使用SQL Server中的格式将nvarchar转换为最新格式

Question

I'm using SQL Server Management Studio. There is one table in my database containing dates which are stored as nvarchar(255). I want to migrate the data of this table to a new table which I call Converted_Dates and store this data as date. Also, I want them all to be formatted like this YYYY-MM-DD

Currently the Dates table looks like this:

**Dates**
15/6/2011 
16/6/2011
2013-03-30
2013-04-16
...

I want the new table to look like this:

**Converted_Dates**
2011-06-15
2011-06-16
2013-03-30
2013-04-16
...

I execute this query but formatting of dates remains the same, only the data type changes from nvarchar(255) to date.

    USE [reporting_database]
    GO
    INSERT INTO [dbo].[Converted_Dates]
    SELECT
        cast(Dates as date)


        FROM [dbo].[Dates]
    GO

Any advice on how to cast the data from the old table to a new one in a preferred format?

Answer 1

The value of date and datetime data type is not stored with format in sql server. If you want to see the date in a different format you can manipulate the way that date and datetime data types are displayed when converted to a varchar (or nvarchar , nchar , char ) data type using some built in functions.

You should store your dates as date data type, and if you can format them at the application level, do so there. If you must format them in sql, then use convert() styles .

select convert(char(10),getdate(),120) 

returns: 2017-05-01

---

In sql server 2012+ you can use format()

 select format(getdate(),'yyyy-MM-dd') 

returns: 2017-05-01

But format() is much slower, take a look here: format() is nice and all, but… - Aaron Bertrand