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POUnable to implement join properly
 

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    <p>I am trying to figure out</p> <p>(book_id, branch_id, total_copies, number_available)</p> <p>Here is the schema: <img src="https://i.stack.imgur.com/K4qhp.jpg" alt="enter image description here"></p> <p>Here is as far I have gone:</p> <pre><code>SELECT TITLE, A.BOOK_ID, A.BRANCH_NAME, A.BRANCH_ID, NO_OF_COPIES, COUNT(BOOK_LOANS.BOOK_ID) AS NUM_OUT, NO_OF_COPIES - COUNT(BOOK_LOANS.BOOK_ID) AS NUM_AVAIL, AUTHOR_NAME FROM (SELECT TITLE, BOOK.BOOK_ID, BOOK_COPIES.BRANCH_ID, BRANCH_NAME, NO_OF_COPIES, BOOK_AUTHORS.AUTHOR_NAME FROM BOOK, BOOK_COPIES, LIBRARY_BRANCH, BOOK_AUTHORS WHERE BOOK_COPIES.BOOK_ID=BOOK.BOOK_ID AND BOOK_AUTHORS.BOOK_ID = BOOK.BOOK_ID AND ( BOOK.TITLE LIKE :title OR BOOK.BOOK_ID = :book_id OR BOOK_AUTHORS.AUTHOR_NAME LIKE :author_name ) AND BOOK_COPIES.BRANCH_ID=LIBRARY_BRANCH.BRANCH_ID) AS A LEFT OUTER JOIN BOOK_LOANS ON A.BOOK_ID=BOOK_LOANS.BOOK_ID AND A.BRANCH_ID=BOOK_LOANS.BRANCH_ID GROUP BY A.BOOK_ID, A.BRANCH_ID </code></pre> <p>But the problem I am encountering is, since BOOK_AUTHORS table has multiple authors for a single book. So I am able to understand that joining only on book_id of BOOK and BOOK_AUTHORS while I should be able to completely using the both book_id and author_name.</p> <p>So its returning the count 2 times for a single entry in book_loans.</p> <p>e.g. If a book with book_id lets say 1234 is checked out once, and it has total copies of 2, so it should return remaining copies as 1. But its returning 0.</p> <p>Please help me understand how to fix this.</p> <p>Note: I am using php prepare statement.</p>
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    1. USJason Heo
    1. USpk10
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    1. COas far as schema is concerned i think there should be a table called `authors_master` having two columns `author_id,author_name` so that it can be mapped to book using a table `book_author` having only two columns `book_id,author_id`
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      1. USManoj Purohit
    2. COThat might be a solution, but that's what I have been given to work on.
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      1. USpk10
 

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