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:
- Creation of a database (CREATE DATABASE).
- Creating a table (CREATE TABLE)
- Creation of a view (CREATE VIEW)
- Creating a table index (CREATE INDEX)
- Creating a stored procedure (CREATE PROCEDURE)
- Creating triggers (CREATE TRIGGER)
- Query data stored in a table (SELECT)
- Inserting data into a table (INSERT)
- Modifying existing data in a table (UPDATE)
- Delete data stored in a table (DELETE)
- Give access permission to data in a table (GRANT)
- Remove access permissions to data in a table (REVOKE)
- End the transaction of a SQL statement (COMMIT)
- Roll back the transaction of a SQL statement (ROLLBACK).
SQL Advanced
- SQL TOP
- SQL LIKE
- SQL WILDCARDS
- SQL IN
- SQL BETWEEN
- SQL ALIAS
- SQL JOINS
- SQL INNER JOIN
- SQL LEFT JOIN
- SQL RIGHT JOIN
- SQL FULL JOIN
- SQL UNION
- SQL SELECT INTO
- SQL CREATE DATABASE
- SQL CREATE TABLE
- SQL CONSTRAINTS
- SQL NULL
- SQL NOT NULL
- SQL UNIQUE
- SQL UNIQUE ALTER TABLE
- SQL PRIMARY KEY
- SQL FOREIGN KEY
- SQL CHECK
- SQL DEFAULT
- SQL CREATE INDEX
- SQL DROP
- SQL TRUNCATE
- SQL ALTER
- SQL AUTO INCREMENT
- SQL VIEWS
- SQL DATES
SQL Functions
SQL has predefined functions to perform certain calculations with higher performance.
| AVG | Returns the average value of a column. |
| COUNT | Returns the number of rows in the query. |
| FIRST | Returns the first value of the query. |
| LAST | Returns the last value of the query. |
| MAX | Returns the largest value in a column. |
| MIN | Returns the smallest value in a column. |
| SUM | Returns the sum of the values in a column. |
| GROUP BY | Group rows with the same value in a column. |
| HAVING | Include conditions with SQL functions. |
| UCASE | Convert a value to uppercase. |
| LCASE | Convert a value to lowercase. |
| MID | Extracts characters from a text field. |
| LEN | Returns the length of a text field. |
| ROUND | Rounds a numeric field to a specified number of decimal places. |
| NOW | Returns the current system date and time. |
| FORMAT | Formats a field as desired for display. |
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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.
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