How to convert a string into date format

问题

I have the following column, date_period2 in my query which displays date in yyyy-mm format but as a string.

date_period2
201304
201305
201306
201307

How can i convert that to a DATE format so I can use it to get the working days of the specific month. So for example, 201304 would be converted to 04-2013 as a DATE instead of a string.

This is my query which is calculating an expression based on the date_period2 field and it's not working because it's a string format:

SELECT TOP 1000 [date_period2]
    ,[amount]
    ,[amount]/(SELECT 20 + COUNT(*) FROM 
        (SELECT DATEADD(MONTH, DATEDIFF(MONTH, 0, [date_period2]), 28) AS theDate 
            UNION 
        SELECT DATEADD(MONTH, DATEDIFF(MONTH, 0, [date_period2]), 29) 
            UNION 
        SELECT DATEADD(MONTH, DATEDIFF(MONTH, 0, [date_period2]), 30) ) AS d 
        WHERE DATEPART(DAY, [date_period2]) > 28 AND DATEDIFF(DAY, 0, [date_period2]) % 7 < 5) AS [Weekly Charge]
    FROM [database].[dbo].[table]

The issue is the amount is being divided by 20 and not by the working days for the month-year.

Example:

date_period2    amount          charge average (amount/total working days of the month)
201304          1750359.95      87517.9975

So according to the result above the charge average is supposed to be 1750359.95/22, but instead it is being divided by 20 giving it the wrong output.

How can I either edit the query or convert the date to ensure the output is done correctly?

回答1:

Just put the string in an unambiguous date format like yyyy-mm-dd:

SELECT
    CONVERT(DATETIME,
        SUBSTRING(date_period2,1,4) + '-' 
      + SUBSTRING(date_period2,5,2) + '-01')

That will convert 201304 into 2013-04-01 which will convert directly to a DateTime.

EDIT

Since your source column is actually an integer column, a cleaner method is:

 select CONVERT(DATETIME,CONVERT(CHAR(6),date_period2)+'01')

that will convert 201304 to "20130401" whihc is still unambiguous to the datetime parser.

回答2:

You can convert date_period2 to a datetime data type with following logic.

Please change as per your need.

declare @i int
select @i = CONCAT('201305','01')
select CONVERT (datetime,convert(char(8),@i))

In CONCAT('201305','01') '01' will be constant, only '201305' will change.

回答3:

201404 can converted into 04-2014

declare @x VARCHAR(20)
SET @x = convert(varchar(7), getdate(), 126) 
select SUBSTRING(@x,6,CHARINDEX('-',@x)) +'-'+SUBSTRING(@x,0,CHARINDEX('-',@x))

来源：https://stackoverflow.com/questions/23365671/how-to-convert-a-string-into-date-format

标签

sql

sql-server

date

ssms