Bug#15581: COALESCE function truncates mutli-byte TINYTEXT values

field.cc:
  BLOB variations have number-in-bytes limit,
  unlike CHAR/VARCHAR which have number-of-characters limits.
  A tinyblob column can store up to 255 bytes.
  In the case of basic Latin letters (which use 1 byte per character)
  we can store up to 255 characters in a tinyblob column.
  When passing an utf8 tinyblob column as an argument into
  a function (e.g. COALESCE) we need to reserve 3*255 bytes.
  I.e. multiply length in bytes to mbcharlen for the character set.
  Although in reality a tinyblob column can never be 3*255 bytes long,
  we need to set max_length to multiply to make fix_length_and_dec()
  of the function-caller (e.g. COALESCE) calculate the correct max_length
  for the column being created.

ctype_utf8.result, ctype_utf8.test:
  Adding test case.


mysql-test/t/ctype_utf8.test:
  Adding test case.
mysql-test/r/ctype_utf8.result:
  Adding test case.
sql/field.cc:
  Bug#15581: COALESCE function truncates mutli-byte TINYTEXT values
  BLOB variations have byte limits,
  unlike CHAR/VARCHAR which have number-of-character limits.
  It means tinyblob can store up to 255 bytes.
  All of them can be basic latin letters which use 1 byte
  per character.
  I.e. we can store up to 255 characters in a tinyblob column.
  When passing a tinyblob column as an argument into
  a function (for example COALESCE or CONCAT) we
  need to reserve 3*255 bytes in the case of utf-8.
  I.e. multiply length in bytes to mbcharlen for the
  character set.

1 files changed, 3 insertions, 3 deletions

diff --git a/sql/field.cc b/sql/field.cc
index abb5297f458..b1d9167aee2 100644
--- a/sql/field.cc
+++ b/sql/field.cc
@@ -6949,11 +6949,11 @@ uint32 Field_blob::max_length()
   switch (packlength)
   {
   case 1:
-    return 255;
+    return 255 * field_charset->mbmaxlen;
   case 2:
-    return 65535;
+    return 65535 * field_charset->mbmaxlen;
   case 3:
-    return 16777215;
+    return 16777215 * field_charset->mbmaxlen;
   case 4:
     return (uint32) 4294967295U;
   default: