Postgres 9.4

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create table t1 (id int primary key, foo int, bar int)

CREATE TABLE


insert into t1 values
(1, 3, 4),
(2, 5, 6),
(3, 4, 7),
(4, 3, 3),
(5, 2, 5)

INSERT 0 5


create table t2 (id int primary key, foo int, bar int)

CREATE TABLE


insert into t2 values
(1, 3, 4),
(2, 4, 6),
(3, 4, 7),
(4, 3, 5),
(5, 3, 6)

INSERT 0 5


SELECT t1.id,
       CONCAT_WS(' ',
                 CASE WHEN t1.foo != t2.foo THEN 'foo' END,
                 CASE WHEN t1.bar != t2.bar THEN 'bar' END
                 ) AS reason
FROM t1
JOIN t2 ON t2.id = t1.id
WHERE t1.foo != t2.foo OR t1.bar != t2.bar


id
reason


2
foo

4
bar

5
foo bar



SELECT 3