Does Sqlite3 Understand 12 Hours time format? - sqlite

Question

I'm create a Table as follows:
CREATE TABLE IF NOT EXISTS problem(`row_id` INTEGER PRIMARY KEY, `datetime` TEXT)
I insert the values into table
INSERT INTO problem(`row_id`, `datetime`) VALUES
(1, '2021-01-03 12:50 PM'),
(2, '2021-01-03 04:55 PM');
Select the values ordered by column name
SELECT *FROM problem ORDER BY `datetime`
Reselt is here:
row_id datetime
2 2021-01-03 04:55 PM
1 2021-01-03 12:50 PM
In my view, row id 1 will be the first item and row id 2 will be the second entry.
If it does not understand 12 hours time what's the solution?

Answer 1

Does Sqlite3 Understand 12 Hours time format?
No, it understands 24 hour time format (see link below).
If it does not understand 12 hours time what's the solution?
The correct solution would be to store the data in a recognized format as per https://sqlite.org/lang_datefunc.html#time_values
Using a recognised format means that you can then take advantage of SQLite knowing that the column is a date/time/datetime column and thus utilise date time functions as well as being suitable for ordering and comparison.
An example, utilising your dates (note the use of 24 hour times when storing) to get the dates in the 12 hour format based upon 12:00 being PM is :-
DROP TABLE IF EXISTS problem;
CREATE TABLE IF NOT EXISTS problem(`row_id` INTEGER PRIMARY KEY, `datetime` TEXT);
INSERT INTO problem(`row_id`, `datetime`) VALUES
(1, '2021-01-03 12:50'),
(2, '2021-01-03 10:50'),
(3, '2021-01-03 13:55'),
(4, '2021-01-03 16:55'),
(5, '2021-01-03 00:55');
SELECT `row_id`,
date(`datetime`)||
CASE
/* Handle times that are 13:00 or greater i.e. use PM and subtract 12 hours from the stored time */
WHEN time(`datetime`) > '12:59'
THEN ' '||strftime('%H:%M',`datetime`,'-12 hours')||' PM'
/* Handle times that have 12 as the hour i.e. use PM with stored time */
WHEN time(`datetime`) > '11:59'
THEN ' '||strftime('%H:%M',`datetime`)||' PM'
/* ELSE use AM with stored time */
ELSE ' ' || strftime('%H:%M',`datetime`)||' AM'
END
AS `newdatetime` /* Note alias otherwise column name is generated according to column selection code */
FROM problem ORDER BY `datetime`;
Note that the order is as per the datetime column which being in a sortable format is always correct as the 24 hour format is used.
Note that the precision is only suitable for hh:mm e.g. if seconds then 12:59 should be 12:59:59 .....
The result of running the above is :-
The above utilises some of the Date Time Functions found at https://sqlite.org/lang_datefunc.html
The date function returns the date in yyyy-mm-dd format,
The time
function returns the time in hh:mm:ss format,
strftime is the
underlying function that can return a value in many formats based
upon a formatting string and modifiers.
All 3 use a take a time_value
(often the respective column containing the time).
You could perhaps simplify matters by utilising a function in whatever programming language your are using that converts from 24 hour to 12 hour. This could reduce the need for the complicated queries.