How can I Pivot a table in DB2? [duplicate]

问题:

This question already has an answer here:

• Pivoting in DB2 3 answers

I have table A, below, where for each unique id, there are three codes with some value.

 ID    Code    Value
---------------------
 11       1       x
 11       2       y
 11       3       z
 12       1       p
 12       2       q
 12       3       r
 13       1       l
 13       2       m
 13       3       n

I have a second table B with format as below:

Id   Code1_Val   Code2_Val    Code3_Val

Here there is just one row for each unique id. I want to populate this second table B from first table A for each id from the first table.

For the first table A above, the second table B should come out as:

Id   Code1_Val   Code2_Val    Code3_Val
---------------------------------------------
11       x          y             z
12       p          q             r
13       l          m             n

How can I achieve this in a single SQL query?

回答1:

If your version doesn't have DECODE(), you can also use this:

INSERT INTO B (id, code1_val, code2_val, code3_val)  
WITH Ids (id) as (SELECT DISTINCT id
                  FROM A) -- Only to construct list of ids

SELECT Ids.id, a1.value, a2.value, a3.value
FROM Ids -- or substitute the actual id table
JOIN A a1
     ON a1.id = ids.id
        AND a1.code = 1
JOIN A a2
     ON a2.id = ids.id
        AND a2.code = 2
JOIN A a3
     ON a3.id = ids.id
        AND a3.code = 3

(Works on my V6R1 DB2 instance, and have an SQL Fiddle Example).

回答2:

   select Id,                                              
      max(case when Code = '1' then Value end) as Code1_Val,  
      max(case when Code = '2' then Value end) as Code2_Val,  
      max(case when Code = '3' then Value end) as Code3_Val   
      from TABLEA                                     
      group by Id                                            

回答3:

SELECT Id,
max(DECODE(Code, 1, Value)) AS Code1_Val,
max(DECODE(Code, 2, Value)) AS Code2_Val,
max(DECODE(Code, 3, Value)) AS Code3_Val
FROM A
group by Id

回答4:

Here is a SQLFiddle example

insert into B (ID,Code1_Val,Code2_Val,Code3_Val)
select Id, max(V1),max(V2),max(V3) from
(
select ID,Value V1,'' V2,'' V3 from A where Code=1
union all
select ID,'' V1, Value V2,'' V3 from A where Code=2
union all
select ID,'' V1, '' V2,Value V3 from A where Code=3
) AG
group by ID

回答5:

Here is the SQL Query:

insert into pivot_insert_table(id,code1_val,code2_val, code3_val) 
select * from (select id,code,value from pivot_table)
pivot(max(value) for code in (1,2,3)) order by id ;

回答6:

 WITH Ids (id) as 
 (
  SELECT DISTINCT id FROM A
  )
 SELECT Ids.id, 
 (select sub.value from A sub where Ids.id=sub.id and sub.code=1 fetch first rows only) Code1_Val,

 (select sub.value from A sub where Ids.id=sub.id and sub.code=2 fetch first rows only) Code2_Val,

 (select sub.value from A sub where Ids.id=sub.id and sub.code=3 fetch first rows only) Code3_Val
 FROM Ids

回答7:

You want to pivot your data. Since DB2 has no pivot function, yo can use Decode (basically a case statement.)

The syntax should be:

SELECT Id,
   DECODE(Code, 1, Value) AS Code1_Val,
   DECODE(Code, 2, Value) AS Code2_Val,
   DECODE(Code, 3, Value) AS Code3_Val,
FROM A