如何優化DELETE .. NOT IN .. SUBQUERY在火鳥

Question

我這種刪除查詢：

DELETE 
FROM SLAVE_TABLE 
WHERE ITEM_ID NOT IN (SELECT ITEM_ID FROM MASTER_TABLE) 

還有什麼辦法來優化呢？

Answer 1

您可以使用EXECUTE BLOCK順序掃描詳細表並刪除沒有主記錄匹配的記錄。

EXECUTE BLOCK 
AS 
    DECLARE VARIABLE C CURSOR FOR 
    (SELECT d.id 
    FROM detail d LEFT JOIN master m 
     ON d.master_id = m.id 
    WHERE m.id IS NULL); 
    DECLARE VARIABLE I INTEGER; 
BEGIN 
    OPEN C; 
    WHILE (1 = 1) DO 
    BEGIN 
    FETCH C INTO :I; 
    IF(ROW_COUNT = 0)THEN 
     LEAVE; 
    DELETE FROM detail WHERE id = :I; 
    END 
    CLOSE C; 
END 

Answer 2

(NOT) IN通常可以通過使用(NOT) EXISTS來代替優化。

DELETE 
FROM SLAVE_TABLE 
WHERE NOT EXISTS (SELECT 1 FROM MASTER_TABLE M WHERE M.ITEM_ID = ITEM_ID) 

我不知道你正在嘗試做的，但對我這個查詢表明您應該使用外鍵來執行這些類型的限制，無法運行查詢，清理殘局之後。