如果没有外部引用则删除行，否则更新

Question

我有一个包含三个表的DB2数据库：locations，items，movement_history。 items表的外键location_id为locations。 movement_history表在[{1}}中有一个外键item_id，在items中有两个外键location_id_before和location_id_after。< / p>

如果locations或location中没有行引用，我想删除items。如果在某处引用了movement_history行 ，我只想更新它以标记为已删除。有没有办法在一个声明中这样做？最好的方法是什么？

Answer 1

尝试这样的命令：

MERGE INTO LOCATIONS AS LOC
USING (
  SELECT Q1.ID, COALESCE(Q4.LOCATION_AFTER, Q3.LOCATION_BEFORE, Q2.LOCATION) AS ANY_REF
  FROM LOCATIONS Q1
    LEFT OUTER JOIN ITEMS Q2 ON Q2.LOCATION = Q1.ID
    LEFT OUTER JOIN MOVEMENT_HISTORY Q3 ON Q3.LOCATION_BEFORE = Q1.ID
    LEFT OUTER JOIN MOVEMENT_HISTORY Q4 ON Q4.LOCATION_AFTER = Q1.ID) AS T1
    ON LOC.ID = T1.ID
WHEN MATCHED AND T1.ANY_REF IS NOT NULL THEN
  UPDATE SET ACTUAL = 'N'
WHEN MATCHED AND T1.ANY_REF IS NULL THEN
  DELETE