MySQL  8.0.27
Source Code Documentation
sql_const_folding.h
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1 #ifndef SQL_CONST_FOLDING_INCLUDED
2 #define SQL_CONST_FOLDING_INCLUDED
3 
4 /* Copyright (c) 2018, 2021, Oracle and/or its affiliates.
5 
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25 
26 /**
27  @file sql/sql_const_folding.h
28 
29  Interface to SQL expression constant folding
30 */
31 
32 #include "sql/item.h" // Item, Item::cond_result
33 class THD;
34 
35 /**
36  Fold boolean condition {=, <>, >, >=, <, <=, <=>} involving constants and
37  fields (or references to fields), possibly determining if the condition is
38  always true or false based on type range of the field, or possibly simplifying
39  >=, <= to = if constant lies on the range border.
40 
41  Also fold such conditions if they are present as arguments of other functions
42  in the same way, except there we replace the arguments with manifest FALSE or
43  field <> field to exclude NULLs if the field is nullable, cf.
44  ignore_unknown().
45 
46  The constants are always converted to constants of the type of the field, no
47  widening of the field type in therefore necessary after this folding for
48  comparison to occur. When converting constants to decimal (when the field is a
49  decimal), the constant will receive the same number of fractional decimals as
50  the field. If decimal constant fraction truncation occurs, the comparison
51  {GT,GE,LT,LE} logic is adjusted to preserve semantics without widening the
52  field's type.
53 
54  @param thd session state
55  @param cond the condition to handle
56  @param[out] retcond condition after const removal
57  @param[out] cond_value resulting value of the condition
58  - COND_OK: condition must be evaluated (e.g int == 3)
59  - COND_TRUE: always true (e.g signed tinyint < 128)
60  - COND_FALSE: always false (e.g unsigned tinyint < 0)
61 
62  @param manifest_result
63  For IS NOT NULL on a not nullable item, if true,
64  return item TRUE (1), else remove condition and return
65  COND_TRUE. For cmp items, this is determined by
66  Item_bool_func2::ignore_unknown.
67  @returns false if success, true if error
68 */
69 bool fold_condition(THD *thd, Item *cond, Item **retcond,
70  Item::cond_result *cond_value,
71  bool manifest_result = false);
72 
73 #endif /* SQL_CONST_FOLDING_INCLUDED */
Base class that is used to represent any kind of expression in a relational query.
Definition: item.h:802
cond_result
Definition: item.h:871
For each client connection we create a separate thread with THD serving as a thread/connection descri...
Definition: sql_class.h:821
bool fold_condition(THD *thd, Item *cond, Item **retcond, Item::cond_result *cond_value, bool manifest_result=false)
Fold boolean condition {=, <>, >, >=, <, <=, <=>} involving constants and fields (or references to fi...
Definition: sql_const_folding.cc:1253