Introduction to SQL
SQL (Structured Query Language) can be considered as the standard database access language. Today it is supported by most commercial products, whether by micro database management systems such as Access or by more professional products such as Oracle. It has been the subject of several ANSI / ISO standards, the most widespread of which is the SQL2 standard which was defined in 1992.
What is SQL?
The SQL language (Structured Query Language) is an international standard, as regards the languages used to manipulate databases. SQL is known by all RDBMSs. It should however be mentioned that, now with the presence of international standards such as SQL-86, SQL-89 or SQL-92, each DBMS on the market uses a little its own dialect of the SQL language.
SQL is the standard language for relational database systems. All relational database management systems (RDBMS) such as MySQL, MS Access, Oracle, Sybase, Informix, Postgres and SQL Server use SQL as the standard database language.
Why SQL?
SQL is very popular because it offers the following advantages:
- Allows users to access data from relational database management systems.
- Allows users to describe the data.
- Allows users to define and manipulate data in a database.
- Allows you to integrate into other languages using SQL modules, libraries and pre-compilers.
- Allows users to create and delete databases and tables.
- Allows users to create a view, stored procedure, and functions in a database.
- Allows users to define permissions on tables, procedures, and views.
SQL commands
The standard SQL provides many command which help us to deal with relational databases such that CREATE, SELECT, INSERT, UPDATE, DELETE and DROP. We can classify these commands into the following groups according to their nature
DDL - Data Definition Language
| Command | Description |
|---|---|
| CREATE | Creates a new table, a view, or another object in the database. |
| ALTER | Modifies an existing database object, such as a table. |
| DROP | Removes an entire table, a view of a table, or other objects from the database. |
DML - Data Manipulation Language
| Command | Description |
|---|---|
| SELECT | Retrieve certain records from one or more tables. |
| INSERT | Create a record. |
| UPDATE | Modifies the records. |
| DELETE | Delete the records. |
DCL - Data Control Language
| Command | Description |
|---|---|
| GRANT | Give privilege to the user. |
| REVOKE | Resumes the privileges granted by the user. |
We will come back to all these commands in detail in the next courses. we hope that you enjoy the courses.
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