A foreign key is a field that is linked to another table‘s primary key field in a relationship between two tables.
In relational database management systems, a relationship defines a relationship between two or more tables. That is, the data in one table is related to the data in the other. One table contains the primary key and the other table contains the foreign key.
When we establish a relationship between the tables, we link the foreign key with the primary key. From that point on, any value in the foreign key field should match a value from the primary key field in the other table.
A primary key is a column that has been configured as the unique identifier field for the table.
Any value stored in a primary key field is unique to that record. No other record in that column contains that value. The value is a unique identifier.
In relational database design, a relationship is where two or more tables are linked together because they contain related data. This enables users to run queries for related data across multiple tables.
Relationships are a key element in relational database design.
Here’s an example:
Example of one-to-many relationship.
In the above example, the City table has a relationship with the Customer table. Each customer is assigned a city. This is done by using a CityId field in the Customer table that matches a CityId in the City table.
While it’s certainly possible to store the full city name in the Customer table, it’s better to have a separate table that stores the city details. You can easily use a query to look up the CityName by using the CityId that’s stored for that customer.
To create a macro in Microsoft Access 2013 or 2016:
- Click Macro from the CREATE tab
- Add actions by selecting an action from the combo box
- Customise the actions if required
- Repeat steps 2 and 3 for each action you want to add
- Save the macro
RDBMS stands for Relational Database Management System.
An RDBMS is a particular type of DBMS that uses a relational model for its databases. An RDBMS therefore enables you to create relational databases.
Relational database management systems have become the most popular type of database system. Most major database management systems are relational. Popular examples include Microsoft Access, SQL Server, Oracle Database, MySQL, FileMaker, PostgreSQL, and more below.
There are 3 types of relationships in relational database design. They are:
- One-to-Many (or Many-to-One)
To create a database in the MySQL Workbench GUI:
- Click the “new schema” button on the MySQL Workbench toolbar
- Enter a schema name (database name) and its default collation and click Apply
- Review the SQL statement and click Apply
The database will now be created, and a message will display advising that the script was successful.
To create a table in the MySQL Workbench GUI:
- Under the appropriate database in the left navigation pane, right-click Tables and select Create Table...
- Enter the table name, add all column names, their data type, constraints, default values, and any other details as required, then click Apply
- Review the SQL statement that will be run against the database and click Apply
The table will now be created, and a message will display advising that the script was successful.
To create a table in SQL Server using the GUI:
- Ensuring that the right database is expanded in Object Explorer, right click on the Tables icon and select Table... from the contextual menu
- A new table will open in Design view. Add the columns, their data types, and column properties.
- Save the table (either from the File menu, or by right-clicking on the table tab and selecting Save Table1)
The table will appear in the Object Explorer under the Tables icon for the applicable database.
To create a database in SQL Server using the GUI:
- From the Object Explorer, right click on Databases and select New database...
- Name the database, adjust settings if required, then click OK
Once you’ve created the database, you can create tables and other database objects. You can also modify any database properties as required.