Side-by-side comparison of data by year in SQL

问题

I have table similar to the following:

Year | Product |  Value
2006   A          10
2006   B          20
2006   C          30
2007   A          40
2007   B          50
2007   C          60

I would like a query that would return the following comparison

Product | 2006 Value | 2007 Value
A         10           40
B         20           50
C         30           60

What are the options to do so? Can it be done without joins?

I'm working with DB2, but answers in all SQL types would be helpful.

回答1:

select Product, 
    max(case when Year = 2006 then Value end) as [2006 Value], 
    max(case when Year = 2007 then Value end) as [2007 Value] 
from MyTable
group by Product
order by Product

回答2:

A simple cross tab query should do it

SELECT DISTINCT (year), PRODUCT,
sum (case when year = 2006 then VALUE else 0 end ) as [2006 Value]
sum (case when year = 2007 then value else 0 end ) as [2007 value]
from table
group by year, product

Check the syntax, but that's the basic idea. There is really no need to join.

回答3:

You've already got some answers that don't use a join, but just for comparison here's an alternative that does use a join:

SELECT
    T1.Product,
    T1.Value AS [2006 Value],
    T2.Value AS [2007 Value]
FROM Table1 T1
JOIN Table1 T2
ON T1.Product = T2.Product
AND T1.Year = 2006
AND T2.Year = 2007

I'm working with DB2, but answers in all SQL types would be helpful.

Here's a solution using PIVOT that SQL Server supports:

SELECT
    Product,
    [2006] AS [2006 Value],
    [2007] AS [2007 Value]
FROM Table1
PIVOT(MAX(Value) FOR Year IN ([2006], [2007]))
AS p;

来源：https://stackoverflow.com/questions/3040680/side-by-side-comparison-of-data-by-year-in-sql

标签

sql

db2

pivot