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Can we use join without primary key?
A primary key is not required. A foreign key is not required either. You can construct a query joining two tables on any column you wish as long as the datatypes either match or are converted to match.
Is it mandatory to assign primary key?
No, it is not required for every table to have a primary key. Whether or not a table should have a primary key is based on requirements of your database. Even though this is allowed it is bad practice because it allows for one to add duplicate rows further preventing the unique identification of rows.
Can we add foreign key without primary key?
A foreign key can refer to either a unique or a primary key of the parent table. If the foreign key refers to a non-primary unique key, you must specify the column names of the key explicitly.
Why is foreign key used?
A foreign key (FK) is a column or combination of columns that is used to establish and enforce a link between the data in two tables to control the data that can be stored in the foreign key table.
How do you create a relationship to a non primary key in?
Is there any way I can get the cascade update/delete feature without changing the users table so that UserName is the primary key and not UserID? Create a unique index or unique constraint on UserName then you can reference it in a FK constraint fine. is incorrect.
How to join two tables without keys or relations?
I’d like to do this without using many cursors/looping. This will get you every combination of all columns from Table1 and Table2. Thanks for contributing an answer to Stack Overflow! Please be sure to answer the question. Provide details and share your research! But avoid … Asking for help, clarification, or responding to other answers.
How to create a one to many relationship in hibernate?
That being said, I have the need to create a one-to-many, bi-directional relationship in Hibernate (4.2.1) which involves no primary keys (only a unique key on the “parent” side of the relationship) and no join tables. The foreign key representing this relationship is a backpointer from the “child” to the “parent” (see below).
Why do we need a primary foreign key relation in SQL?
To join A through B through C there must be some commonality or your join would either produce zero results or a massive number or results (Cartesian product). If you know this commonality, simply add the needed columns to A and C and link them directly. The rule for relationships is that they simply must have a reason to exist.