Question

这在SQLite中是否可行？

像：

UNIQUE(col1, col2 = "something", col3),

我的意思是独特的：

#1  col1=Foo | col2=Foo       | col3=Foo   > OK
#2  col1=Foo | col2=Foo       | col3=Foo   > OK
#3  col1=Foo | col2=something | col3=Foo   > OK
#4  col1=Foo | col2=something | col3=Foo   > Should fail because of #3
#5  col1=Foo | col2=something | col3=Bar   > OK
#6  col1=Foo | col2=something | col3=Bar   > Should fail because of #5

Answer 1

不直接支持此功能;你必须用触发器实现它：

CREATE TRIGGER something_unique_check
BEFORE INSERT ON MyTable
FOR EACH ROW
WHEN NEW.col2 = 'something'
BEGIN
    SELECT RAISE(FAIL, '"something" record is not unique')
    FROM MyTable
    WHERE col1 = NEW.col1
      AND col2 = NEW.col2
      AND col3 = NEW.col3;
END;

Answer 2

我没有测试过，但我认为你可以用partial indexes in SQLite 3.8.0（2013-08-26发布）来做到这一点：

CREATE UNIQUE INDEX
    "partial_index" ON "table" ("col1", "col2", "col3")
WHERE ("col2" = 'something');

我可能错了。

Answer 3

我建议使用表级cheque约束

ALTER TABLE T
ADD CONSTRAINT CK_something CHECK (col2 != "something" OR (col1<>col2 AND col1<>col3 AND col2<>col3))

其他选择是使用触发器，但这是一种更复杂的方法。

UNIQUE约束但仅限于column = something

3 个答案: