How to compare sqlite TIMESTAMP values

Question

I have an Sqlite database in which I want to select rows of which the value in a TIMESTAMP column is before a certain date. I would think this to be simple but I can\'t get

Answer 1

SQLite's support for date/time types is very limited. You may have to roll-your-own method for maintaining time information. At least, that's what I did.

You can define your own stored-functions for doing comparisons using the SQLite create_function() API.

Answer 2

As best I can tell, it's entirely reasonable to include a timezone specifier; see the text "formats 2 through 10 can . . ." at http://www.sqlite.org/lang_datefunc.html However, the issue is that only the date functions interpret timestamps as dates. So for actual comparison, you need to either pass the timestamp through a date function or store things such that string comparison works. One approach would be to code your application such that you called datetime on every value that you insert and on every literal value in a select statement. However, simply not including the time zone as suggested by the existing answer may be easier in many applications.

Answer 3

The issue is with the way you've inserted data into your table: the +0200 syntax doesn't match any of SQLite's time formats:

1. YYYY-MM-DD
2. YYYY-MM-DD HH:MM
3. YYYY-MM-DD HH:MM:SS
4. YYYY-MM-DD HH:MM:SS.SSS
5. YYYY-MM-DDTHH:MM
6. YYYY-MM-DDTHH:MM:SS
7. YYYY-MM-DDTHH:MM:SS.SSS
8. HH:MM
9. HH:MM:SS
10. HH:MM:SS.SSS
11. now
12. DDDDDDDDDD

Changing it to use the SS.SSS format works correctly:

sqlite> CREATE TABLE Foo (created_at TIMESTAMP);
sqlite> INSERT INTO Foo VALUES('2010-05-28T15:36:56+0200');
sqlite> SELECT * FROM Foo WHERE foo.created_at < '2010-05-28 16:20:55';
sqlite> SELECT * FROM Foo WHERE DATETIME(foo.created_at) < '2010-05-28 16:20:55';
sqlite> INSERT INTO Foo VALUES('2010-05-28T15:36:56.200');
sqlite> SELECT * FROM Foo WHERE DATETIME(foo.created_at) < '2010-05-28 16:20:55';
2010-05-28T15:36:56.200

If you absolutely can't change the format when it is inserted, you might have to fall back to doing something "clever" and modifying the actual string (i.e. to replace the + with a ., etc.).

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(original answer)

You haven't described what kind of data is contained in your CREATED_AT column. If it indeed a datetime, it will compare correctly against a string:

sqlite> SELECT DATETIME('now');
2010-05-28 16:33:10
sqlite> SELECT DATETIME('now') < '2011-01-01 00:00:00';
1

If it is stored as a unix timestamp, you need to call DATETIME function with the second argument as 'unixepoch' to compare against a string:

sqlite> SELECT DATETIME(0, 'unixepoch');
1970-01-01 00:00:00
sqlite> SELECT DATETIME(0, 'unixepoch') < '2010-01-01 00:00:00';
1
sqlite> SELECT DATETIME(0, 'unixepoch') == DATETIME('1970-01-01 00:00:00');
1

If neither of those solve your problem (and even if they do!) you should always post some data so that other people can reproduce your problem. You should even feel free to come up with a subset of your original data that still reproduces the problem.