使用左联接联接多个表（其中联接的表之一中不存在条目）不返回任何内容

Question

I have 4 tables that have to be joined on more than a single field, and can't get it to work when table 3 has no data

T1

id primary key
user_id
mydata

T2

id primary key
user_id
entry_id
mydata

T3

id primary key
user_id
entry_id
mydata

T4

id primary key
user_id
entry_id
mydata

I want to return all of T1 where a search string matches any of the other 3 tables:

SELECT DISTINCT(id) as id FROM T1
LEFT JOIN T2 ON (T1.user_id = T2.user_id AND T2.entry_id = T1.id)
LEFT JOIN T3 ON (T1.user_id = T3.user_id AND T3.entry_id = T1.id)
LEFT JOIN T4 ON (T1.user_id = T4.user_id AND T4.entry_id = T1.id)
AND (T1.mydata LIKE :s OR T2.mydata LIKE :s OR T3.mydata LIKE :s OR T4.mydata LIKE :s)

The query works when all tables have entries, but when say T3 has no entries matching entry_id, nothing is returned.

What am I doing wrong, I can't seem to solve this... please help

Answer 1

I managed to fix the problem by replacing AND with WHERE, so this:

SELECT DISTINCT(id) as id FROM T1
LEFT JOIN T2 ON (T1.user_id = T2.user_id AND T2.entry_id = T1.id)
LEFT JOIN T3 ON (T1.user_id = T3.user_id AND T3.entry_id = T1.id)
LEFT JOIN T4 ON (T1.user_id = T4.user_id AND T4.entry_id = T1.id)
AND (T1.mydata LIKE :s OR T2.mydata LIKE :s OR T3.mydata LIKE :s OR T4.mydata LIKE :s)

becomes:

SELECT DISTINCT(id) as id FROM T1
LEFT JOIN T2 ON (T1.user_id = T2.user_id AND T2.entry_id = T1.id)
LEFT JOIN T3 ON (T1.user_id = T3.user_id AND T3.entry_id = T1.id)
LEFT JOIN T4 ON (T1.user_id = T4.user_id AND T4.entry_id = T1.id)
WHERE (T1.mydata LIKE :s OR T2.mydata LIKE :s OR T3.mydata LIKE :s OR T4.mydata LIKE :s)

It seems the AND was causing the search criteria to become part of the last left join or something.