Introduction to SQL

Communication with relational DBMS happens in SQL. It is used to perform all the main database operations:

Data

SELECTExtract data from a database

INSERTInsert records into a database

UPDATEUpdate records in a database

DELETEDelete records from a database

Structure

CREATE DATABASECreate new databases

CREATE TABLECreate new tables in a database

Logic and access

CREATE PROCEDURECreate stored procedures

CREATE VIEWCreate views

GRANTSet permissions for tables, procedures, and views

SQL dialects (SQL extensions)

SQL is a universal language for all relational database management systems, but many DBMS make changes to the language they use, thus deviating from the standard. Such languages are called dialects or extensions of the language.

Here are some of them. As an example, let's see how each of these DBMS selects the first 3 rows.

T-SQL

SELECT TOP 3 name

Microsoft SQL Server

PL/SQL

WHERE ROWNUM <= 3

Oracle Database

MySQL

name LIMIT 3

PL/pgSQL

name LIMIT 3

PostgreSQL

Which dialect to learn?

If you know that you need to learn SQL, you should learn standard SQL. However, if you already know which specific database you will be working with, it is probably best to learn its SQL dialect and just know that different databases may use slightly different syntax.

In our course, we offer you a choice between MySQL DBMS and PostgreSQL DBMS, as the 2 most popular solutions. Try picking one right now — every example and exercise in the course will adapt to your choice:

You can switch the DBMS at any time — right here, in the gear icon menu in the site header or in the code editor.