将数据从另一表的一列插入到同一表的多列中

Question

I have a table WCR (l,j,W,C,R) with the following entries. Here, l,j are primary keys.

I have to insert data from column C of WCR into another table C(l,C1,C2) where l is the primary key. The C table will be as follows -

For each l , j=1 will be inserted in C1 , and j=2 will be inserted into C2 . But I can not generalize the queries.

I have tried statements like -

INSERT INTO C 
SELECT 1, 
C FROM WCR WHERE j=1, 
C FROM WCR WHERE j=2;

and subqueries in Insert statement like -

 INSERT INTO C 
 VALUES (1, 
         SELECT C FROM WCR WHERE j=1, 
         SELECT C FROM WCR WHERE j=2);

But none of them works in Vertica as it doesn't support subquery in INSERT statement and the first one is invalid. How can I efficiently Insert the values into C ?

Answer 1

One method uses a join :

Insert into C(l, c1, c2)
    select wcr1.l, wcr1.c, wcr2.c
    from wcr wcr1 join
         wcr wcr2
         on wcr1.l = wcr2.l and wcr1.j = 1 and wcr2.j = 2;

Another method uses conditional aggregation:

insert into c(l, c1, c2)
     select l, max(case when j = 1 then c end) as c1, max(case when j = 2 then c end)
     from wcr
     group by l;