Convert() SQL Server to Oracle

Question

I have this query on SQL Server, the goal of this query is to set the milliseconds to 000, for instance,

Before this Query: 2017-06-01 11:53:00.123
After: 2017-06-01 11:53:00.000

UPDATE table1 
  SET ValidFrom = CONVERT(DATETIME, CONVERT(CHAR(19), ValidFrom, 126)) 
WHERE ValidFrom IS NOT NULL;

ValidFrom is a column on the database that it is a datetime.

There is a Convert command on Oracle but it doesn't work with Datetime.

How can I translate this to Oracle?

Answer 1

• Converting any strongly-typed date , datetime , datetimeoffset , etc column to char / varchar is a code-smell and a strong hint that you're doing something wrong because you should never need to format-dates to perform date/time processing in SQL.
• Oracle doesn't have a datetime type like SQL Server does, instead it has a timestamp type (which has absolutely nothing to do with SQL Server's own timestamp type which is an alias for rowversion but I digress).
• Oracle's timestamp type is parameterised to specify the amount of precision for sub-second resolution - so simply CAST ing your value to timestamp(0) will effectively zero-out the milliseconds component.
• You can also use the EXTRACT function to obtain the integer value ( 0-999 ) of the milliseconds component of a timestamp value.

UPDATE
    table
SET
    ValidFrom = CAST( ValidFrom AS timestamp(0) )
WHERE
    ValidFrom IS NOT NULL

---

Here's a working demo in SQLFiddle, using Oracle 11g R2 :

Build Schema Script:

CREATE TABLE testTable (
    ValidFrom timestamp(7) NOT NULL
);

INSERT INTO testTable ( ValidFrom )
WITH v AS ( 
    SELECT TIMESTAMP '1997-01-08 11:11:11.111' AS ts FROM dual UNION ALL 
    SELECT TIMESTAMP '1997-02-09 12:22:22.222' AS ts FROM dual UNION ALL 
    SELECT TIMESTAMP '1997-03-10 13:33:33.333' AS ts FROM dual UNION ALL 
    SELECT TIMESTAMP '1997-04-11 14:44:44.444' AS ts FROM dual
) 
SELECT ts FROM v

Query script:

SELECT
  ValidFrom,
  CAST( ValidFrom AS timestamp(0) ) AS ValidFrom_withoutMilliseconds,
  ( ValidFrom - CAST( ValidFrom AS timestamp(0) ) ) AS diff
FROM
  testTable

//

UPDATE
    testTable
SET
    ValidFrom = CAST( ValidFrom AS timestamp(0) )
WHERE
    ValidFrom IS NOT NULL

//

SELECT
  ValidFrom,
  CAST( ValidFrom AS timestamp(0) ) AS ValidFrom_withoutMilliseconds,
  ( ValidFrom - CAST( ValidFrom AS timestamp(0) ) ) AS diff
FROM
  testTable

• Today I learned that // is the query separator, which is separate from the "query terminator" in Oracle.
• To my surprise, Oracle Database still doesn't support milliseconds with EXTRACT , fortunately that isn't necessary for this query.