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。到目前为止，这是我尝试过的:

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，但出于某种原因，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