MySQL加入多个表

Question

I have three tables:

t1.estimate, t1.mid, t1.description, t1.status

t2.mid, t2.mname, t2.mphone, t2.memail

t3.estimate, t3.action

I need to join these tables, but that issue that I am having is that t2 and t3 may contain no records to join to t1. Table t1 is the primary table that will have the filter applied. Table t2 will 99.9% of the time contain a match when join 'mid'. But table t3 is a table that only stores information and creates an estimate when a user enters it into the table. There can be 40,000 plus records in t1, but only 5,000 in t3.

Here is my current code, but it's only displaying records that are in all three tables. I would like values to be shown from t1 even if there are no records to join on t2 and t3.

SELECT DISTINCT
    t1.estimate, t1.mid, t2.mname, t1.description,
    t1.status, GROUP_CONCAT(t3.action)
FROM t1
LEFT OUTER JOIN t2 ON t1.mid = t2.mid
LEFT OUTER JOIN t3 ON t1.estimate = t3.estimate
WHERE t1.status LIKE '0%'
GROUP BY t3.estimate

Answer 1

您需要更改GROUP BY以使用t1.estimate而不是t3.estimate因为如果没有连接记录， t3.estimate将为NULL。