ruby on rails 3 - How do I match an entire day to a datetime field?

Question

I have a table for matches. The table has a column named matchdate, which is a datetime field.

If I have 3 matches on 2011-12-01:

• 2011-12-01 12:00:00
• 2011-12-01 13:25:00
• 2011-12-01 16:00:00

How do I query that? How do I query all matches on 1 single date?

I have looked at date_trunc(), to_char(), etc.
Isn't there some "select * where datetime in date" function?

Answer 1

Cast your timestamp value to date if you want simple syntax. Like this:

SELECT *
FROM   tbl
WHERE  timestamp_col::date = '2011-12-01';  -- date literal

However, with big tables this will be faster:

SELECT *
FROM   tbl
WHERE  timestamp_col >= '2011-12-01 0:0'    -- timestamp literal
AND    timestamp_col <  '2011-12-02 0:0';

Reason: the second query does not have to transform every single value in the table and can utilize a simple index on the timestamp column. The expression is sargable.

Note excluded the upper bound (< instead of <=) for a correct selection.
You can make up for that by creating an index on an expression like this:

CREATE INDEX tbl_ts_date_idx ON tbl (cast(timestamp_col AS date));

Then the first version of the query will be as fast as it gets.