是否可以制作XOR CHECK CONSTRAINT?
我在我刚刚制作的测试表上做了这个名为测试并且有3列:
我为此做了一个检查约束:
(a IS NOT NULL AND b = NULL) OR (b IS NOT NULL AND a = NULL)
Which apparently would work in MSSQL
我通过这样做测试了它:
INSERT INTO public.test(
id, a, b)
VALUES (1, 1, 1);
哪个应该失败,因为它在OR的任何一侧都没有评估为TRUE。 但是,插入就好了。
当我看到postgres实际存储为约束时,我得到了这个:
(a IS NOT NULL AND b = NULL::bigint OR b IS NOT NULL AND a = NULL::bigint)
我听说AND先于OR,所以即使这样也应该有效。
有人有解决方案吗?优选地,也可以具有三列或更多列?我知道那些可能会更复杂。
编辑:改变
= NULL
到
IS NULL
告诉我:
ERROR: cannot cast type boolean to bigint
答案 0 :(得分:12)
是的,b = NULL
和OR
位是@a_horse_with_no_name指示的问题。您也可以考虑这种衍生物,它不需要create table test
(
id integer primary key,
a integer,
b integer,
check ((a IS NULL) != (b IS NULL))
);
运算符:
XOR
当然,这仅适用于两列XOR
比较。在类似的测试表中进行三个或更多列create table test
(
id integer primary key,
a integer,
b integer,
c integer,
check ((a IS NULL)::INTEGER +
(b IS NULL)::INTEGER +
(c IS NULL)::INTEGER = 1)
);
比较,您可以采用类似的方法:
db.collection.update({
"_id" : ObjectId("5890c87051e301f17d9ba814"),
"comments.5890db366a29d63612e1f8f5":{$exists:true}
},{
$push:{
"comments.$.array":rateReviewObject.comment
}
})
答案 1 :(得分:6)
您无法将NULL值与=
进行比较,需要IS NULL
(a IS NOT NULL AND b is NULL) OR (b IS NOT NULL AND a is NULL)
对于检查约束,您需要将整个表达式括在括号中:
create table xor_test
(
id integer primary key,
a integer,
b integer,
check ((a IS NOT NULL AND b is NULL) OR (b IS NOT NULL AND a is NULL))
);
-- works
INSERT INTO xor_test(id, a, b) VALUES (1, null, 1);
-- works
INSERT INTO xor_test(id, a, b) VALUES (2, 1, null);
-- failse
INSERT INTO xor_test(id, a, b) VALUES (3, 1, 1);
答案 2 :(得分:1)
这很明显是“异或”。为什么不先将其定义为布尔运算符?在其他情况下也可能有用。
CREATE OR REPLACE FUNCTION public.xor (a boolean, b boolean) returns boolean immutable language sql AS
$$
SELECT (a and not b) or (b and not a);
$$;
CREATE OPERATOR #
(
PROCEDURE = public.xor,
LEFTARG = boolean,
RIGHTARG = boolean
);
然后检查((a IS NULL) # (b IS NULL))
答案 3 :(得分:1)
感谢维克。我也有类似的测试。左连接中至少有2列或更多列不能为空。
SELECT
(tbl1.col1 IS NOT NULL)::INTEGER +
(tbl2.col1 IS NOT NULL)::INTEGER +
(tbl3.col1 IS NOT NULL)::INTEGER +
(tbl4.col1 IS NOT NULL)::INTEGER +
(tbl5.col1 IS NOT NULL)::INTEGER +
(tbl6.col1 IS NOT NULL)::INTEGER > 1 AS
b_mult_cols
FROM tlb1
LEFT JOIN tbl2 ON tlb1.col1 = tlb2.col1
LEFT JOIN tbl3 ON tlb1.col1 = tlb3.col1
LEFT JOIN tbl4 ON tlb1.col1 = tlb4.col1
LEFT JOIN tbl5 ON tlb1.col1 = tlb5.col1
LEFT JOIN tbl6 ON tlb1.col1 = tlb6.col1