WITH t1 AS (
    SELECT
        entity,
        header_id,
        net_amt
    FROM
        XXTB_JE_TRX
    WHERE
        net_amt < 0
), t2 AS (
    SELECT
        entity,
        header_id,
        net_amt
    FROM
        XXTB_JE_TRX
    WHERE
        net_amt > 0
)
SELECT
    t1.entity,
    t1.header_id,
    t1.net_amt,
    t2.entity related_entity
FROM
    t1,
    t2
WHERE
        t1.header_id = t2.header_id
    AND abs(t1.net_amt) = abs(t2.net_amt)
UNION ALL
SELECT
    t2.entity,
    t2.header_id,
    t2.net_amt,
    t1.entity related_entity
FROM
    t1,
    t2
WHERE
        t1.header_id = t2.header_id
    AND abs(t1.net_amt) = abs(t2.net_amt);

select a.entity_id, a.header_id, a.net_amt, b.entity_id as related_entity
  from xxtb_je_trx a join xxtb_je_trx b on a.header_id = b.header_id and a.net_amt = b.net_amt * -1;