Update table multiple column values from another table multiple rows by matching IDs

Question

I'm Trying to update Table-A (Col1, Col2, Col3) values from Table B (Row1, Row2, Row3) by matching ColID & mapping_id in Row.

Table - A

ColID	Col1	Col2	Col3
A	null	null	null
B	null	null	null
C	null	null	null

Table - B

RowID	Value	mapping_id	Col
1	1a (this value goes to A-Col1)	A	Col1
2	2a (this value goes to A-Col2)	A	Col2
3	3a (this value goes to A-Col3)	A	Col3
4	1b (this value goes to B-Col1)	B	Col1
5	2b (this value goes to B-Col2)	B	Col2
6	3b (this value goes to B-Col3)	B	Col3

Expected Output

ColID	Col1	Col2	Col3
A	1a	2a	3a
B	1b	2b	3b
C	null	null	null

My query:

update Table-A
SET Col1 = (select value
            from Table-B
            where Table-A.ColID = Table-B.mapping.id
            and TableB.Col = 'Col1');

When I run this code it's updating Table-A Col1

Like this

ColID	Col1	Col2	Col3
A	1a	null	null
B	1b	null	null
C	null	null	null

I'm having more than 30 columns in table, I can't update one by one.

Answer 1

You can first apply a pivoting operation using:

• CASE operations to extract the corresponding " Value_ " values for each of the columns
• MAX operations to aggregate rows and select only non-null " Col1 ", " Col2 ", " Col3 " values

Once you have your " Table B " so wrangled (which we're calling " cte " ), you can carry out the UPDATE statement and set " TableA.Col " to the corresponding " cte.Col " values. You can match values between two tables inside an UPDATE statement with a JOIN operation.

WITH cte AS (
    SELECT mapping_id, 
           MAX(CASE WHEN Col = 'Col1' THEN Value_ END) AS Col1,
           MAX(CASE WHEN Col = 'Col2' THEN Value_ END) AS Col2,
           MAX(CASE WHEN Col = 'Col3' THEN Value_ END) AS Col3
    FROM tabB
    GROUP BY mapping_id
)
UPDATE     tabA
INNER JOIN cte
        ON tabA.ColID = cte.mapping_id
SET tabA.Col1 = cte.Col1,
    tabA.Col2 = cte.Col2,
    tabA.Col3 = cte.Col3;

Check the demo here .