在 MySQL 中显示表命令的约束？

您可以借助 SHOW 命令显示表上的约束。语法如下 -

show create table yourTableName;

上述命令将显示表 ENGINE 的所有约束。使用它，你甚至可以看到所有的列名和相应的数据类型。

为了理解上面的MySQL语句，让我们首先创建一个表 -

mysql> create table ShowConstraintsDemo
   -> (
   -> BookId int not null,
-> BookName varchar(200) not null,
-> BookAuthor varchar(200) Unique not null,
-> Primary key(BookId,BookName)
-> );
Query OK, 0 rows affected (1.04 sec)

现在您可以应用上述语法来显示表上的约束。查询如下 -

mysql> show create table ShowConstraintsDemo;

以下是显示所有约束的输出 -

+---------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table                | Create Table                                                                                                                                                                                                                            |
+---------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| ShowConstraintsDemo | CREATE TABLE `showconstraintsdemo` ( `BookId` int(11) NOT NULL, `BookName` varchar(200) COLLATE utf8mb4_unicode_ci NOT NULL, `BookAuthor` varchar(200) COLLATE utf8mb4_unicode_ci NOT NULL, PRIMARY KEY (`BookId`,`BookName`), UNIQUE KEY `BookAuthor` (`BookAuthor`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci          |
+---------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.05 sec)

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