sql查詢刪除子表中未使用的父表行

Question

我的問題標題正好說我想要幫助。

表定義和關系：

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我在下面的查詢中嘗試了此操作，但未從Measurement_units表中刪除數據“ jl”。 我想在“ measuring_units”表中用62刪除該行，因為“ food_units_relation”表中未使用該行

我嘗試過的一個

DELETE  t2
        FROM food_units_relation t1 JOIN measureing_units t2
        ON t1.measuring_unit_id = t2.measuremnt_id
        WHERE t1.foodUnit_relation_Id = 17 and  t2.measuremnt_id NOT IN(t1.measuring_unit_id) and t2.creater_id=1;

Answer 1

DELETE  t2
FROM measureing_units t2
LEFT JOIN food_units_relation t1 ON t1.measuring_unit_id = t2.measuremnt_id
WHERE t1.foodUnit_relation_Id = 17 and t1.measuring_unit_id is null and t2.creater_id = 1;

Answer 2

DELETE MEASUREING_UNITS.*
FROM MEASUREING_UNITS
  LEFT JOIN FOOD_UNITS_RELATION ON MEASUREING_UNITS.MEASUREMENT_ID = FOOD_UNITS_RELATION.MEASURING_UNIT_ID
WHERE FOOD_UNITS_RELATION.FOOD_UNITS_RELATION_ID IS NULL;

在SQLFiddle上檢查一下。

Answer 3

這里的問題-你使用INNER JOIN，所以你甚至不選擇measuremnt_id不存在，做food_units_relation 。 而是使用RIGHT JOIN並排除t1表的WHERE條件：

DELETE  t2
        FROM food_units_relation t1 RIGHT JOIN measureing_units t2
        ON t1.measuring_unit_id = t2.measuremnt_id
        WHERE t1.measuring_unit_id IS NULL 
              AND t2.creater_id=1;

或者只使用NOT EXISTS：

   DELETE FROM measureing_units t2 
      WHERE NOT EXISTS (SELECT * FROM food_units_relation t1 
                        WHERE t1.measuring_unit_id = t2.measuremnt_id)
            AND t2.creater_id=1