Item_func_tochar::check_arguments() didn't check if its arguments
each had one column. Failing to make this check and proceeding would
eventually cause either an assertion failure or the execution would
reach "MY_ASSERT_UNREACHABLE();" which would produce a crash with
a misleading stack trace.
* Fixed Item_func_tochar::check_arguments() to do the required check.
* Also fixed MY_ASSERT_UNREACHABLE() to terminate the program. Just
"executing" __builtin_unreachable() used to cause "undefined results",
which in my experience was a crash with corrupted stack trace.
TO_CHAR(expr, fmt)
- expr: required parameter, data/time/timestamp type expression
- fmt: optional parameter, format string, supports
YYYY/YYY/YY/RRRR/RR/MM/MON/MONTH/MI/DD/DY/HH/HH12/HH24/SS and special
characters. The default value is "YYYY-MM-DD HH24:MI:SS"
In Oracle, TO_CHAR() can also be used to convert numbers to strings, but
this is not supported. This will gave an error in this patch.
Other things:
- If format strings is a constant, it's evaluated only once and if there
is any errors in it, they are given at once and the statement will abort.
Original author: woqutech
Lots of optimizations and cleanups done as part of review
