Joanne Pham wrote:
I have two question regarding DATETIME column data type:
1 ) Should I store my COLUMN as INTEGER instead of DATETIME. Is it easier if this column type is INTEGER vs DATETIME then
do the conversion in the GUI code to convert from INTEGER TO DATETIME.
2) And if I store as DATETIME then What is the command to bind this column
type as DATETIME.
For the INTEGER the bind command is : sqlite3_bind_int but I don't know if the column is DATETIME
then what is the command to bind this column.
Joanne,
You need to familiarize yourself with SQLite's type system. See
http://www.sqlite.org/datatype3.html for the fundamental data types that
SQLite supports, and how it handles them.
A column with a declared type of DATETIME, has an column affinity of
NUMERIC. And such a column can store any of the supported datatypes.
The preferred method of storing time and date information in SQLite is
using a Julian Day number (see http://en.wikipedia.org/wiki/Julian_Day)
which is floating point number where the integral part represents the
date, and the fractional part represents the time. SQLite can use this
format to efficiently order and compare dates and times in SQL queries.
You can use the builtin date and time functions (see
http://www.sqlite.org/cvstrac/wiki?p=DateAndTimeFunctions) to convert
the stored Julian Day numbers to standard (at least nearly ISO-8601
standard) date and time strings for display or manipulation by the
language you are using to drive SQLite.
If you use Julian Day numbers you can declare your timetsamp column REAL
or FLOAT (or possibly JULIAN or even DATETIME if you wish), and then use
the sqlite3_bind_double() and sqlite3_column_double() to insert and
extract the raw floating point values, or sqlite3_column_text() to
extract a time or date strings returned by the builtin conversion functions.
create table test (id integer primary key, data text, created julian);
Note you can't use the "default current_timestamp" clause because it
will insert a string version of the date and time. If you want automatic
inserts of a Julian Day number you need to use a trigger.
create trigger set_created after insert on test begin
update test set created = julianday('now') where rowid = new.rowid;
end;
If you add an index on the created column you can quickly search for
dates and times, or date or time ranges.
create index created_idx on test(created);
You can now easily search for ranges and convert the result for display.
select id, data from test where created > julianday(date('now', '-30
days'));
select id, data, date(created) from test order by created desc limit 1;
Most of the same things can be accomplished if you store the ISO-8601
string verisons of the date and time in the database, but that requires
19 or more bytes per timestamp (and the timestamp value is duplicated in
each index as well), whereas the Julian Day number requires only 8 bytes
per timestamp.
HTH
Dennis Cote
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