查詢使用3表

Question

我試圖選擇機器和kpi的每個人使用的列表。

KPIs 
- id  ('123') 

MACHINE 
- id  ('567') 

KPIDATA 
- key  ('k.123.i.567.a.000') 

KPIDATA行說，機567使用KPI 123。如何在一個查詢中選擇這個？

Answer 1

假設你有相同的格式爲Kpidata key領域，即像k.123.i.567.a.000

此查詢可以幫助

SELECT 
     k.`id`, 
     m.`MACHINE`, 
     kd.`key` 
FROM 
     KPIs as k, 
     MACHINE as m, 
     KPIDATA as kd 
WHERE 
     k.`id` = SUBSTR(kd.`key`,LOCATE('.',kd.`key`)+1,3) 
AND 
     m.`MACHINE` = SUBSTR(kd.`key`,LOCATE('.i.',kd.`key`)+3,3) 

工作演示在http://sqlfiddle.com/#!2/7d814b/17

Answer 2

SELECT k.id AS key, m.id AS machine 
FROM KPIs k, MACHINE m 
WHERE EXISTS ( 
    SELECT 1 FROM KPIDATA x 
    WHERE x.key LIKE 'k.' + k.id + '.i.' + m.id + '.a.%');