SQL Basics

What is SQL?

SQL stands for Structured Query Language and lets you access and manipulate databases. It is an ANSI (American National Standards Institute) standard.

SQL lets you

create new databases
delete databases
insert records in a database
update records in a database
delete records from a database
execute queries against a database
retrieve data from a database
create new tables in a database
create stored procedures in a database
create views in a database
insert records in a table
update records in a table
delete records from a table
delete tables
set permissions on tables, procedures, and views

SQL Extensions

Several DBMS vendors have expanded the capabilities of SQL by introducing new statements or instructions to the language. These extensions serve the purpose of enhancing functionality or simplifying specific operations. While these extensions can be highly beneficial, they are often specific to a particular DBMS and are typically not supported by multiple vendors. On the other hand, the standard SQL governed by ANSI committee, is commonly referred to as ANSI SQL. It is noteworthy that all major DBMSs, including those with their own extensions, support ANSI SQL as a common standard.

SQL Statements

An SQL statement is a command or instruction written in the Structured Query Language (SQL) to perform a specific action on a database. SQL statements are used to interact with databases by retrieving, manipulating, or managing data stored in them.

There are several types of SQL statements, including:

Data Manipulation Language (DML) statements: These statements are used to retrieve, insert, update, and delete data from a database. Examples include SELECT, INSERT, UPDATE, and DELETE.
Data Definition Language (DDL) statements: DDL statements are used to define or modify the structure and schema of database objects such as tables, indexes, and constraints. Examples include CREATE, ALTER, and DROP.
Data Control Language (DCL) statements: DCL statements are used to control access permissions and security settings in a database. Examples include GRANT and REVOKE.
Transaction Control Language (TCL) statements: TCL statements are used to manage transactions within a database. Examples include COMMIT, ROLLBACK, and SAVEPOINT.

Keywords

SQL statements are made up of one or more English terms, called keywords. For example CREATE, SELECT, INSERT INTO, GRANT are only a few of the statements. Columns or tables should never be named using a keyword.

Clauses

Clauses are keywords and/or built-in functions that help fetch the records from a table. A clause is used with a conditional expression, i.e. a threshold number to limit the number of rows being displayed (LIMIT 20) or column(s) to perfom aggragration (GROUP BY year). Some of the widely used clauses including.

CONSTRAINT clause
FROM clause
WHERE clause
GROUP BY clause
HAVING clause
ORDER BY clause
WITH clause
USING clause
LIMIT clause
OFFSET clause
AND / OR clause

Do not use clauses to name a column or field!

Last updated 3 months ago

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SQL lets you

create new databases

delete databases

insert records in a database

update records in a database

delete records from a database

execute queries against a database

retrieve data from a database

create new tables in a database

create stored procedures in a database

create views in a database

insert records in a table

update records in a table

delete records from a table

delete tables

set permissions on tables, procedures, and views

SQL Extensions

SQL Statements

There are several types of SQL statements, including:

Data Manipulation Language (DML) statements: These statements are used to retrieve, insert, update, and delete data from a database. Examples include SELECT, INSERT, UPDATE, and DELETE.

Data Definition Language (DDL) statements: DDL statements are used to define or modify the structure and schema of database objects such as tables, indexes, and constraints. Examples include CREATE, ALTER, and DROP.

Data Control Language (DCL) statements: DCL statements are used to control access permissions and security settings in a database. Examples include GRANT and REVOKE.

Transaction Control Language (TCL) statements: TCL statements are used to manage transactions within a database. Examples include COMMIT, ROLLBACK, and SAVEPOINT.

Clauses

CONSTRAINT clause

FROM clause

WHERE clause

GROUP BY clause

HAVING clause

ORDER BY clause

WITH clause

USING clause

LIMIT clause

OFFSET clause

AND / OR clause

Do not use clauses to name a column or field!