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, 5 insertions, 0 deletions

diff --git a/sql/item_func.h b/sql/item_func.h
index 81a7e948085..5be62427852 100644
--- a/sql/item_func.h
+++ b/sql/item_func.h
@@ -773,11 +773,16 @@ public:
 
 class Item_func_minus :public Item_func_additive_op
 {
+  Sql_mode_dependency m_sql_mode_dependency;
 public:
   Item_func_minus(THD *thd, Item *a, Item *b):
     Item_func_additive_op(thd, a, b) {}
   const char *func_name() const { return "-"; }
   enum precedence precedence() const { return ADD_PRECEDENCE; }
+  Sql_mode_dependency value_depends_on_sql_mode() const
+  {
+    return m_sql_mode_dependency;
+  }
   longlong int_op();
   double real_op();
   my_decimal *decimal_op(my_decimal *);