Adding support for the "FM" format in function TO_CHAR(date_time, fmt).
"FM" in the format string disables padding of all components following it.
So now TO_CHAR() works as follows:
- By default string format components DAY (weekday name) and
MONTH (month name) are right-padded with spaces to the maximum
possible DAY and MONTH name lengths respectively,
according to the current locale specified in @@lc_time_names.
So for example, with lc_time_names='en_US' all month names are
right-padded with spaces up to 9 characters ('September' is the longest).
SET lc_time_names='en_US';
SELECT TO_CHAR('0001-02-03', 'MONTH'); -> 'February ' (padded to 9 chars)
NEW: When typed after FM, DAY and MONTH names are not right-padded
with trailing spaces any more:
SET lc_time_names='en_US';
SELECT TO_CHAR('0001-02-03', 'FMMONTH'); -> 'February' (not padded)
- By default numeric components YYYY, YYY, YY, Y, DD, H12, H24, MI, SS
are left-padded with leading digits '0' up to the maximum possible
number of digits in the component (e.g. 4 for YYYY):
SELECT TO_CHAR('0001-02-03', 'YYYY'); -> '0001' (padded to 4 chars)
NEW: When typed after FM, these numeric components are not left-padded
with leading zeros any more:
SELECT TO_CHAR('0001-02-03', 'FMYYYY'); -> '1' (not padded)
- If FM is specified multiple times in a format string,
every FM negates the previous padding state:
* an odd FM disables padding
* an even FM enables padding
Implementation details:
- Adding a helper class Date_time_format_oracle.
- Adding a helper method Date_time_format_oracle::append_lex_cstring()
- Moving the function append_val() to Date_time_format_oracle as a method.
- Moving the function make_date_time_oracle() to Date_time_format_oracle
as a method format().
- Adding helper methods month_name() and day_name() in class MY_LOCALE,
to return the corresponding components as LEX_CSTRINGs.
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
