mysql中查询语句： 我有三个数据表clrk，clrkmx，ffcl三个数据库表：联合查询

select a.dwmc,a.wzmc,a.ggxh,a.jldw,a.mldj,a.sssl,b.srfs,b.srsl,gh=(select sum(fcsl) group by gh),fcsl=(select sum(srsl) group by srfs)

from clrk as a

left join clrkmx as b on a.dwmc=b.dwmc and a.ggxh=b.ggxh and wzmc=wzmc//要有主外键关系，尽量写主外键的

left join ffcl as c on a.wzmc=c.wzmc and a.ggxh=c.ggxh

where ?.cgrq=传条件//抓狂，这个字段，三个表里都没有啊，还是没标出来，标出来的话，问号就是那个表

select sum(srsl) group by srfs

如果数据库是远程的话可以直接在工程中连接数据库

public static class database

{

//数据库链接

static MySqlConnection Conn = null

//连接数据库

static void OpenConn()

{

if (Conn != null &&Conn.State == ConnectionState.Open)

{

Conn.Close()

}

if (Conn == null)

{

Conn = new MySqlConnection(你的数据库连接字符串)

}

if (Conn.State == ConnectionState.Closed)

{

Conn.Open()

}

}

//关闭数据库连接

static void CloseConn()

{

if (Conn != null)

{

Conn.Close()

}

}

//执行SQL语句

public static bool ExecSql(string strSql)

{

try

{

OpenConn()

MySqlCommand Cmd = new MySqlCommand(strSql, Conn)

Cmd.ExecuteNonQuery()

Cmd.Dispose()

return true

}

catch (Exception ex)

{

return false

}

finally

{

CloseConn()

}

}

//获取DataSet接口

public static DataSet GetDataSet(string strSql, string strDataSetName)

{

try

{

OpenConn()

DataSet dataSet = new DataSet()

MySqlDataAdapter dataAdapter = new MySqlDataAdapter(strSql, Conn)

dataAdapter.Fill(dataSet, strDataSetName)

dataAdapter.Dispose()

return dataSet

}

catch(Exception ex)

{

return null

}

finally

{

CloseConn()

}

}

//获取MySqlDataReader接口

public static MySqlDataReader GetDataReader(string strSql)

{

try

{

OpenConn()

MySqlCommand Cmd = new MySqlCommand(strSql, Conn)

MySqlDataReader dataReader = Cmd.ExecuteReader()

return dataReader

}

catch (Exception ex)

{

return null

}

}

}

要去网上下一个MySql.Data.dll 然后倒入就可以使用上面的代码连接数据库了

SELECT tableAlias.fields FROM table AS Alias LEFT JOIN table1 AS Alias1 ON conditions LEFT JOIN table2 AS Alias2 ON conditions

按照这个模式写出来就OK了

你的问题描述的不是很清楚，我也只能是给你一个模式了！

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