Den här frågan bör ge samma resultat, men undviker CASE
-- EXPLAIN ANALYZE
UPDATE table_a a
SET rebuilding_costs = drie.rebuilding_costs
FROM (
SELECT COALESCE(b.address, c.address, d.address) AS address
, COALESCE(b.rebuilding_costs, c.rebuilding_costs, d.rebuilding_costs)
AS rebuilding_costs
FROM table_b b
FULL OUTER JOIN table_c c ON c.address = b.address
AND c.rebuilding_costs BETWEEN 200001 AND 400000
FULL OUTER JOIN table_D d ON d.address = b.address
AND d.rebuilding_costs BETWEEN 400001 AND 600000
WHERE b.rebuilding_costs BETWEEN 100001 AND 200000
) drie
WHERE a.address = drie.address
AND a.rebuilding_costs <> drie.rebuilding_costs -- Avoid useless updates
;
UPPDATERING:Ett liknande tillvägagångssätt, baserat på en kedjad uppsättning CTE:er:
-- --------------------------------
EXPLAIN ANALYZE
WITH cte_b AS (
SELECT b.address, b.rebuilding_costs
FROM table_b b
WHERE b.rebuilding_costs BETWEEN 100001 AND 200000
)
, cte_c AS (
SELECT c.address , c.rebuilding_costs
FROM table_c c
WHERE c.rebuilding_costs BETWEEN 200001 AND 400000
AND NOT EXISTS (SELECT * FROM cte_b WHERE cte_b.address = c.address)
)
, cte_d AS (
SELECT d.address , d.rebuilding_costs
FROM table_d d
WHERE d.rebuilding_costs BETWEEN 400001 AND 600000
AND NOT EXISTS (SELECT * FROM cte_b WHERE cte_b.address = d.address)
AND NOT EXISTS (SELECT * FROM cte_c WHERE cte_c.address = d.address)
)
, cte_bcd AS (
SELECT cte_b.address, cte_b.rebuilding_costs FROM cte_b
UNION ALL SELECT cte_c.address, cte_c.rebuilding_costs FROM cte_c
UNION ALL SELECT cte_d.address, cte_d.rebuilding_costs FROM cte_d
)
UPDATE table_a a
SET rebuilding_costs = cte_bcd.rebuilding_costs
FROM cte_bcd
WHERE a.address = cte_bcd.address
-- avoid useless updates this way:
AND a.rebuilding_costs <> cte_bcd.rebuilding_costs
-- ,or this way:
-- AND cte_bcd.rebuilding_costs IS DISTINCT FROM a.rebuilding_costs
;
UPPDATERING 2:CTE:er kan vara långsamma, eftersom de fungerar som optimeringsbarriärer. Ett snabbt och smutsigt sätt är att skriva om dem som (tillfälliga) VIEWS, och hänvisa till dessa istället. Detta gör att optimeraren kan blanda de olika delarna av frågan in i och ut från underfrågor och till och med kombinera och återanvända dessa.
CREATE TEMP VIEW cte_b AS (
SELECT b.address, b.rebuilding_costs
FROM table_b b
WHERE b.rebuilding_costs BETWEEN 100001 AND 200000
);
CREATE TEMP VIEW cte_c AS (
SELECT c.address , c.rebuilding_costs
FROM table_c c
WHERE c.rebuilding_costs BETWEEN 200001 AND 400000
AND NOT EXISTS (SELECT * FROM cte_b WHERE cte_b.address = c.address)
);
CREATE TEMP VIEW cte_d AS (
SELECT d.address , d.rebuilding_costs
FROM table_d d
WHERE d.rebuilding_costs BETWEEN 400001 AND 600000
AND NOT EXISTS (SELECT * FROM cte_b WHERE cte_b.address = d.address)
AND NOT EXISTS (SELECT * FROM cte_c WHERE cte_c.address = d.address)
);
CREATE TEMP VIEW cte_bcd AS (
SELECT cte_b.address, cte_b.rebuilding_costs FROM cte_b
UNION ALL SELECT cte_c.address, cte_c.rebuilding_costs FROM cte_c
UNION ALL SELECT cte_d.address, cte_d.rebuilding_costs FROM cte_d
);
EXPLAIN -- ANALYZE
UPDATE table_a a
SET rebuilding_costs = cte_bcd.rebuilding_costs
FROM cte_bcd
WHERE a.address = cte_bcd.address
AND a.rebuilding_costs <> cte_bcd.rebuilding_costs -- avoid useless updates
-- AND a.address < 100000
;