Tim Truman wrote:
Query:
SELECT count(*) as count FROM
(
SELECT *
FROM transaction t, merchant m
WHERE t.merchant_id = m.id
AND m.id = 198
AND t.transaction_date >= '20050101'
AND t.transaction_date <= '20060925'
AND credit_card_no LIKE '1111%111'
UNION ALL
SELECT *
FROM transaction t, merchant m
WHERE t.merchant_id = m.id
AND m.parent_merchant_id = 198
AND t.transaction_date >= '20050101'
AND t.transaction_date <= '20060925'
AND credit_card_no LIKE '1111%111'
) AS foobar
Actually, I think the best course of action is to rewrite the query to a
faster alternative. What you can try is:
SELECT SUM(count) AS count FROM
(
SELECT count(*) AS count
FROM transaction t, merchant m
WHERE t.merchant_id = m.id
AND m.id = 198
AND t.transaction_date >= '20050101'
AND t.transaction_date <= '20060925'
AND credit_card_no LIKE '1111%111'
UNION ALL
SELECT count(*) AS count
FROM transaction t, merchant m
WHERE t.merchant_id = m.id
AND m.parent_merchant_id = 198
AND t.transaction_date >= '20050101'
AND t.transaction_date <= '20060925'
AND credit_card_no LIKE '1111%111'
) AS foobar;
The next optimization is to merge the 2 subqueries into one. If you
schema is such that m.id can not be the same as m.parent_merchant_id I
think your query can be reduced to:
SELECT count(*) AS count
FROM transaction t, merchant m
WHERE t.merchant_id = m.id
AND
(
m.id = 198
OR
m.parent_merchant_id = 198
)
AND t.transaction_date >= '20050101'
AND t.transaction_date <= '20060925'
AND credit_card_no LIKE '1111%111'
If m.id can be the same as m.parent_merchant_id you need something like:
SELECT SUM(
CASE WHEN m.id = m.parent_merchant_id THEN 2 ELSE 1 END
) AS count
FROM transaction t, merchant m
WHERE t.merchant_id = m.id
AND
(
m.id = 198
OR
m.parent_merchant_id = 198
)
AND t.transaction_date >= '20050101'
AND t.transaction_date <= '20060925'
AND credit_card_no LIKE '1111%111'
Jochem
---------------------------(end of broadcast)---------------------------
TIP 9: In versions below 8.0, the planner will ignore your desire to
choose an index scan if your joining column's datatypes do not
match
