in the SQL parser.

Various backslash escapes and quote-quote escaped sequences are covered
in combination with single and multi-byte characters.

This is especially important for the character sets that can have 0x5C
as the second byte in a multi-byte character (big5, cp932, gbk, sjis).

swe7 is also a special character set, because in swe7 0x5C is used for
both escape character and for "LATIN CAPITAL LETTER O WITH DIAERESIS".