如何在sql中检查第一列的行是否大于第二列（使用IF语句）

Question

I wrote a query to create a table with one column

CREATE TABLE ORDER( 
   Order_Date DATE NOT NULL
)

I inserted two values into the column

--Order_Date--
2018-05-21
2018-01-21

How to check if the first row is greater or less than the second row using IF statement?

Answer 1

SQL tables represent unordered sets. There is no "first" row or "second" row in a table.

You can do what you want if you include an identity column:

CREATE TABLE ORDERS ( 
   OrderId IDENTITY(1, 1) PRIMARY KEY,
   Order_Date DATE NOT NULL
);

Now, you can see if OrderId and OrderDate are in the same order. Something like:

select (case when max(case when seqnum = 1 then order_date end) >
                  max(case when seqnum = 2 then order_date end)
             then 'greater than'
             when max(case when seqnum = 1 then order_date end) =
                  max(case when seqnum = 2 then order_date end)
             then 'equal'
             when max(case when seqnum = 1 then order_date end) <
                  max(case when seqnum = 2 then order_date end)
             then 'less than'
        end) as comparison
from (select o.*, row_number() over (order by OrderId) as seqnum
      from orders o
     ) o;

Notice that I also renamed the table to Orders . Order is a really bad name for a table because it is a SQL keyword and a reserved word as well.