Does a join table need a primary key?
A table must have exactly one primary key to qualify as relational, but that key can be composed of multiple columns.
A foreign key, by contrast, is one or more fields or columns that corresponds to the primary key of another table.
Foreign keys are what make it possible to join tables to each other..
Can we join two tables without common column?
Yes, you can! The longer answer is yes, there are a few ways to combine two tables without a common column, including CROSS JOIN (Cartesian product) and UNION. The latter is technically not a join but can be handy for merging tables in SQL. In this article, I’ll guide you through the different solutions with examples.
What Cannot be done if the table has no primary key?
If you don’t have a candidate key in you data, just create a surrogate one ( AUTO_INCREMENT , SERIAL or whatever your database offers). The only excuse for not having a PRIMARY KEY is a log or similar table which is a subject to heavy DML and having an index on it will impact performance beyond the level of tolerance.
Can we join two tables without any relation?
The answer to this question is yes, you can join two unrelated tables in SQL and in fact, there are multiple ways to do this, particularly in the Microsoft SQL Server database. The most common way to join two unrelated tables is by using CROSS join, which produces a cartesian product of two tables.
Can you use the same primary key for two tables?
Yes two table can have the same primary key. … Primary key used to identify the unique row/record in a table. So you can create a same column as a primary key in multiple tables.