C# WPF SQL SELECT 内连接

Question

我正在尝试加入用户表以检索用户登录名。 我希望有两个 INNER 连接，一个用于 CreatedByUser_loginname 和 ModifiedByUser_loginname

但目前我只是想获得正确的 SQL 查询字符串语法。 但是，当我使用 AS“名称”更改 INNER JOIN 的名称时，执行 sqlreader() 方法时会抛出异常。如果我删除 AS ...它可以工作，但是我无法将第二个 INNER JOIN 添加到同一个用户表中以获取修改后的用户登录名的名称。

这是有问题的代码

这不起作用

String sqlComStr = "SELECT Company_ID, Company_Name, Company_Address1, Company_Address2, Company_Address3, Company_Suburb, Company_City, " +
    "Company_State, Company_PostCode, Company_Phone, Company_Fax, Company_WebsiteUrl, Company_Status, Company_ModifiedByUser_ID, Company_CreatedByUser_ID, " +
    " [U1].User_LoginName " +
    "FROM Company INNER JOIN [User] AS U1 ON [User].User_ID = [Company].Company_CreatedByUser_ID WHERE [Company].isDeleted = 0" + companyFilter;

这确实

String sqlComStr = "SELECT Company_ID, Company_Name, Company_Address1, Company_Address2, Company_Address3, Company_Suburb, Company_City, " +
    "Company_State, Company_PostCode, Company_Phone, Company_Fax, Company_WebsiteUrl, Company_Status, Company_ModifiedByUser_ID, Company_CreatedByUser_ID, " +
    " User_LoginName " +
    "FROM Company INNER JOIN [User] ON [User].User_ID = [Company].Company_CreatedByUser_ID WHERE [Company].isDeleted = 0" + companyFilter;

......

String sqlComStr = "SELECT Company_ID, Company_Name, Company_Address1,    Company_Address2, Company_Address3, Company_Suburb, Company_City, " +
    "Company_State, Company_PostCode, Company_Phone, Company_Fax, Company_WebsiteUrl, Company_Status, Company_ModifiedByUser_ID, Company_CreatedByUser_ID, " +
    " [U1].User_LoginName " +
    "FROM Company INNER JOIN [User] AS U1 ON [User].User_ID = [Company].Company_CreatedByUser_ID WHERE [Company].isDeleted = 0" + companyFilter;

sqlcmd.CommandText = sqlComStr;
sqlCon.ConnectionString = "Data Source='PTSSHM\\SQLEXPRESS'; Initial Catalog='PROACTIVE'; Integrated Security=True;";
//sqlCon.ConnectionString = App.appSqlConnectionString;
sqlcmd.Connection = sqlCon;

try
{
    sqlCon.Open();

    SqlDataReader sqlReader = sqlcmd.ExecuteReader(CommandBehavior.Default);
    // If no Exception thrown at this point clear the quote items
    companys.Clear();

    while (sqlReader.Read())
    // Read each row and create a new quite item object int he quoteitems list
    {
        companys.Add(new Company((int)sqlReader["Company_ID"],
            (string)sqlReader["Company_Name"].ToString(),
            (string)sqlReader["Company_Address1"].ToString(),
            (string)sqlReader["Company_Address2"].ToString(), 
            (string)sqlReader["Company_Address3"].ToString(),
            (string)sqlReader["Company_Suburb"].ToString(),
            (string)sqlReader["Company_City"].ToString(),
            (string)sqlReader["Company_State"].ToString(),       
            (string)sqlReader["Company_PostCode"].ToString(),
            (string)sqlReader["Company_Phone"].ToString(),
            (string)sqlReader["Company_Fax"].ToString(),
            (string)sqlReader["Company_WebsiteUrl"].ToString(),
            (string)sqlReader["Company_Status"].ToString(),
            (int)sqlReader["Company_ModifiedByUser_ID"],
            (int)sqlReader["Company_CreatedByUser_ID"],
            (string)sqlReader["[U1].User_LoginName"].ToString(), "d"));
    }
}

Answer 1

如果您使用表名的别名（例如 User 作为 U1），则查询中不再存在名称 [user]，您必须在对其的所有后续引用中使用 U1。

INNER JOIN [User] AS U1 ON [User].User_ID = [Company].Company_CreatedByUser_ID

您仍在连接子句中使用 User，

INNER JOIN [User] AS U1 ON U1.User_ID = [Company].Company_CreatedByUser_ID

Answer 2

固定

String sqlComStr = "SELECT Company_ID, Company_Name, Company_Address1, Company_Address2, Company_Address3, Company_Suburb, Company_City, " +
            "Company_State, Company_PostCode, Company_Phone, Company_Fax, Company_WebsiteUrl, Company_Status, Company_ModifiedByUser_ID, Company_CreatedByUser_ID, " +
            " [CreateUser].User_LoginName AS CreateUser, [ModUser].User_LoginName AS ModUser  " +
            "FROM Company INNER JOIN [User] As [CreateUser] ON [CreateUser].User_ID = [Company].Company_CreatedByUser_ID INNER JOIN [User] AS [ModUser] ON [ModUser].User_ID = [Company].Company_ModifiedByUser_ID WHERE [Company].isDeleted = 0" + companyFilter;

和

companys.Add(new Company((int)sqlReader["Company_ID"], (string)sqlReader["Company_Name"].ToString(), (string)sqlReader["Company_Address1"].ToString(),
                    (string)sqlReader["Company_Address2"].ToString(), (string)sqlReader["Company_Address3"].ToString(), (string)sqlReader["Company_Suburb"].ToString(),
                    (string)sqlReader["Company_City"].ToString(), (string)sqlReader["Company_State"].ToString(), (string)sqlReader["Company_PostCode"].ToString(),
                    (string)sqlReader["Company_Phone"].ToString(), (string)sqlReader["Company_Fax"].ToString(), (string)sqlReader["Company_WebsiteUrl"].ToString(),
                    (string)sqlReader["Company_Status"].ToString(), (int)sqlReader["Company_ModifiedByUser_ID"], (int)sqlReader["Company_CreatedByUser_ID"],
                    (string)sqlReader["CreateUser"].ToString(), (string)sqlReader["ModUser"].ToString()));