Can't SELECT records from two tables properly - mysql

Question

I've been using this Query at first, Then used this Query at last
Which are
##Query[1]
SELECT t.title, p.content, p.version
FROM drafts d
INNER JOIN titles t ON t.id = d.tp_id AND d.t = 1
INNER JOIN posts p ON p.id = d.tp_id AND d.t = 2
WHERE user_id = 1
##Query[2]
SELECT coalesce(p.title, t.title), p.content, p.version
FROM drafts d
INNER JOIN titles t ON t.id = d.tp_id AND d.t = 1
INNER JOIN
(
SELECT pt.id, tp.title, pt.content, pt.version
FROM posts pt
INNER JOIN titles tp ON tp.id = pt.tid
) p ON p.id = d.tp_id AND d.t = 2
WHERE user_id = 1
What I want to do Using the Table: drafts to use
Column: tp_id as an identifier to the Column: id in other tables.
Column: user_id as the id of the user having the draft.
Column: t as the identifier to which table of Tables: titles[t=1], posts[t=2] to fetch the records from it.
In Table: posts the Column: tid links to the Column: id of Table: titles Which is used to pull the Column: title.
I want no records to be shown from the Table: titles if doesn't exist, And no records to be shown from the Table: posts if the title related using tid on Table: titles doesn't exist Or the record of the Table: posts doesn't exist, That why I used INNER JOIN.
But in both queries I don't get any results at all.
Is this even the proper table scheme and design to be used for something like the Drafts table for two different tables instead of one for each table?
The result I expect is something like this
title content version
TheTitle null null
TheTitle Content1 1
TheTitle Content2 2
TheTitle Content3 3
TheTitle Content4 4
TitleThe Content1 1
TitleThe Content2 2
TitleThe Content3 3
TitleThe Content4 4
A simple Example:
[table-a] [table-b]
[id - title ] [id - table_a_id - content ]
[1 - title-1] [1 - 1 - content-1]
table-a has the titles.
table-b has the content of each
title.
table-b column of table_a_id links the content with
the title of table-a.
[table-ab]
[user_id - table_col_id - table_letter]
[1 - 1 - a ]
[1 - 1 - b ]
table-ab has user_id to tell which user will be shown the records.
table-ab has table_letter to tell the query which table to fetch the data from it.
What I want the Query to do is to check table-ab and fetch the data from the other tables according to it, so it would be
table_letter = a => fetching rows from table-a.
table_col_id = 1 => fetching rows from table-a WHERE id = 1.
result = title-1
table_letter = b => fetching rows from table-b.
table_col_id = 1 => fetching rows from table-b WHERE id = 1.
result = title-1 - content-1
Final result:
id - title - content
-------------------------
1 - title-1 - null
2 - title-1 - content-1

Answer 1

Do two separate queries (for t=1 and t=2) and use UNION ALL to combine the results:
SELECT t.title, null content , null version
FROM drafts d
INNER JOIN titles t
ON t.id = d.tp_id
WHERE d.user_id = 1 and d.t = 1
UNION ALL
SELECT pt.title, pt.content, pt.version
FROM drafts d
INNER JOIN
( SELECT p.id, t.title, p.content, p.version
FROM posts p
INNER JOIN titles t ON t.id = p.tid ) pt
ON pt.id = d.tp_id AND d.t = 2
WHERE d.user_id = 1

Answer 2

As you are using inner join so please check the following:
Common data in both tables(joining column), if there will not be any common value it will not pick any thing.
Check data type of the column which are used to join both table that should be same if not then handle it
Extra spaces in the joining column.

Answer 3

After joining with condition d.t = 1 there is no data for d.t = 2 That's why after 2nd Join you are not getting any data. Try the below Query
SELECT coalesce(p.title, t.title), p.content, p.version
FROM drafts d
INNER JOIN titles t
ON t.id = d.tp_id
INNER JOIN
(
SELECT pt.id, tp.title, pt.content, pt.version
FROM posts pt
INNER JOIN titles tp
ON tp.id = pt.tid
) p
ON p.id = d.tp_id
WHERE user_id = 1
AND (d.t = 1 OR d.t = 2)

Answer 4

This will produce almost exactly what you have in your question. It does omit the line with the null values for the content and version. Not sure why that would have been in the expected output.
SELECT
if(d.t = 1,tp.title, if(d.t = 2,t.title,"")) as `title`,
p.content,
p.version
FROM drafts d
LEFT JOIN titles t ON t.id = d.tp_id AND d.t = 2
LEFT JOIN posts p ON t.id = p.tid
LEFT JOIN titles tp ON tp.id = p.tid AND d.t = 1
WHERE user_id = 1 AND NOT p.content IS NULL
I changed some of the data, specifically the groups of Content1 - Content4. I added "a" to the first 4, and "b" to the remainder.
Here's a SQL Fiddle that shows what it does.