How to Search for Date and Time Values Using SQL Server 2000 - How to Search by Date
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Frequently. you’ll need to search a date/time column for a specific date, regardless of time. If the data in the column have been used consistently with the time component set to zero, that’s no problem. You just search for the date you’re looking for.
But consider the following table, called DateSample:
ID DateVal
-- -----------------------
1 2001-02-28 10:00:00.000
2 2002-02-28 13:58:32.823
3 2002-02-29 00:00:00.000
4 2002-02-28 00:00:00.000
As you can see, the DateVal column is used inconsistently. The third and fourth values indicate that the column might have been intended to store dates only, but the first two values indicate that this wasn’t enforced.
As a result, if you use the following query to retrieve rows with the date February 28, 2002:
SELECT * FROM DateSample
WHERE DateVal = '2002-02-28'
the result set includes only row 4 instead of both rows 2 and 4. That’s because the date literal is implicitly cast as a datetime value which, in this case, has a zero time component. Since this doesn’t exactly match the value in row 2, that row isn’t returned.
How can you get around the time component? If the query is run often, you should base the search on a range of values, as in:
SELECT * FROM DateSample
WHERE DateVal BETWEEN '2002-02-28' AND '2002-02-28 23:59:59.997'
Remember that the BETWEEN clause retrieves values that are equal to the upper and lower limits, so you can’t code the upper limit as just '2002-02-29'. If you do, then you’ll incorrectly retrieve row 3. Another way to get the same result is to use comparison operators:
SELECT * FROM DateSample
WHERE DateVal >= '2002-02-28' AND DateVal < '2002-02-29'
If the query is run infrequently (to produce a report only once a month, for instance), you can code an expression in the WHERE clause that strips the date/time value of its fractional component. For example, this query:
SELECT * FROM DateSample
WHERE CAST(FLOOR(CAST(DateVal AS float)) AS datetime) = '2002-02-28'
returns both rows 2 and 4. In addition, there are many other expressions that you can use to accomplish this same result (my SQL book, Murach’s SQL for SQL Server, covers a couple of others).
By the way, if you wished to retrieve rows with the day February 28, regardless of year, you could code the following query:
SELECT * FROM DateSample
WHERE MONTH(DateVal) = 2 AND DAY(DateVal) = 28
which retrieves rows 1, 2, and 4. Since there isn’t a way to accomplish this without using one or more functions, however, this query shouldn’t be run frequently against a production database. If you need to perform this kind of search on a query that runs often, you should change the design of the database, if possible. Then, you can create a separate, indexed column to store the portion of the date/time value that you need to search.
Next: How to Search by Time >>
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