Introduction to Databases
A database is a data management tool. Fundamentally, databases effectively facilitate operations including adding, searching, updating, and removing discrete pieces of data. They are crucial for classifying your data and simplifying these processes. When it comes to organising and managing data, databases excel. Databases can be thought of as files that hold data tables.
- Databases have a number of important benefits over flat files for data storage.
- Compared to flat files, they can offer faster data access.
- It is simple to query them to retrieve data sets that meet specific requirements.
- As a programmer, you don’t have to worry about concurrent access because they have built-in techniques for handling it.
Many storage and retrieval operations in a web application are made simpler, safer, and more effective by relational database systems. Almost any collection of data, including user or client information, can be stored in a database for future searches and updates. Products, records of society or club members, names, passwords, addresses, email addresses, registration dates, blog posts, and phone numbers can all be kept in databases.
One or more tables make up a database. Specific data structures are defined in tables. As the name suggests, a table is a table of data, much like an electronic spreadsheet. Every table has rows and columns. Records are the rows that make up database tables.
Relational Databases (RDBMS)
The most popular kind of database is a relational database. They enable the development of links, or relations, between various kinds of information and provide detailed data structure. An RDBMS manages this organised data.
RDBMS include MySQL, Oracle, PostgreSQL, Sybase, and SQL Server. A quick and stable relational database management system, MySQL is the most popular open-source database.
Data may be dispersed among multiple tables in a relational database. A common key can be used to connect related data that is kept in different tables. Table relationships are categorised as one-to-one, one-to-many, or many-to-many depending on how many elements are involved. A relationship between data in two tables is represented by foreign keys.
Structured Query Language (SQL)
Structured Query Language is what SQL stands for. The most widely used language for relational database management system access is this one. In addition to creating, modifying, and querying relational databases, SQL is used to store and retrieve data from databases. In SQL, queries are another name for commands.
There are two components to SQL syntax:
Data Definition Language (DDL): Database definition and structural modification are done using the Data Definition Language (DDL). When you first build up a database, you utilise DDL.
Data Manipulation Language (DML): Data in an existing database can be retrieved and modified using the Data Manipulation Language (DML). Since DML components are used to store and retrieve actual data, you will utilise them far more often than DDL. SELECT, INSERT, UPDATE, and DELETE are the fundamental DML operations.
SQL Code Examples
Using a fictitious “books” database that is frequently discussed in the following are some instances of typical SQL commands that are based on procedures described:
- Creating a Database: A method for developing a new database system.
- Regarding the ‘Book-O-Rama’ illustration:
- Selecting a Database: This is how you indicate the MySQL server database you wish to work with.
- The ‘books’ database:
- Showing Databases: Provides a list of the databases that are accessible on the server.
- Creating a Table: Specifies the format of a new table in the database of choice. You substitute the desired name for the tablename and a list of column definitions (name followed by data type) separated by commas for the columns.
- According to the ‘Books’ table description:
- According to the description field from DESCRIBE Books; output, which shows these constraints, NOT NULL and PRIMARY KEY were added.
- Showing Tables: Provides a list of every table in the database that is now selected.
- Giving details about the columns of a particular table is known as table description.
- Regarding the ‘Books’ tab:
- Adding additional rows of data to a table is done by inserting data.
- To the Books table, add a row:
- Retrieving Data (SELECT): To retrieve data from one or more tables, use the Retrieving Data (SELECT) function. The fundamental DML command for data queries is this one.
- An example of choosing the author and title from the Books table when the price exceeds thirty
- Choosing every column in the Books table, for instance:
- Joining Tables: Table joining is the process of combining rows from two or more tables according to a shared column. The EXPLAIN provide an example of a difficult join involving four tables:
- This query links the Customers, Orders, Order_Items, and Books tables using their associated columns to extract the names of customers who ordered books containing the word “Java” in their titles.
- Updating Data: A table’s existing records can be changed using this method.
- Deleting Data: Data deletion is the process of deleting entries from a table.
- Dropping Tables/Databases: This technique is used to eliminate databases or tables altogether.
A SELECT query can be preceded by the EXPLAIN statement, which provides details about the query plan and helps you understand how MySQL runs the query.
Part II of “Using MySQL” covers the principles of relational databases and SQL. This section of the book covers the general operation of relational databases, as well as how to use SQL and set up MySQL to develop database-backed websites.