Can a child table have two parent tables?

Can a child table have two parent tables?

It depends. In general, you would like to have foreign key relationships. If there is only one comment allowed per question/answer, then it is easy. A commentId goes in each of the tables, Questions and Answers .

Can there be two relationships between two tables?

EDIT: Yes, of course there can be two relationships between the same two tables. You’ll need to add an extra table (i.e. four tables instead of three) or to add some kind of is_preferred flag in the employer2employee table). Yes, it is allowed.

What happens when you join two tables?

Different Types of SQL JOINs (INNER) JOIN : Returns records that have matching values in both tables. LEFT (OUTER) JOIN : Returns all records from the left table, and the matched records from the right table. RIGHT (OUTER) JOIN : Returns all records from the right table, and the matched records from the left table.

What are parent tables?

Child tables and parent tables are just normal database tables, but they’re linked in a way that’s described by a parent–child relationship. It’s usually used to specify where one table’s value refers to the value in another table (usually a primary key of another table).

How do you select from multiple tables in SQL without join?

You can wrap a query like this in a set of parenthesis, and use it as an inline view (or “derived table”, in MySQL lingo), so that you can perform aggregate operations on all of the rows. If your question was this — Select ename, dname FROM emp, dept without using joins..

Can we join 4 tables in SQL?

If you have to join another table, you can use another JOIN operator with an appropriate condition in the ON clause. In theory, you can join as many tables as you want.

How do you join two tables with many-to-many relationships?

To avoid this problem, you can break the many-to-many relationship into two one-to-many relationships by using a third table, called a join table. Each record in a join table includes a match field that contains the value of the primary keys of the two tables it joins.

What is an example of a one-to-one relationship?

A one-to-one relationship exists when each row in one table has only one related row in a second table. For example, a business might decide to assign one office to exactly one employee. Thus, one employee can have only one office. The same business might also decide that a department can have only one manager.

How do I merge two tables in Excel?

Combine tables in Excel by column headers

1. On your Excel ribbon, go to the Ablebits tab > Merge group, and click the Combine Sheets button:
2. Select all the worksheets you want to merge into one.
3. Choose the columns you want to combine, Order ID and Seller in this example:
4. Select additional options, if needed.

How many tables may be included with a join?

How many tables may be included with a join? Explanation: Join can be used for more than one table.

What is a parent key?

A parent key is either a primary key or a unique key in the parent table of a referential constraint. This key consists of a column or set of columns. The values of a parent key determine the valid values of the foreign key in the constraint. This column (or set of columns) is called the parent key of the table.

How do I get multiple columns from multiple tables in SQL?

Example syntax to select from multiple tables:

1. SELECT p. p_id, p. cus_id, p. p_name, c1. name1, c2. name2.
2. FROM product AS p.
3. LEFT JOIN customer1 AS c1.
4. ON p. cus_id=c1. cus_id.
5. LEFT JOIN customer2 AS c2.
6. ON p. cus_id = c2. cus_id.

How do you select data from multiple tables?

A simple SELECT statement is the most basic way to query multiple tables. You can call more than one table in the FROM clause to combine results from multiple tables.

Can we Natural join 3 tables?

Theoretically, there is no upper limit on the number of tables that can be joined using a SELECT statement. (One join condition always combines two tables!) Example 1 joins three tables of the sample database.

How do I join more than two tables?

When joining more than two tables, you do not have to use the same join type for every join. To join tables by using more than one join type, specify the join types in the FROM clause.

What is a many-to-many join?

A many-to-many relationship occurs when multiple records in a table are associated with multiple records in another table. Each record in a join table includes a match field that contains the value of the primary keys of the two tables it joins.

What is the difference between one-to-one and one to many?

One-to-one relationships associate one record in one table with a single record in the other table. One-to-many relationships associate one record in one table with many records in the other table.

How do I join two tables together?

1. Click on the table you want to drag, then the cross sign will be appeared, then click the cross sign to select the whole table. 2. Press Shift + Alt + Up arrow until the selected table is joined to above one.

How do I merge two tables in Excel with one column?