如何查看sql表的唯一约束条件

要查看SQL表中定义的唯一约束条件，你可以使用以下几种方法：

1. 使用 `INFORMATION_SCHEMA.TABLE_CONSTRAINTS` 和 `INFORMATION_SCHEMA.CONSTRAINT_COLUMN_USAGE` 表

这是最常用的方法，它可以在大多数数据库管理系统（如MySQL、PostgreSQL、SQL Server等）中工作。

MySQL 示例：

```sql

SELECT

tc.CONSTRAINT_NAME,

ccu.COLUMN_NAME

FROM

INFORMATION_SCHEMA.TABLE_CONSTRAINTS AS tc

JOIN

INFORMATION_SCHEMA.CONSTRAINT_COLUMN_USAGE AS ccu

ON

tc.CONSTRAINT_NAME = ccu.CONSTRAINT_NAME

WHERE

tc.TABLE_NAME = 'your_table_name' AND

tc.TABLE_SCHEMA = 'your_database_name' AND

tc.CONSTRAINT_TYPE = 'UNIQUE';

```

PostgreSQL 示例：

```sql

SELECT

tc.constraint_name,

ccu.column_name

FROM

information_schema.table_constraints AS tc

JOIN

information_schema.constraint_column_usage AS ccu

ON

tc.constraint_name = ccu.constraint_name

WHERE

tc.table_name = 'your_table_name' AND

tc.table_schema = 'public' AND

tc.constraint_type = 'UNIQUE';

```

SQL Server 示例：

```sql

SELECT

o.name AS constraint_name,

c.name AS column_name

FROM

sys.tables t

JOIN

sys.indexes i ON t.object_id = i.object_id

JOIN

sys.index_columns ic ON i.object_id = ic.object_id AND i.index_id = ic.index_id

JOIN

sys.columns c ON ic.object_id = c.object_id AND ic.column_id = c.column_id

JOIN

sys.partitions p ON i.object_id = p.object_id AND i.index_id = p.index_id

JOIN

sys.allocation_units au ON p.partition_id = au.container_id

JOIN

sys.objects o ON i.object_id = o.object_id

WHERE

t.name = 'your_table_name' AND

o.type = 'C' AND

i.index_id <= 1 AND

i.is_unique = 1;

```

2. 使用数据库特定命令

某些数据库管理系统提供了特定的命令来查看唯一约束。

SQL Server 示例：

```sql

SELECT

o.name AS constraint_name,

c.name AS column_name

FROM

sys.objects o

JOIN

sys.index_columns ic ON o.object_id = ic.object_id

JOIN

sys.columns c ON ic.object_id = c.object_id AND ic.column_id = c.column_id

JOIN

sys.indexes i ON ic.object_id = i.object_id AND ic.index_id = i.index_id

WHERE

o.type = 'C' AND

i.is_unique = 1 AND

o.name = 'your_table_name';

```

注意：

将 `'your_table_name'` 替换为你要查询的表名。

将 `'your_database_name'` 替换为你的数据库名（对于MySQL）。

对于SQL Server，你需要替换 `'public'` 为你的schema名称。

以上命令适用于大多数数据库系统，但具体的SQL语法可能因数据库而异。