Can join be used without foreign key?
You don’t need a FK, you can join arbitrary columns. But having a foreign key ensures that the join will actually succeed in finding something. Foreign key give you certain guarantees that would be extremely difficult and error prone to implement otherwise.
Do you need foreign keys to join tables?
A declared foreign key relationship is not necessary for using join . Foreign keys are not needed to join tables!
How can I join two tables without joining condition in SQL?
Yes, Tables Can Be Joined Without the JOIN Keyword You can replace it with a comma in the FROM clause then state your joining condition in the WHERE clause. The other method is to write two SELECT statements. The result of each is a table, so simply use UNION or UNION ALL to combine the two.
How can I join two tables without common column in SQL?
Using the “FROM Table1, Table2” Syntax One way to join two tables without a common column is to use an obsolete syntax for joining tables. With this syntax, we simply list the tables that we want to join in the FROM clause then use a WHERE clause to add joining conditions if necessary.
Can a table have foreign key without primary key?
Primary keys always need to be unique, foreign keys need to allow non-unique values if the table is a one-to-many relationship. It is perfectly fine to use a foreign key as the primary key if the table is connected by a one-to-one relationship, not a one-to-many relationship.
How can I join without condition?
We can use ‘cross join’ without on condition. Cross join gives the result in cartesian product form. For instance, if in one table there are 3 records and another table has 2 records, then the first record will match with all the second table records. Then, the same process will be repeated for second record and so on.
Can we use inner join without on condition?
When using join or inner join , the on condition is optional. This is different from the ANSI standard and different from almost any other database. The effect is a cross join . Similarly, you can use an on clause with cross join , which also differs from standard SQL.
Are foreign keys necessary?
The FOREIGN KEY constraint is crucial to relational database design. It lets us link the data according to our needs. As it creates some dependencies between the columns of primary and foreign tables, it also lets us decide what to do ON UPDATE and ON DELETE actions performed on the rows of the primary table.
Does FK improve performance?
It’s a common mistake to avoid creating foreign keys in a database because they negatively impact the performance. It is true that foreign keys will impact INSERT, UPDATE and DELETE statements because they are data checking, but they improve the overall performance of a database.
How do you join two tables without common values?
3 Answers
- We can use the Cartesian product, union, and cross-product to join two tables without a common column.
- Cartesian product means it matches all the rows of table A with all the rows of table B.
- Union returns the combination of result sets of all the SELECT statements.
Can we join two tables without any relation in SQL?
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 an entity have only foreign keys?
There is no problem having a table that consists of foreign keys only. In your particular example it would be OK to remove the OrderID. Relational theory states that each table should have a candidate key so, ideally, the business rule you mention would be in place to make the foreign key only table a “good” table.
How do you join a table without common fields?
What happens when you join two tables together without an on clause?
Any JOIN without an ON clause is a CROSS JOIN. The LEFT JOIN is an outer join, which produces a result set with all rows from the table on the “left” (t1); the values for the columns in the other table (t2) depend on whether or not a match was found.
Can you join without a condition SQL?
Can we write inner join without on condition?
How do I join without on condition?
Does a foreign key make joins faster?
Yes it will improve the performance of you db if you are checking integrity using foreign key instead of running many queries for checking the record is exist in database in your program. Show activity on this post. You can use it to help make a query more efficient.
Can we join two tables without any relation in mysql?
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.
How do I join two tables in SQL without duplicates?
Linked
- Merge into (in SQL), but ignore the duplicates.
- Using UNION to combine same SQL Tables and searching for a specific word return duplicate rows.
- Copy data from one table to another without creating duplicate records SQL.
- Join 2 tables in SQL without duplicates.
Can we use foreign keys in Entity Framework?
Luckily, entity framework is smart enough, that if you design it properly, you will seldom use the foreign keys to perform (group)joins. You usually use the virtual properties. In entity framework the classes represent the tables of your database.
Can Entity Framework be used for group-joins?
Luckily, entity framework is smart enough, that if you design it properly, you will seldom use the foreign keys to perform (group)joins. You usually use the virtual properties.
Do I need a foreign key to the employer?
For this every Employee needs a foreign key to the Employer it belongs to, whether you like it or not. Luckily you won’t have to use it.
Can I use Entity Framework Code first conventions for classes?
Using the entity framework code first conventions your classes would need a slight change: the relations between the tables should be marked virtual.