User Tables and System Tables

User Tables

User tables are the primary repository of data in a database management system (DBMS). They are created and managed by the database administrator (DBA) or the end-users themselves and store the data that is relevant to their business or personal needs. This type of table is usually called a "user table" because it is created and managed by the user and not the DBMS itself.

User tables can have any number of columns and rows and can be used to store a wide variety of data types, including text, numbers, dates, and binary data. The columns in a user table are defined with specific data types, such as integer, float, or string, and can have constraints placed on them to enforce data integrity. For example, a column may be defined as a primary key, which ensures that no two rows in the table have the same value for that column.

User tables are used to store data in a variety of applications, including enterprise resource planning (ERP) systems, customer relationship management (CRM) systems, and data warehouses. They are also commonly used to store data for web applications and mobile applications.

System Tables

System tables, also known as system catalogs, store metadata about the database, including its structure, physical details, performance statistics, and security settings. The DBMS automatically creates and maintains these tables, and the information they contain is used to manage and optimize the database.

System tables contain information such as the names of tables, columns, and indexes, the data types of columns, the relationships between tables, and the access privileges for users. This information is used by the DBMS to enforce data constraints and to optimize queries.

One important use of system tables is to support database optimization. For example, the DBMS uses the information in the system tables to determine the best way to execute a query. This information includes statistics about the distribution of data in the tables, the size of the tables, and the number of rows in each table.

Another use of system tables is to support data recovery. The DBMS uses information in the system tables to keep track of changes to the data in the user tables. If a problem occurs that causes data to be lost, the DBMS can use the information in the system tables to recover the data.

Example of a User Table:

Consider a small online store that sells books. The database for this store might have a user table named "Books" that stores information about each book available for sale. The table might have columns for the book's title, author, publication date, ISBN number, price, and stock level. Here is an example of what the table might look like:

Title,Author,Publication,ISBN,Price,Stock
The Great Gatsby,F. Scott Fitzgerald,1925-04-10,978-0679722796,15.99,50
To Kill a Mockingbird,Harper Lee,1960-07-11,978-0446310789,14.99,75
1984,George Orwell,1949-06-08,978-0451524935,12.99,100

Example of a System Table:

In the same database, there might be a system table named "Tables" that stores information about the structure of the database. The table might have columns for the table name, the number of columns in the table, the number of rows in the table, and the date the table was created. Here is an example of what the table might look like:

Table,Columns,Rows,Date Created
Books,6,3,2022-12-01
Customers,4,100,2022-11-15

In this example, the system table "Tables" contains information about the user tables in the database. This information can be used by the DBMS to enforce data constraints and to optimize database performance. In summary, user tables and system tables are two different types of tables in a database management system. User tables store the data that is relevant to the end users, while system tables store metadata about the database and its structure. Understanding the difference between user tables and system tables is important for proper database management and optimization.

Reference

Fehily, C. (2008). "Learn SQL the Quick and Easy Way."