Creating a one-to-one relationship between tables with an existing one-to-many relationship
Date : March 29 2020, 07:55 AM
Hope that helps There is nothing (in my opinion) wrong with your initial thought. Although there is a loop as you put it, there isn't a problem here.
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Duplicate tables having N:M relationship (including relationship)
Tag : php , By : OlioEngr
Date : March 29 2020, 07:55 AM
like below fixes the issue You say you can't change the table structure. If you could, I would likely recommend against the denormalization (duplication of rows) of these tables depending upon what you are doing. I'm also a bit confused because you say you have to duplicate the rows and relations with id_category = 1 to id_category = 3, but then your sample queries have id_category = 2. $pdo = new PDO('mysql:host=?', $user, $passwd);
$stmtCustomers = $pdo->prepare("INSERT INTO customer (t_name, id_category)
VALUES (t_name, ?) WHERE id_category = ?");
$stmtContracts = $pdo->prepare("INSERT INTO contract (t_name, id_category)
VALUES (t_name, ?) WHERE id_category = ?");
$stmtRelation = $pdo->prepare("INSERT INTO customer_has_contract VALUES (?, ?)");
//Perform in a loop if needed
$pdo->beginTransaction();
$stmtCustomers->execute($target_cat_id, $origin_cat_id);
$cus_id = $pdo->lastInsertId();
$stmtContracts->execute($target_cat_id, $origin_cat_id);
$con_id = $pdo->lastInsertId();
$stmtRelation->execute($con_id, $cus_id);
$pdo->commit();
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Entity Relationship Diagram. How does the IS A relationship translate into tables?
Date : March 29 2020, 07:55 AM
Hope that helps Assuming the relationship is mandatory (as you said, a person has to be a student or a teacher) and disjoint (a person is either a student or a teacher, but not both), the best solution is with 2 tables, one for students and one for teachers. If the participation is instead optional (which is not your case, but let's put it for completeness), then the 3 tables option is the way to go, with a Person(PersonID, Name) table and then the two other tables which will reference the Person table, e.g. Student(PersonID, GPA), with PersonID being PK and FK referencing Person(PersonID).
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How can we identify the relationship between two SQL Server tables , either one to one or some other relationship.....?
Date : March 29 2020, 07:55 AM
around this issue In SQL Server, create a new view in your database, add the two tables you want to see the relationship with.
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How do I create a relationship between two tables where one already has a relationship with another table?
Date : March 29 2020, 07:55 AM
it should still fix some issue The reason is your Courses table has 2 field in it's primary key. On solution is you add a new field named semesterId in Enrollment table and use both semesterId and courseId when creating foreign key.
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