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MDEV-21265: IN predicate conversion to IN subquery should be allowed for a broader set of datatype comparison

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Allow materialization strategy when collations on the
inner and outer sides of an IN subquery are the same and the
character set of the inner side is a proper subset of the character
set on the outer side.
This allows conversion from utf8mb3 to utf8mb4
as the former is a subset of the later.
This is only allowed when IN predicate is converted to an IN subquery

Backported part of the patch (d6a00d9b18) of MDEV-17905.
This commit is contained in:
Varun Gupta
2020-11-27 22:06:54 +05:30
parent f3b10354a9
commit b4379df5b4
9 changed files with 215 additions and 28 deletions
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18
sql/sql_string.h
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@ -131,6 +131,24 @@ uint convert_to_printable(char *to, size_t to_len,
const char *from, size_t from_len,
CHARSET_INFO *from_cs, size_t nbytes= 0);
class Charset
{
CHARSET_INFO *m_charset;
public:
Charset() :m_charset(&my_charset_bin) { }
Charset(CHARSET_INFO *cs) :m_charset(cs) { }
CHARSET_INFO *charset() const { return m_charset; }
/*
Collation name without the character set name.
For example, in case of "latin1_swedish_ci",
this method returns "_swedish_ci".
*/
LEX_CSTRING collation_specific_name() const;
bool encoding_allows_reinterpret_as(CHARSET_INFO *cs) const;
bool eq_collation_specific_names(CHARSET_INFO *cs) const;
};
class String : public Sql_alloc
{
char *Ptr;