MDEV-18156 Assertion `0' failed or `btr_validate_index(index, 0, false)' in row_upd_sec_index_entry or error code 126: Index is corrupted upon DELETE with PAD_CHAR_TO_FULL_LENGTH

This change takes into account a column's GENERATED ALWAYS AS
expression dependcy on sql_mode's PAD_CHAR_TO_FULL_LENGTH and
NO_UNSIGNED_SUBTRACTION flags.

Indexed virtual columns as well as persistent generated columns are
now not allowed to have such dependencies to avoid inconsistent data
or index files on sql_mode changes.
So an error is now returned in cases like this:

  CREATE OR REPLACE TABLE t1
  (
    a CHAR(5),
    v VARCHAR(5) AS (a) PERSISTENT -- CHAR->VARCHAR or CHAR->TEXT = ERROR
  );

Functions RPAD() and RTRIM() can now remove dependency on
PAD_CHAR_TO_FULL_LENGTH. So this can be used instead:

  CREATE OR REPLACE TABLE t1
  (
    a CHAR(5),
    v VARCHAR(5) AS (RTRIM(a)) PERSISTENT
  );

Note, unlike CHAR->VARCHAR and CHAR->TEXT this still works,
not RPAD(a) is needed:

  CREATE OR REPLACE TABLE t1
  (
    a CHAR(5),
    v CHAR(5) AS (a) PERSISTENT -- CHAR->CHAR is OK
  );

More sql_mode flags may affect values of generated columns.
They will be addressed separately.

See comments in sql_mode.h for implementation details.

1 files changed, 8 insertions, 0 deletions

diff --git a/sql/sys_vars.cc b/sql/sys_vars.cc
index 04ecbb29b12..8eb75e49d8e 100644
--- a/sql/sys_vars.cc
+++ b/sql/sys_vars.cc
@@ -3160,6 +3160,14 @@ static const char *sql_mode_names[]=
   0
 };
 
+
+const char *sql_mode_string_representation(uint bit_number)
+{
+  DBUG_ASSERT(bit_number < array_elements(sql_mode_names));
+  return sql_mode_names[bit_number];
+}
+
+
 export bool sql_mode_string_representation(THD *thd, sql_mode_t sql_mode,
                                            LEX_STRING *ls)
 {