. it rewrites
32
33 (a AND b) OR (a AND c)
34
35 into
36
37 a AND (b OR c)
38
39 The primary motivation is that such split-out items are more versatile;
40 they can be pushed independently, be made into hash join conditions etc.
41 However, an added bonus is that the expressions will simply execute faster.
42
43 This function does not descend into subexpressions that are not AND/OR
44 conjunctions, so e.g. an expression like
45
46 1 + ((a AND b) OR (a AND c))
47
48 will be left as-is.
49 */
51
52#endif // SQL_JOIN_OPTIMIZER_COMMON_SUBEXPRESSION_ELIMINATION
Base class that is used to represent any kind of expression in a relational query.
Definition: item.h:802
Item * CommonSubexpressionElimination(Item *cond)
Do simple CSE (common subexpression elimination) on “item”, and return the answer.
Definition: common_subexpression_elimination.cc:183