SQLite中的条件触发继承

Question

我正在使用SQLite，我正在使用XOR单表继承，我想创建一个触发器，使我能够：

1. 如果表InstructionRefs.id
中已创建RideHeightRefs，请在插入前检查

2. 在插入之前Ckeck在另一个继承的表InstructionRefs.id中不存在StrappingRefs。 我拿了一些oracle PL / SQL代码并更改了它，我想从IF NOT EXISTS (SELECT id...)开始写错了：

   CREATE TRIGGER IF NOT EXISTS insert_instructionRefs_trigger BEFORE INSERT ON InstructionRefs
BEGIN
IF NOT EXISTS (SELECT id FROM RideHeightRefs AS RHR INNER JOIN InstructionRefs IR ON RHR.id = IR.id)
BEGIN
SELECT RAISE(FAIL, '"RideHeightRefs" key is unknown. Insertion in "instructionRefs" is impossible.')
END'
IF NOT EXISTS (SELECT * FROM (SELECT RideHeightRefs FROM StrappingRefs UNION ALL SELECT RideHeightRefs FROM InstructionRefs) T WHERE RideHeightRefs IN (SELECT RideHeightRefs FROM NEW)) BEGIN SELECT RAISE(FAIL, '"RideHeightRefs" key is used in another table. Insertion in "StrappingRefs" is impossible.') END END

如何修改代码以使其与sqlite语法兼容？

Answer 1

要检查基表中的相应行是否存在，只需使用foreign key constraint。

SQLite没有IF语句。要检查某些内容，请在SELECT FAIL中添加WHERE子句，或使用触发器的WHEN子句：

CREATE TRIGGER IF NOT EXISTS insert_instructionRefs_trigger
BEFORE INSERT ON InstructionRefs
WHEN EXISTS (SELECT *
             FROM StrappingRefs
             WHERE id = NEW.id)
BEGIN
  SELECT RAISE(FAIL, '"RideHeightRefs" key is used in another table. Insertion in "StrappingRefs" is impossible.');
END;