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Increase fault tolerance By optimally organizing the table schema select. And aggregation queries will work with less data and therefore faster than without normalization. By increasing the number of records in the tables over time this will help maintain a positive user experience. Modeling relationships in relational databases. An illustrative example of modeling complex relationships in relational databases is shown in the figure above. Here we see a database model of an eucational institution. Where there are the following objects student course teacher department direction of study.

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The connection of a teacher with a department is organize through a section and a course foreign keys course id and teacher id in the Section table as well as Department in the Course table . The relationship between a student and a field of study is implemente through the table Students field of study foreign keys student id and field of study id . Thus in order Democratic Republic Of the Congo Email List to calculate for example the number of students in a course and detail the statistics by teachers you nee to write a query with students joining the direction course and teachers making the appropriate grouping by teachers. SQL query language Queries in relational databases are forme using structure SQL.

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Denormalization In addition to normalization there is also a reverse process in relational databases denormalization . It aims to move the most commonly use fields from external tables to internal ones. Lets take a look at the messenger BM Leads example. Denormalization User user leaves messages messages in chats chat . The data structure is such that messages are linke to the user and the chat via foreign keys user from and user to and chat id in the message table user id and chat id in the user chat link table . Since the schema is normalize various queries for selecting counting and aggregating statistics on chats users and messages must be performe using external table joins.

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