updating for several columns with distinct conditions

Question

I have INSERT statement where values are provided through SELECT from other table. ON CONFLICT I'm updating several columns. I'm just wondering if is possible to SET each column matching unique condition

Now I have solution which work, however it isn't ideal.

Basically something like this would match my desired result..

WITH table_a (
 --joining two tables
)

INSERT INTO table_b
SELECT * FROM table_a
ON CONFLICT
ON CONSTRAINT table_b_pkey DO UPDATE
SET column_a = EXCLUDED.column_a
WHERE table_b.column_a < EXCLUDED.column_a
OR 
SET column_b = EXCLUDED.column_b
WHERE table_b.column_b < EXCLUDED.column_b

Answer 1

Use CASE, e.g.:

INSERT INTO table_b
SELECT * FROM table_a
ON CONFLICT
ON CONSTRAINT table_b_pkey DO UPDATE
SET 
    column_a = CASE 
        WHEN table_b.column_a < EXCLUDED.column_a 
        THEN EXCLUDED.column_a 
        ELSE table_b.column_a END,
    column_b = CASE 
        WHEN table_b.column_b < EXCLUDED.column_b 
        THEN EXCLUDED.column_b 
        ELSE table_b.column_b END