c# - 如何获取表和主键，如果表没有主键则显示null？

Question

我目前正在尝试通过在 C# 中调用以下 SQL 来检索每个表的表名和主键。这是我迄今为止尝试过的：

SELECT t.TABLE_NAME As 'Table Name',
       Keys.COLUMN_NAME AS 'Primary Key'
FROM INFORMATION_SCHEMA.TABLES t 
left outer join INFORMATION_SCHEMA.TABLE_CONSTRAINTS Constraints
         on  t.TABLE_NAME = Constraints.Table_name 
         and t.Table_Schema = Constraints.Table_Schema 
left outer join INFORMATION_SCHEMA.KEY_COLUMN_USAGE AS Keys 
         ON  Constraints.TABLE_NAME = Keys.TABLE_NAME 
         and Constraints.CONSTRAINT_NAME = Keys.CONSTRAINT_NAME 
         and Constraints.CONSTRAINT_TYPE = 'PRIMARY KEY'

问题是如果表没有主键，我希望结果只包含一个“空”条目。虽然它正在工作，但由于某种原因，结果包含“薪水”表的副本，如下所示。Salary 和Employees 表都有主键，而“Test”表没有：

编辑：我现在已经尝试过了，它似乎有效。这样做有什么缺点吗？

SELECT T.TABLE_NAME As 'Table Name'
    ,       (
            Select K1.COLUMN_NAME
            From INFORMATION_SCHEMA.TABLE_CONSTRAINTS As C1
                Join INFORMATION_SCHEMA.KEY_COLUMN_USAGE As K1
                    On C1.TABLE_SCHEMA = K1.TABLE_SCHEMA
                        And C1.TABLE_NAME = K1.TABLE_NAME 
                        And C1.CONSTRAINT_NAME = K1.CONSTRAINT_NAME 
            Where C1.CONSTRAINT_TYPE = 'PRIMARY KEY'
                And T.TABLE_SCHEMA = C1.TABLE_SCHEMA 
                And T.TABLE_NAME = C1.TABLE_NAME 
            )As PrimaryKeyColumns
FROM INFORMATION_SCHEMA.TABLES As T 

Answer 1

尝试替换此条件Constraints.CONSTRAINT_TYPE = 'PRIMARY KEY' ：

SELECT t.TABLE_NAME As 'Table Name',
       Keys.COLUMN_NAME AS 'Primary Key'
FROM INFORMATION_SCHEMA.TABLES t 
left outer join INFORMATION_SCHEMA.TABLE_CONSTRAINTS Constraints
         on  t.TABLE_NAME = Constraints.Table_name 
         and t.Table_Schema = Constraints.Table_Schema  
         and Constraints.CONSTRAINT_TYPE = 'PRIMARY KEY'       
left outer join INFORMATION_SCHEMA.KEY_COLUMN_USAGE AS Keys 
         ON  Constraints.TABLE_NAME = Keys.TABLE_NAME 
         and Constraints.CONSTRAINT_NAME = Keys.CONSTRAINT_NAME 

Answer 2

您应该考虑您的 PK 有多列。您可以通过更改为子查询来做到这一点：

SELECT T.TABLE_NAME As 'Table Name'
    ,   Stuff(
            (
            Select ', ' + K1.COLUMN_NAME
            From INFORMATION_SCHEMA.TABLE_CONSTRAINTS As C1
                Join INFORMATION_SCHEMA.KEY_COLUMN_USAGE As K1
                    On C1.TABLE_SCHEMA = K1.TABLE_SCHEMA
                        And C1.TABLE_NAME = K1.TABLE_NAME 
                        And C1.CONSTRAINT_NAME = K1.CONSTRAINT_NAME 
            Where C1.CONSTRAINT_TYPE = 'PRIMARY KEY'
                And T.TABLE_SCHEMA = C1.TABLE_SCHEMA 
                And T.TABLE_NAME = C1.TABLE_NAME 
            For Xml Path(''), type
            ).value('.', 'nvarchar(max)')
            , 1, 2, '') As PrimaryKeyColumns
FROM INFORMATION_SCHEMA.TABLES As T 

---

顺便说一句，如果您真的想对 TABLES 视图使用联接，则需要嵌套联接。问题是您有两个外连接，并且外键中的列正在输出中生成行。应该注意的是，与前面提到的子查询方法相比，以下方法的缺点是，如果主键由多列组成，您将获得多行。也就是说，您可以在 SQL Server 中嵌套联接，以便它首先处理内部联接、内部联接，然后处理外部联接：

SELECT T.TABLE_NAME As 'Table Name'
    , Keys.COLUMN_NAME AS 'Primary Key'
FROM INFORMATION_SCHEMA.TABLES As T
    Left Join( INFORMATION_SCHEMA.TABLE_CONSTRAINTS Constraints
        Join INFORMATION_SCHEMA.KEY_COLUMN_USAGE As Keys 
            On  Constraints.TABLE_SCHEMA = Keys.TABLE_SCHEMA 
                And Constraints.TABLE_NAME = Keys.TABLE_NAME 
                And Constraints.CONSTRAINT_NAME = Keys.CONSTRAINT_NAME 
                And Constraints.CONSTRAINT_TYPE = 'PRIMARY KEY' )
        On T.TABLE_SCHEMA = Constraints.TABLE_SCHEMA 
            And T.TABLE_NAME = Constraints.TABLE_NAME 

在此查询中，首先处理和之间的内连接，TABLE_CONSTRAINTS并将KEY_COLUMN_USAGE结果组合在左连接中TABLES查看。

Answer 3

我看到您已经接受了您的答案，但如果有人感兴趣，这是一个纯 C# 答案：

static void Main(string[] args)
{
    Server server = new Server("serverName");
    Database db = server.Databases["DatabaseName"];

    string tableName = "TableName";

    Table table = db.Tables[tableName];

    if (table != null)
    {
        Console.WriteLine("Table:  {0}", tableName);
        if (table.Columns.Count > 0)
        {
            Console.WriteLine("  Primary Key Columns:");
            foreach (Column column in table.Columns)
            {
                if (column.InPrimaryKey)
                {
                    Console.WriteLine(string.Format("    {0}", column.Name));
                }
            }
        }
        else
        {
            Console.WriteLine("  No primary key.", tableName);
        }
    }
    Console.WriteLine("Press ENTER to exit...");
    Console.ReadLine();
}

您将需要添加对 Microsoft.SqlServer.Management.Sdk.Sfc 和 Microsoft.SqlServer.Smo 程序集的引用并导入适当的命名空间。

Answer 4

select
  TABLE_SCHEMA, 
  TABLE_NAME 
from 
  INFORMATION_SCHEMA.TABLES
where 
  objectproperty(object_id(table_name),'TableHasPrimaryKey')=0
ORDER BY 
  TABLE_NAME