SQL Server：获取当前月份和前几个月

Question

I have a table with a column dateE that is formatted as nvarchar(20) and contains dates in the format yyyy-mm-dd. The below stored procedure fetches all records from this table with dateE from Apr 2014:

BEGIN
    SET NOCOUNT ON;
    SELECT      cat,
                COUNT(*) AS groupCount
    FROM        Log_PE 
    WHERE       dateE LIKE '2014-04%'
    GROUP BY    cat
    ORDER BY    groupCount desc, cat
END

How can I change this so that I don't have to hard-code the date and instead it always uses the current year and month for this ?

In addition, I would like to use the same stored procedure to also fetch the same data from the previous three months (in this case Jan, Feb, March 2014) so that in the end I have a ranking like in my example but for each of the above months.

Can anyone here help me with this ?

Many thanks in advance, Tim.

Answer 1

Instead of comparing strings, compare dates. Try this:

SELECT      cat, COUNT(*) AS groupCount
FROM        Log_PE 
WHERE       CONVERT(DATE, dateE, 120) >= 
              CONVERT(DATE, CONVERT(VARCHAR(6), GETDATE(), 112) + '01', 112)

GROUP BY    cat
ORDER BY    groupCount desc, cat

Explanation:

--Convert your string date column to a date type (yyyy-mm-dd --> 120)
CONVERT(DATE, dateE, 120)

--Convert the current date to yyyymmdd format (style 112) 
--and get the first 6 characters. ie; Year and month
CONVERT(VARCHAR(6), GETDATE(), 112) 

--Add `'01'` to the `yyyymm` and convert back to a date type
CONVERT(DATE, CONVERT(VARCHAR(6), GETDATE(), 112) + '01', 112) 

Answer 2

尝试使用此日期表达式：

...where dateE LIKE convert(varchar (7), GETDATE(), 20) + '%'