防止在CHARACTER VARYING字段中出现空字符串

问题描述

我正在使用PostgreSQL，并希望阻止某些必需的CHARACTER VARYING(VARCHAR)字段允许输入空字符串.

I am using PostgreSQL and would like to prevent certain required CHARACTER VARYING (VARCHAR) fields from allowing empty string inputs.

这些字段还需要包含唯一值，因此我已经在使用唯一约束；但是，这不会阻止原始的(唯一的)空值.

These fields would also need to contain unique values, so I am already using a unique constraint; however, this does not prevent an original (unique) empty value.

基本示例，其中用户名必须唯一且不能为空

Basic example, where username needs to be unique and not empty

| id | username | password |
+----+----------+----------+
| 1  | User1    | pw1      | #Allowed
| 2  | User2    | pw1      | #Allowed
| 3  | User2    | pw2      | #Already prevented by constraint
| 4  | ''       | pw2      | #Currently allowed, but needs to be prevented

推荐答案

使用检查约束:

CREATE TABLE foobar(
  x TEXT NOT NULL UNIQUE,
  CHECK (x <> '')
);

INSERT INTO foobar(x) VALUES('');

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