How do I specify date literal when writing SQL query from SQL Server that is linked to Oracle?

Question

I have a SQL Server 12.0 database that is linked to an Oracle 12.1 database.

I want to create a view in the SQL Server database that returns data from an Oracle table filtered by date. The Oracle table has an index on the date column.

A query that works successfully is:

select * from ORADB..SCHEMA.MYTABLE where MYDATE >= '20140701';

However this runs very slowly. I assume it is because the comparison is taking place in SQL Server so every row is being returned.

If I go:

DECLARE @earliest date = '20140701';
select * from ORADB..SCHEMA.MYTABLE where MYDATE >= @earliest;

Then it runs fast, presumably because the condition is being passed to Oracle so the Oracle index on the table is being used.

My problem is that I want to create a view. I can't find a way of using the second version of the code to create a view. If I simply do:

create myview as select * from ORADB..SCHEMA.MYTABLE where MYDATE >= '20140701';

Then it runs slowly.

Is there another format for the date literal that SQL Server will pass to Oracle, or is there another solution? I wondered also if it was to do with the parameters used in creating the link to Oracle. For reference they are:

USE [master]
GO
EXEC master.dbo.sp_addlinkedserver @server = N'ORADB', @srvproduct=N'Oracle', @provider=N'OraOLEDB.Oracle', @datasrc=N'DPDB'
EXEC master.dbo.sp_addlinkedsrvlogin @rmtsrvname=N'ORADB',@useself=N'False',@locallogin=NULL,@rmtuser=N'MYUSER',@rmtpassword='#######'
GO
EXEC master.dbo.sp_serveroption @server=N'ORADB', @optname=N'collation compatible', @optvalue=N'false'
GO
EXEC master.dbo.sp_serveroption @server=N'ORADB', @optname=N'data access', @optvalue=N'true'
GO
EXEC master.dbo.sp_serveroption @server=N'ORADB', @optname=N'dist', @optvalue=N'false'
GO
EXEC master.dbo.sp_serveroption @server=N'ORADB', @optname=N'pub', @optvalue=N'false'
GO
EXEC master.dbo.sp_serveroption @server=N'ORADB', @optname=N'rpc', @optvalue=N'false'
GO
EXEC master.dbo.sp_serveroption @server=N'ORADB', @optname=N'rpc out', @optvalue=N'false'
GO
EXEC master.dbo.sp_serveroption @server=N'ORADB', @optname=N'sub', @optvalue=N'false'
GO
EXEC master.dbo.sp_serveroption @server=N'ORADB', @optname=N'connect timeout', @optvalue=N'0'
GO
EXEC master.dbo.sp_serveroption @server=N'ORADB', @optname=N'collation name', @optvalue=null
GO
EXEC master.dbo.sp_serveroption @server=N'ORADB', @optname=N'lazy schema validation', @optvalue=N'false'
GO
EXEC master.dbo.sp_serveroption @server=N'ORADB', @optname=N'query timeout', @optvalue=N'0'
GO
EXEC master.dbo.sp_serveroption @server=N'ORADB', @optname=N'use remote collation', @optvalue=N'true'
GO
EXEC master.dbo.sp_serveroption @server=N'ORADB', @optname=N'remote proc transaction promotion', @optvalue=N'true'
GO

EDIT: I just found a very similar question: Forcing a SQL Remote Query to filter remotely instead of locally

Answer 1

I prefer the ODBC format:

--DateTime
SELECT {ts'2015-09-20 12:30:00'}
--Time (however this comes with "today"-time)
SELECT {t'12:30:00'}
--Date
SELECT {d'2015-09-20'}
GO

The simple date literal is not culture independent...

SET LANGUAGE ENGLISH;
SELECT CAST('2014-09-13' AS DATETIME);
GO
SET LANGUAGE GERMAN;
SELECT CAST('2014-09-13' AS DATETIME);--ERROR: there's no month "13"
GO

But it works - however - with target type DATE (this difference is rather weird...):

SET LANGUAGE ENGLISH;
SELECT CAST('2014-09-13' AS DATE);
GO
SET LANGUAGE GERMAN;
SELECT CAST('2014-09-13' AS DATE);--ERROR: there's no month "13"
GO

Thx to lad2025 I want to add for completness the "full" ISO 8601, which works fine:

SET LANGUAGE ENGLISH;
SELECT CAST('2014-09-13T12:30:00' AS DATETIME);
GO
SET LANGUAGE GERMAN;
SELECT CAST('2014-09-13T12:30:00' AS DATETIME);
GO

Answer 2

I would recommend using the full ISO 8601 format as suggested by @lad2025:

'2017-10-06T14:57:23'

This is superior to the ODBC format suggested by @Shnugo.

In SQL Server 2014 at least, the ODBC format will not work for dates prior to 1753-01-01 (e.g. those dates outside of the range of the old DATETIME data type), whereas the ISO 8601 format does.

To test this yourself, try the following queries:

--This will work
DECLARE @DateISO DATE = '0001-01-01T00:00:00';
SELECT @DateISO;

--This will also work
DECLARE @DatetimeISO DATETIME2 = '0001-01-01T00:00:00';
SELECT @DatetimeISO;

--This will not work
DECLARE @DateODBC DATE = {D '0001-01-01'};
SELECT @DateODBC;

--This will also not work
DECLARE @DatetimeODBC DATETIME2 = {ts '0001-01-01 00:00:00'};
SELECT @DatetimeODBC;

Even if you don't think the dates you're working with will ever be before the year 1753, it's a good habit to be in. I ran into this while looking at setting up a calendar table to reference in queries.

Answer 3

If the query is running on Oracle database, then I suggest use the ANSI date literal which uses a fixed Format YYYY-MM-DD.

For example,

DATE '2015-10-20'

In Oracle, '20140701' is a string and not a DATE. You might just be lucky to see an implicit data type conversion and get the result based on the locale-specific NLS settings of your client. You should always avoid it, and explicitly convert the string into date for date comparisons.