从补丁 198 开始，Amazon Redshift 将不再支持创建新的 Python UDF。现有的 Python UDF 将继续正常运行至 2026 年 6 月 30 日。有关更多信息，请参阅[博客文章](https://aws.amazon.com/blogs/big-data/amazon-redshift-python-user-defined-functions-will-reach-end-of-support-after-june-30-2026/)。

# SHOW CONSTRAINTS
<a name="r_SHOW_CONSTRAINTS"></a>

显示表中主键和外键约束的列表。

## 所需的权限
<a name="r_SHOW_CONSTRAINTS-required-permissions"></a>

要对表执行 SHOW CONSTRAINTS，当前用户必须满足下列条件之一：
+ 是超级用户
+ 是该表的拥有者
+ 已被授予父架构的 USAGE 权限以及表的 SELECT 权限

## 语法
<a name="r_SHOW_CONSTRAINTS-synopsis"></a>

```
SHOW CONSTRAINTS {PRIMARY KEYS | FOREIGN KEYS [EXPORTED]}
FROM TABLE
{ database_name.schema_name.table_name | schema_name.table_name }
[LIMIT row_limit]
```

## 参数
<a name="r_SHOW_CONSTRAINTS-parameters"></a>

*database\$1name*  
包含目标表的数据库的名称

*schema\$1name*  
包含目标表的架构的名称

*table\$1name*  
目标表的名称

EXPORTED  
如果指定 EXPORTED，则列出其他表中所有引用目标表的外键。

*row\$1limit*  
要返回的最大行数。*row\$1limit* 可以是 0–10000。

## 示例
<a name="r_SHOW_CONSTRAINTS-examples"></a>

以下示例显示表 demo\$1db.demo\$1schema.pk1 中的主键约束：

```
SHOW CONSTRAINTS PRIMARY KEYS FROM TABLE demo_db.demo_schema.pk1;
 database_name | schema_name | table_name | pk_name  | column_name | key_seq 
---------------+-------------+------------+----------+-------------+---------
 demo_db       | demo_schema | pk1        | pk1_pkey | i           |       1
 demo_db       | demo_schema | pk1        | pk1_pkey | j           |       2
 demo_db       | demo_schema | pk1        | pk1_pkey | c           |       3
```

以下示例显示表 demo\$1schema.fk2 中的外键约束：

```
SHOW CONSTRAINTS FOREIGN KEYS FROM TABLE demo_schema.fk2;
 pk_database_name | pk_schema_name | pk_table_name | pk_column_name | fk_database_name | fk_schema_name | fk_table_name | fk_column_name | key_seq |  fk_name   | pk_name  | update_rule | delete_rule | deferrability 
------------------+----------------+---------------+----------------+------------------+----------------+---------------+----------------+---------+------------+----------+-------------+-------------+---------------
 demo_db          | demo_schema    | pk1           | i              | demo_db          | demo_schema    | fk2           | i              |       1 | fk2_i_fkey | pk1_pkey |             |             | 
 demo_db          | demo_schema    | pk1           | j              | demo_db          | demo_schema    | fk2           | j              |       2 | fk2_i_fkey | pk1_pkey |             |             | 
 demo_db          | demo_schema    | pk1           | c              | demo_db          | demo_schema    | fk2           | c              |       3 | fk2_i_fkey | pk1_pkey |             |             |
```

以下示例显示表 demo\$1schema.pk1 中导出的外键约束：

```
SHOW CONSTRAINTS FOREIGN KEYS EXPORTED FROM TABLE demo_schema.pk1;
 pk_database_name | pk_schema_name | pk_table_name | pk_column_name | fk_database_name | fk_schema_name | fk_table_name | fk_column_name | key_seq |     fk_name     | pk_name  | update_rule | delete_rule | deferrability 
------------------+----------------+---------------+----------------+------------------+----------------+---------------+----------------+---------+-----------------+----------+-------------+-------------+---------------
 demo_db          | demo_schema    | pk1           | i              | demo_db          | demo_schema    | fk2           | i              |       1 | fk2_i_fkey      | pk1_pkey |             |             | 
 demo_db          | demo_schema    | pk1           | j              | demo_db          | demo_schema    | fk2           | j              |       2 | fk2_i_fkey      | pk1_pkey |             |             | 
 demo_db          | demo_schema    | pk1           | c              | demo_db          | demo_schema    | fk2           | c              |       3 | fk2_i_fkey      | pk1_pkey |             |             | 
 demo_db          | demo_schema    | pk1           | i              | demo_db          | demo_schema    | other_fk      | i              |       1 | other_fk_i_fkey | pk1_pkey |             |             | 
 demo_db          | demo_schema    | pk1           | j              | demo_db          | demo_schema    | other_fk      | j              |       2 | other_fk_i_fkey | pk1_pkey |             |             | 
 demo_db          | demo_schema    | pk1           | c              | demo_db          | demo_schema    | other_fk      | c              |       3 | other_fk_i_fkey | pk1_pkey |             |             |
```