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, 2 insertions, 0 deletions

diff --git a/sql/item_cmpfunc.h b/sql/item_cmpfunc.h
index 5045e39fc5a..0a5abfe6273 100644
--- a/sql/item_cmpfunc.h
+++ b/sql/item_cmpfunc.h
@@ -489,6 +489,7 @@ public:
   {
     allowed_arg_cols= 0;  // Fetch this value from first argument
   }
+  Sql_mode_dependency value_depends_on_sql_mode() const;
   void print(String *str, enum_query_type query_type)
   {
     Item_func::print_op(str, query_type);
@@ -1920,6 +1921,7 @@ public:
     Item_bool_func2(thd, a, b), canDoTurboBM(FALSE), pattern(0), pattern_len(0),
     bmGs(0), bmBc(0), escape_item(escape_arg),
     escape_used_in_parsing(escape_used), use_sampling(0), negated(0) {}
+  Sql_mode_dependency value_depends_on_sql_mode() const;
   longlong val_int();
   enum Functype functype() const { return LIKE_FUNC; }
   void print(String *str, enum_query_type query_type);