32. Basic SQL

Structured Query Language (SQL) is a programming language used to manage and manipulate relational databases. SQL allows users to access, modify, view and manipulate their data efficiently and easily. This chapter of our logic programming course will cover the basics of SQL, from creating tables to running complex queries.

Understanding SQL

SQL is a declarative language, which means the user specifies what they want (eg, retrieve data, update data), and the database system figures out how to accomplish the task. In other words, the user doesn't have to specify how to get the data, just what they want to get.

Basic SQL Commands

There are four basic SQL commands that every programmer should know: SELECT, INSERT, UPDATE, and DELETE. These commands allow the user to retrieve, add, modify and delete data in a database.

SELECT

The SELECT command is used to retrieve data from a database. The basic syntax is:

SELECT column_name(s)
FROM table_name;

For example, to select all data from the 'name' column of the 'customers' table, you would use:

SELECT name
FROM customers;

INSERT

The INSERT command is used to insert new records into a table. The basic syntax is:

INSERT INTO table_name (column1, column2, column3,...)
VALUES(value1, value2, value3,...);

For example, to insert a new customer into the 'customers' table, you would use:

INSERT INTO customers (name, email)
VALUES('John', 'joao@email.com');

UPDATE

The UPDATE command is used to modify existing records in a table. The basic syntax is:

UPDATE table_name
SET column1 = value1, column2 = value2,...
WHERE condition;

For example, to update a customer's email in the 'customers' table, you would use:

UPDATE customers
SET email = 'new@email.com'
WHERE name = 'John';

DELETE

The DELETE command is used to delete existing records in a table. The basic syntax is:

DELETE FROM table_name
WHERE condition;

For example, to delete a customer in the 'customers' table, you would use:

DELETE FROM customers
WHERE name = 'John';

Conclusion

The basic SQL commands above are just the tip of the iceberg when it comes to working with SQL databases. However, understanding these fundamentals is essential for any programmer. In the next chapter, we'll explore more advanced topics in SQL, including joins, subqueries, and aggregate functions.

We hope that this chapter has provided you with a solid introduction to SQL and that you are eager to learn more about this powerful programming language.