These directives did not have any affect.

All these affected lines:

1.  | INTERVAL_SYM expr interval '+' expr

2.  | INTERVAL_SYM '(' expr ',' expr ')'

3.  | INTERVAL_SYM '(' expr ',' expr ',' expr_list ')'

4.  | DATE_ADD_INTERVAL '(' expr ',' INTERVAL_SYM expr interval ')'

5.  | DATE_SUB_INTERVAL '(' expr ',' INTERVAL_SYM expr interval ')'

define the grammar unambiguously.

"bison -v sql_yacc.yy" produces exactly the same sql_yacc.output
before and after the change.