DateTime2 vs DateTime in SQL Server

Question

Which one:

• datetime
• datetime2

is the recommended way to store date and time in SQL Server 2008+?

I\'m aware of differ

Answer 1

Old Question... But I want to add something not already stated by anyone here... (Note: This is my own observation, so don't ask for any reference)

Datetime2 is faster when used in filter criteria.

TLDR:

In SQL 2016 I had a table with hundred thousand rows and a datetime column ENTRY_TIME because it was required to store the exact time up to seconds. While executing a complex query with many joins and a sub query, when I used where clause as:

WHERE ENTRY_TIME >= '2017-01-01 00:00:00' AND ENTRY_TIME < '2018-01-01 00:00:00'

The query was fine initially when there were hundreds of rows, but when number of rows increased, the query started to give this error:

Execution Timeout Expired. The timeout period elapsed prior
to completion of the operation or the server is not responding.

I removed the where clause, and unexpectedly, the query was run in 1 sec, although now ALL rows for all dates were fetched. I run the inner query with where clause, and it took 85 seconds, and without where clause it took 0.01 secs.

I came across many threads here for this issue as datetime filtering performance

I optimized query a bit. But the real speed I got was by changing the datetime column to datetime2.

Now the same query that timed out previously takes less than a second.

cheers

Answer 2

while there is increased precision with datetime2, some clients doesn't support date, time, or datetime2 and force you to convert to a string literal. Specifically Microsoft mentions "down level" ODBC, OLE DB, JDBC, and SqlClient issues with these data types and has a chart showing how each can map the type.

If value compatability over precision, use datetime