The patch for "MDEV-25440: Indexed CHAR ... broken with NO_PAD collations"
fixed these scenarios from MDEV-26743:
- Basic latin letter vs equal accented letter
- Two letters vs equal (but space padded) expansion
However, this scenario was still broken:
- Basic latin letter (but followed by an ignorable character)
vs equal accented letter
Fix:
When processing for a NOPAD collation a string with trailing ignorable
characters, like:
'<non-ignorable><ignorable><ignorable>'
the string gets virtually converted to:
'<non-ignorable><ignorable><ignorable><space><space><space>...'
After the fix the code works differently in these two cases:
1. <space> fits into the "nchars" limit
2. <space> does not fit into the "nchars" limit
Details:
1. If "nchars" is large enough (4+ in this example),
return weights as follows:
'[weight-for-non-ignorable, 1 char] [weight-for-space-character, 3 chars]'
i.e. the weight for the virtual trailing space character now indicates
that it corresponds to total 3 characters:
- two ignorable characters
- one virtual trailing space character
2. If "nchars" is small (3), then the virtual trailing space character
does not fit into the "nchar" limit, so return 0x00 as weight, e.g.:
'[weight-for-non-ignorable, 1 char] [0x00, 2 chars]'
Adding corresponding MTR tests and unit tests.
cmp_data(): Compare different-length CHAR fields with
the new strnncollsp_nchars function that will pad spaces if needed.
Any InnoDB ROW_FORMAT except the original one that was named
ROW_FORMAT=REDUNDANT in MySQL 5.0.3 will internally store
CHAR(n) columns as variable-length if the character encoding is
variable length. Spaces may be trimmed from the end.
For NOT NULL values, the minimum length is always n*mbminlen.
In cmp_data() we only know the lengths in bytes and we cannot
easily know the ROW_FORMAT.
is_strnncoll_compatible(): Refactored from innobase_mysql_cmp().
innobase_mysql_cmp(): Merged to cmp_whole_field().
cmp_whole_field(): Invoke strnncollsp_nchars for the DATA_MYSQL
(the CHAR type with any other collation than latin1_swedish_ci).
Reviewed by: Alexander Barkov
Tested by: Roel Roel Van de Paar
