Can we join tables without primary key?

Question

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. 6 авг. 2020 г.

Does a joining 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 primary and foreign 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. No relationship needs to explicitly exist.

Is it okay to have a table without primary key?

Every table can have (but does not have to have) a primary key. The column or columns defined as the primary key ensure uniqueness in the table; no two rows can have the same key. The primary key of one table may also help to identify records in other tables, and be part of the second table's primary key.

Can I join on non primary key?

You aren't required to have the primary key column in a JOIN (though, it usually is faster because of indexes). Just use your common field as the join criteria: SELECT a. field, b.

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