SQL查詢性能調優

Question

UPDATE nas_backup
SET fiber_serviceability_class = '0', 
last_updated_ts = CURRENT_TIMESTAMP 
WHERE location_id IN ( 
SELECT location_id 
FROM ( 
WITH distinct_locs AS ( 
    SELECT location_id, boundary_type 
    FROM ( 
        SELECT location_id, boundary_type 
        FROM nc
        WHERE technology_type = 'Fibre' 
    ) 
    GROUP BY location_id, boundary_type 
    HAVING COUNT( * ) = 1
)
SELECT nas.location_id
FROM distinct_locs, nas_backup nas
WHERE distinct_locs.location_id = nas.location_id
AND distinct_locs.boundary_type = 'FSA'
GROUP BY nas.location_id
)
);

任何人都可以提出一種優化查詢的方法。 現在需要超過5分鍾。

表nc有1600萬條記錄，表nas_backup有200萬條記錄。

Answer 1

EXISTS可以幫助您一點。 試試看：

UPDATE nas_backup
SET fiber_serviceability_class = '0', 
last_updated_ts = CURRENT_TIMESTAMP 
-- Remove the IN condition and check only that at least one row exists
WHERE EXISTS ( 
SELECT location_id 
FROM ( 
    WITH distinct_locs AS ( 
        SELECT location_id, boundary_type 
        FROM ( 
            SELECT location_id, boundary_type 
            FROM nc
            WHERE technology_type = 'Fibre'
        ) 
        GROUP BY location_id, boundary_type 
        HAVING COUNT( * ) = 1
    )
    SELECT
        nas.location_id
    FROM
        distinct_locs
    WHERE
        distinct_locs.boundary_type = 'FSA'
        -- This is the new line
        AND distinct_locs.location_id = nas_backup.location_id
    GROUP BY
        nas.location_id
    )
);

但是，如果您與我們分享數據庫的結構和目標，將會更容易獲得幫助。

下次，請與我們分享您正在使用的DBMS的供應商和版本。

Answer 2

無論如何，我在這里所說的大多數事情都應該由一個好的優化程序來完成，所以這主要是出於更好的可讀性的原因。

您已將所有過濾器應用於位置部分，因此將其帶到子查詢以減少結果集：

SELECT location_id, boundary_type 
FROM nc 
WHERE technology_type = 'Fibre' AND nc.boundary_type='FSA'
GROUP BY location_id, boundary_type 
HAVING COUNT(*) = 1

接下來，使用JOIN語法而不是隱式Join：

UPDATE nas fiber_serviceability_class = '0', last_updated_ts = CURRENT_TIMESTAMP 
FROM nas_backup nas
    JOIN (SELECT location_id, boundary_type 
            FROM nc 
            WHERE technology_type = 'Fibre' AND nc.boundary_type='FSA'
            GROUP BY location_id, boundary_type 
            HAVING COUNT(*) = 1) loc ON loc.location_id=nas.location_id

我不知道帶有HAVING子句的子查詢是否有特殊原因。 不知道您的結構和數據只是一個猜測，但也許您不需要。 這是一個非常簡單的查詢，然后轉換為“同時更新每個nas_backup，其中技術類型為Fiber，邊界類型為FSA”。

UPDATE nas fiber_serviceability_class = '0', last_updated_ts = CURRENT_TIMESTAMP 
FROM nas_backup nas
    JOIN nc ON nas.location_id=nc.location_id
WHERE nc.technology_type='Fibre'
    AND nc.boundary_type='FSA'