SQL Knowledge Center

Welcome to the SQL Knowledge Center, your one-stop-shop for everything related to SQL. Whether you’re an absolute beginner looking to understand what SQL is all about, or an experienced coder seeking advanced tips and tricks, you’ll find it here.

SQL Introduction

SQL is a standard programming language for database access. SQL language is used to access and manipulate data in any database on the market, such as for MySQL, Oracle, DB2, SQL Server, Access databases. SQL is a structured language and an ANSI standard for accessing and manipulating data in any database.

SQL is composed of SQL statements, each with a different utility, such as:

SQL Advanced

SQL Functions

SQL has predefined functions to perform certain calculations with higher performance.

AVGReturns the average value of a column.
COUNTReturns the number of rows in the query.
FIRSTReturns the first value of the query.
LASTReturns the last value of the query.
MAXReturns the largest value in a column.
MINReturns the smallest value in a column.
SUMReturns the sum of the values in a column.
GROUP BYGroup rows with the same value in a column.
HAVINGInclude conditions with SQL functions.
UCASEConvert a value to uppercase.
LCASEConvert a value to lowercase.
MIDExtracts characters from a text field.
LENReturns the length of a text field.
ROUNDRounds a numeric field to a specified number of decimal places.
NOWReturns the current system date and time.
FORMATFormats a field as desired for display.

In our journey together through this Knowledge Center, we’ll dive deep into the core aspects of SQL, exploring topics such as basic commands, database relationships and indexing.

Hey, I’m Cristian and since 2017 I helped more than 200,000 students to understand the basics of SQL. You can too with and easy and interactive online SQL tutorial.