将十进制转换为日期以便使用DATENAME函数

Question

Working with an ERP database (SQL Server) that stores dates as decimal columns in YYYYMMDD format - eg 20160801 . I need to convert these values into dates so that I can use the DATENAME function to identify the day of the week corresponding to each date.

Or, if there is another way to derive the day of the week, I am all ears. The rest of the query is simple ... I just need to return an Order Number, the Order Date (the column stored as a decimal), and the day of the week corresponding to the Order Date.

EDIT (taken from a comment)

I am still missing something as I'm getting a could not be bound error:

Select CAST(OEORDD.EXPDATE AS VARCHAR(8)) 
DECLARE @dec DECIMAL(10,0)=20160801; 
SELECT CAST(CAST(@dec AS VARCHAR(8)) AS DATE) , sum(OEORDD.EXTWEIGHT) as ExtWeight 
FROM OEORDD 
GROUP BY EXPDATE

Answer 1

There is the "unserparated" datetime format, which is casteable natively. For this you'd need an 8-letter-string with yyyymmdd .

So first convert your decimal number to a string:

CAST(YourDecimalValue AS VARCHAR(8))

Then cast this to a date:

DECLARE @dec DECIMAL(10,0)=20160801;
SELECT CAST(CAST(@dec AS VARCHAR(8)) AS DATE)

UPDATE (concerning your comment)

Might be you need something like this:

SELECT  CAST(CAST(OEORDD.EXPDATE AS VARCHAR(8)) AS DATE) AS YourConvertedDate
       ,SUM(OEORDD.EXTWEIGHT) AS ExtWeight 
FROM OEORDD 
GROUP BY CAST(CAST(OEORDD.EXPDATE AS VARCHAR(8)) AS DATE)

Answer 2

You can use it for Text or Number of a week day:

DECLARE @d DECIMAL = 20160801;
SELECT DATENAME(dw,CAST(CAST(@d as VARCHAR(8)) as DATE)),
    DATENAME(d,CAST(CAST(@d as VARCHAR(8)) as DATE)),
    @d;

Answer 3

DECLARE @decimal DECIMAL(10,0)=20160801;
SELECT DATENAME(dw,CAST(convert(VARCHAR(8),@decimal) AS DATE))