Join three MySQL tables so that I don't get repeating data - mysql

Question

I have three mysql table tblOne, tblTwo and tblThree
SELECT tblOne.bookID AS bookID,
tblOne.title AS title,
tblOne.author AS author,
tblOne.blurb AS blurb,
tblOne.isbn AS isbn,
tblOne.coverImage As coverImage,
CONCAT_WS(" ", tblThree.firstName, tblThree.lastName) AS fullName,
tblTwo.rating,
tblTwo.reviewText AS review,
CONCAT_WS(" ", tblTwo.reviewDate, tblTwo.reviewTime) AS reviewDate
FROM tblTwo
INNER JOIN tblOne
ON tblTwo.bookID = tblOne.bookID
INNER JOIN tblThree
ON tblTwo.userID = tblThree.userID
WHERE tblTwo.bookID = 1000102;
The output populates an XML file, for this book, there are two reviews and as such the data for title, author etc is pulled twice. How can I overcome this as when I try to access the tag from within a JavaScript query, it fails as it says it is undefined. I think that this is due to having more than one result.
The above SQL actually does work, my PHP was erroneous, however...
How can I return the book details even when there is no review? Currently, only books that have been reviewed get their details returned.

Answer 1

You are using INNER JOIN, which requires rows to exist in joined table. Use LEFT JOIN instead, which returns rows from the first-listed table even if rows from the left-joined table don't exist:
SELECT tblBooks.bookID AS bookID,
tblBooks.title AS title,
tblBooks.author AS author,
tblBooks.blurb AS blurb,
tblBooks.isbn AS isbn,
tblBooks.coverImage As coverImage,
CONCAT_WS(' ', tblMembers.firstName, tblMembers.lastName) AS fullName,
IFNULL(tblReviews.rating, '0'),
tblReviews.reviewText AS review,
CONCAT_WS(' ', tblReviews.reviewDate, tblReviews.reviewTime) AS reviewDate
FROM tblBooks
LEFT JOIN tblReviews
ON tblReviews.bookID = tblBooks.bookID
LEFT JOIN tblMembers
ON tblReviews.userID = tblMembers.userID
GROUP BY 1, 2, 3, 4, 5, 7, 8;
Notice that I've listed tblOne first in the FROM clause, which is necessary to get all books even if some have no reviews.
You'll have to deal with null values when there are no reviews. Consider using IFNULL() to generate blanks or a default value, eg
IFNULL(tblTwo.rating, '') -- instead of just tblTwo.rating
Or
IFNULL(tblTwo.reviewText, 'None') -- instead of just tblTwo.reviewText
etc

Answer 2

SQL will always form the cartesian product between the tables meaning that if you have one book with 2 reviews and each review has 3 tags, you will have 6 rows returned to cover all of the data combinations.
You cannot have one book per row if you are joining on a table where the number of expected elements per join is greater than 1. You will need to restructure the XML logic (not sure how you go from SQL -> XML) to cluster taking the redundancies into account.

Answer 3

use GROUP_CONCAT and join the table/table_three results. Try something like:
SELECT tblOne.bookID AS bookID,
tblOne.title AS title,
tblOne.author AS author,
tblOne.blurb AS blurb,
tblOne.isbn AS isbn,
tblOne.coverImage As coverImage,
GROUP_CONCAT(
(SELECT CONCAT_WS(" ", tblThree.firstName, tblThree.lastName)
AS fullName,
tblTwo.rating,
tblTwo.reviewText AS review,
CONCAT_WS(" ", tblTwo.reviewDate, tblTwo.reviewTime)
AS reviewDate
FROM tblTwo INNER JOIN
tblOne ON tblTwo.bookID = tblOne.bookID
INNER JOIN
tblThree ON tblTwo.userID = tblThree.userID
WHERE tblTwo.bookID = 1000102)
SEPARATOR ' '
)
FROM tblTwo INNER JOIN
tblOne ON tblTwo.bookID = tblOne.bookID
INNER JOIN
tblThree ON tblTwo.userID = tblThree.userID
WHERE tblTwo.bookID = 1000102;