在sql中加入四个以上的表

Question

我有以下包含以下列的表格： http ://sqlfiddle.com/#!2/ 8776a0 /2 中的更多信息

request : {id,request_id, client_id, product_name, designation_date_1, can }
assigned_samples:{id,labref, user_id, stat}
users{id, fname, lname}
clients:{id, name}
tracking_table{labref, activity, added_date}

我想要做的是加入所有这些表，并在加入跟踪表时提出一个包含所有数据的大表，条件是检查活动列是否给出了像“a”这样的值，如果没有匹配的行找到了，date_ added 应该是空的，否则显示 date_ added

result table {labref, prod, desc_date, can, CONCAT(fname,' ',lname), date_added}

SELECT r.request_id, r.product_name, r.can, r.designation_date_1, CONCAT(u.fname,' ', u.lname) as analyst, a_s.stat
FROM request r, assigned_samples a_s, user u, clients c
WHERE r.client_id=c.id
AND a_s.analyst_id = u.id
AND r.request_id = a_s.labref
AND r.client_id='2'
GROUP BY r.request_id

如果我向查询添加条件，它会返回数据，但 date_ added 是完全相同的，这是错误的

SELECT r.request_id, r.product_name, r.can, r.designation_date_1, CONCAT(u.fname,' ', u.lname) as analyst, a_s.stat
FROM request r, assigned_samples a_s, user u, clients c, tracking_table t
WHERE r.client_id=c.id
AND a_s.analyst_id = u.id
AND r.request_id = a_s.labref
AND t.activity ='Authorizing COA Release'
AND r.client_id='2'
GROUP BY r.request_id

Answer 1

应为tracking_table添加join condition 。

尝试这个：

SQLFiddle： http ://sqlfiddle.com/#!2/3a116f/1

（我稍微改变了演示的输入数据）

SELECT r.request_id, r.product_name, r.can, r.designation_date_1, CONCAT(u.fname,' ', u.lname) as analyst, a_s.stat,
  date_added
FROM request r, assigned_samples a_s, user u, clients c, tracking_table t
WHERE r.client_id=c.id
AND a_s.analyst_id = u.id
AND r.request_id = a_s.labref
AND r.client_id='2'
AND r.request_id = t.labref
AND t.activity ='Authorizing COA Release'