SQL：如何仅对列中的某些字符执行选择

Question

I wanted to know how to perform the SQL SELECT operation on only a particular range of characters. For example,I've got an SQL query:

SELECT date,score from feedback GROUP BY date

Now this date is of format yyyy/mm/dd .

So I wanted to strip the days or cut out the days from it and make it yyyy/mm , thereby selecting only 0-7 characters from the date.

I've searched everywhere for the answer but could not find anything.Could I maybe do something like this?

SELECT date(7),score from feedback GROUP BY date(7)

Answer 1

In MSQL you use LEFT other use substring

SELECT LEFT('abcdefg',2);
-- 
ab 

So in your case

SELECT LEFT(date,7), score
FROM feedback
GROUP BY LEFT(date,7)

But again things will be much easier if you use a date field instead a text field.

Answer 2

Assuming that your date field is an actual date field (or even a datetime field) the following solution would work:

select left(convert(date ,getdate()),7) as Year_Month

Changing getdate() to your date field, it would look like:

select left(convert(date , feedback.date),7) as Year_Month

Both queries return the following:

2016-01