检查单个语句中的许多值不相等

Question

我在表中创建一个约束，以便 8 列中没有一列必须彼此相等。

我想这样做：

alter table mytable
    add constraint no_duplicate_values
        check (col_1 <> col_2 <> col__3 <> col__4 <> col__5 <> col__6 <> col__7 <> col__8);

但是这当然行不通，因为

<>

只接受两个操作数，左和右。

是否有一个优雅的、等效的单语句替代方案？

Answer 1

为此，您需要使用逻辑 AND 运算符。顺便说一句，据我所知，没有什么优雅的方法。你能试试这个吗：

       CHECK (
        col_1 <> col_2 AND
        col_1 <> col_3 AND
        col_1 <> col_4 AND
        col_1 <> col_5 AND
        col_1 <> col_6 AND
        col_1 <> col_7 AND
        col_1 <> col_8 AND
        col_2 <> col_3 AND
        col_2 <> col_4 AND
        col_2 <> col_5 AND
        col_2 <> col_6 AND
        col_2 <> col_7 AND
        col_2 <> col_8 AND
        col_3 <> col_4 AND
        col_3 <> col_5 AND
        col_3 <> col_6 AND
        col_3 <> col_7 AND
        col_3 <> col_8 AND
        col_4 <> col_5 AND
        col_4 <> col_6 AND
        col_4 <> col_7 AND
        col_4 <> col_8 AND
        col_5 <> col_6 AND
        col_5 <> col_7 AND
        col_5 <> col_8 AND
        col_6 <> col_7 AND
        col_6 <> col_8 AND
        col_7 <> col_8
    )

Answer 2

我建议一个简单的辅助函数

create or replace function row_unique(jr jsonb) returns boolean language sql as 
$$
with t(v) as 
(
 select value from jsonb_each_text(jr) j
)
select count(v) = count(distinct(v)) from t;
$$

然后

alter table mytable add constraint no_duplicate_values
check (row_unique(to_jsonb(mytable)));

演示

但是，正如 Thorsten Kettner 评论的那样，可能值得重新审视您的数据设计。