SQL (Structured Query Language) is a programming language designed for managing relational databases. It is used to store, manipulate, and retrieve data from databases. SQL has become the standard language for working with relational databases and is supported by all major database management systems.
History of SQL
SQL was first developed in the 1970s by IBM researchers Raymond Boyce and Donald Chamberlin. It was initially called SEQUEL (Structured English Query Language), but was later changed to SQL due to trademark issues. SQL became an ANSI (American National Standards Institute) standard in 1986 and an ISO (International Organization for Standardization) standard in 1987.
SQL is a declarative language, which means that you tell it what you want to do, and it figures out how to do it. The basic SQL commands are:
SELECT: used to retrieve data from one or more tables.
INSERT: used to add new rows to a table.
UPDATE: used to modify existing rows in a table.
DELETE: used to delete rows from a table.
CREATE: used to create a new table, view, or index.
ALTER: used to modify the structure of a table or view.
DROP: used to delete a table, view, or index.
SQL statements are written in a specific syntax that consists of keywords, clauses, expressions, and operators. Here is an example of a simple SQL statement:
SELECT * FROM customers;
This statement selects all the rows and columns from the
customers table. The
SELECT keyword is followed by a list of columns to retrieve or the
* wildcard to select all columns. The
FROM keyword is followed by the table name.
SQL Data Types
SQL supports a variety of data types, including numeric, string, date/time, and boolean. The data type of a column is defined when the table is created using the
CREATE TABLE statement. Here are some common data types in SQL:
INTEGER: a whole number.
FLOAT: a decimal number.
VARCHAR: a variable-length string of characters.
DATE: a date in the format
TIME: a time in the format
BOOLEAN: a value that can be either
One of the most powerful features of SQL is its ability to join tables together to create more complex queries. SQL supports four types of joins: inner join, left join, right join, and full outer join. Here is an example of an inner join:
SELECT customers.name, orders.order_date
INNER JOIN orders
ON customers.id = orders.customer_id;
This statement joins the
customers table with the
orders table on the
customer_id columns, respectively. The
SELECT clause retrieves the
name column from the
customers table and the
order_date column from the
SQL is a powerful language that is widely used for managing relational databases. This article provided a brief introduction to SQL, including its history, basics, syntax, data types, and joins. With this knowledge, you should be able to start writing your own SQL queries and manipulating data in a database.
Next, if you’re interested in further exploring the capabilities of SQL, you may find these articles helpful:
- SQL Select (with Distinct and Top): This article explains how to use the SELECT statement in SQL to retrieve data from one or more tables in a database, including how to use the DISTINCT and TOP keywords to refine your queries.
- SQL WHERE with AND, OR, NOT Operators: This article explores the WHERE clause in SQL, including how to use logical operators such as AND, OR, and NOT to filter your query results based on multiple conditions.