MYSQL 限制左连接查询

Question

我有一个查询，它使用一些左连接来取回数据。困境是我想 LIMIT 和 ORDER BY 左连接之一的结果，从而限制带回的总行数。

我尝试订购的 table 限额是 table4

我的查询：

SELECT SQL_CALC_FOUND_ROWS e.meta_1, a.requestid, b.clientid, c.job_description, d.forename
FROM quotations_request AS a 

 LEFT JOIN table1 AS b ON (a.assigned_to = b.userid) 
 LEFT JOIN table2 AS c ON (a.job_costing = c.jobid) 
 LEFT JOIN table3 AS d ON (a.clientid = d.clientid) 
 LEFT JOIN table4 AS e ON (e.quotationid = a.requestid)

 WHERE a.archived = '0' AND (e.meta_1 = LCASE('requested') )

我试过的：

SELECT SQL_CALC_FOUND_ROWS statuss.meta_1, a.requestid, b.clientid, c.job_description, d.forename,
 FROM quotations_request AS a 

 LEFT JOIN table1 AS b ON (a.assigned_to = b.userid) 
 LEFT JOIN table2 AS c ON (a.job_costing = c.jobid) 
 LEFT JOIN table3 AS d ON (a.clientid = d.clientid) 
 LEFT JOIN (Select meta_1 from table4 where quotationid = a.requestid ORDER BY uploaded_date DESC LIMIT 0, 1) 
 as statuss ON (statuss.quotationid = a.requestid)

 WHERE a.archived = '0' AND (statuss.meta_1 = LCASE('requested') )

结果：

在尝试上面的方法后我得到一个错误提示 a.requestid is unknown in the where clause (for the last left join)

Answer 1

试试这个：

SELECT SQL_CALC_FOUND_ROWS statuss.meta_1, a.requestid, b.clientid, c.job_description, d.forename
 FROM quotations_request AS a 

 LEFT JOIN table1 AS b ON (a.assigned_to = b.userid) 
 LEFT JOIN table2 AS c ON (a.job_costing = c.jobid) 
 LEFT JOIN table3 AS d ON (a.clientid = d.clientid) 
 LEFT JOIN (
    select *
    from (select
            t.*,
            @rn := if(quotationid = @qid, @rn + 1, 
                if(@qid := quotationid, 1, 1)
            ) rn
        from (
        select *
        from table4
        order by quotationid, uploaded_date desc) t cross join (
            select @rn := 0, @qid := -1
        ) t2
    ) t where rn = 1
) 
 as statuss ON (statuss.quotationid = a.requestid)

 WHERE a.archived = '0' AND (statuss.meta_1 = LCASE('requested') )

用户变量@rn 和@qid 用于从最新的uploaded_date 表4 中查找前1 行，然后将其与其他表

连接

MYSQL 限制左连接查询

MYSQL Limiting left join query

mysql

sql-order-by

left-join

limit