Question

running :

SELECT CONVERT(VARCHAR(20), GETDATE(), 100)

will result :

Jan  4 2012  1:25PM

Ive been knowing this for years.

However , yesterday, while I was driving , I thought to my self :

Hey! I gave him the format of 103 which is for datetime format ,

But I didnt actually TOLD the convert that Im passing also a datetime
object ! ( e.g. getdate()))

So ive tried :

SELECT CONVERT(VARCHAR(20), 'lalala', 100)

And the result was :

lalala

so , now Im trying to convert ‘lalala’ to string via datetime format (103).

which is ( by logic) should give me exception.

but it is not.

Any reasonable explanation ?

Answer 1

CONVERT takes into account both the target type and the expression’s type to see whether the third argument should be considered. If you are converting a datetime to a string or the other way round, the third argument is considered. In your example, a string is converted to a string and so the third argument is ignored.

Consider this:

SELECT 1, CONVERT(datetime, '03/01/2011', 103)
SELECT 2, CONVERT(datetime, '03/01/2011', 101)
SELECT 3, CONVERT(varchar, '03/01/2011', 103)
SELECT 4, CONVERT(varchar, '03/01/2011', 101)

Here are the results:

--- -----------------------
1   2011-01-03 00:00:00.000

--- -----------------------
2   2011-03-01 00:00:00.000

--- ------------------------------
3   03/01/2011

--- ------------------------------
4   03/01/2011

As you can see, the last two ‘conversions’ didn’t change anything, because both the source and the target type were varchar, even though the expression did look like a date/datetime.

Reference:

• CAST and CONVERT (Transact-SQL)