Examples of SQL Commands: DDL, DML, DCL, TCL, DQL for IQCode Users

Introduction

This article provides an overview of SQL and its different types of commands. SQL, or Structured Query Language, is a programming language used to manage relational databases.

What is SQL?

SQL is a programming language used to manage and manipulate data in relational databases. It provides a simple and efficient way to handle large amounts of data and retrieve information from multiple sources.

Why do we use SQL?

We use SQL because it is a powerful and efficient way to work with data stored in relational databases. It allows us to access, manipulate and maintain large amounts of data quickly and easily.

Types of SQL Commands

There are five types of SQL commands:

  1. Data Definition Language(DDL)
  2. Data Manipulation Language
  3. Data Control Language(DCL)
  4. Transaction Control Language(TCL)
  5. Data Query Language(DQL)

1. Data Definition Language(DDL)

DDL commands are used to define the structure of a database. They include commands like CREATE, ALTER and DROP, which are used to create, modify and delete tables, indexes, and other database objects.

2. Data Manipulation Language

DML commands are used to manipulate data within a database. They include commands like INSERT, UPDATE and DELETE, which are used to insert, update and delete data from tables.

3. Data Control Language(DCL)

DCL commands are used to control access to data stored in a database. They include commands like GRANT and REVOKE, which are used to grant and revoke privileges to users and roles.

4. Transaction Control Language(TCL)

TCL commands are used to manage transactions within a database. They include commands like COMMIT and ROLLBACK, which are used to commit or undo a group of data manipulations.

5. Data Query Language(DQL)

DQL commands are used to retrieve data from a database. They include commands like SELECT, which is used to select data from one or more tables.

Conclusion

SQL is a powerful programming language used to manage large amounts of data stored in relational databases. Understanding the different types of SQL commands is important for managing and manipulating data efficiently.

FAQS

Here are some frequently asked questions about SQL:

  1. Q.1: What are some of the basic SQL Commands?
  2. Q.2: What is SQL syntax code?
  3. Q.3: How do I write a SQL query?
  4. Q.4: What is DDL in SQL?

Additional Resources

For more information on SQL and its commands, visit:

– https://www.w3schools.com/sql/

– https://docs.microsoft.com/en-us/sql/?view=sql-server-ver15

Overview of SQL Commands in DBMS

SQL is crucial to managing data in databases, making it a fundamental skill for many job positions. In this blog, we will explore the most important SQL commands and statements.

P: SQL, or Structured Query Language, is used to communicate with relational databases. It comes in different types, such as PostgreSQL, MySQL, and Oracle SQL. Knowing SQL is essential for data management in today’s data-reliant world.

Code:
//sample SQL command
SELECT * FROM customers;

//this command retrieves all data from the “customers” table. Other important commands include INSERT, UPDATE, DELETE, and JOIN, which allow for data manipulation and merging.
//It’s important to have a solid understanding of SQL commands and statements when working with databases.

What is SQL?

SQL is the standardized language used for managing and retrieving data from relational databases. It’s the industry standard for database management and is used by popular RDBMS like MySQL, SQL Server, Oracle, Sybase, Postgres, and MS-Access.


// Example SQL query
SELECT * FROM customers WHERE city = 'New York';

SQL allows you to easily interact with and manipulate database data using readable and intuitive commands.

Reasons to use SQL

SQL is widely used for the following reasons:

– SQL provides access to a relational database management system (RDBMS)
– It helps to define and manipulate data
– Users can create, delete and modify databases and tables using SQL statements
– It enables the creation of views, stored procedures and functions in a database
– Users can also configure permissions on tables, processes, and views.

TYPES OF SQL COMMANDS

SQL commands are categorized into five types – DDL, DML, DCL, TCL, and DQL. Let’s discuss each category in detail.

1. DDL (Data Definition Language): This category of SQL commands is used to define or modify relationships and structures in a database. DDL commands include CREATE, ALTER, DROP, RENAME, TRUNCATE, COMMENT, and others.

2. DML (Data Manipulation Language): This category of SQL commands is used to manipulate data stored in a database. DML commands include SELECT, INSERT, UPDATE, DELETE, MERGE, and others.

3. DCL (Data Control Language): This category of SQL commands is used to control access to data in a database. DCL commands include GRANT, REVOKE, and others.

4. TCL (Transaction Control Language): This category of SQL commands is used to manage transactions in a database. TCL commands include COMMIT, ROLLBACK, and others.

5. DQL (Data Query Language): This category of SQL commands is used to retrieve data from a database. DQL commands include SELECT, which is also a DML command.

Note: It’s important to understand the differences between these categories and use the appropriate command for the task at hand.

Understanding DDL in SQL

DDL, or Data Definition Language, in SQL is a set of commands that are used to design the structure of a database. It handles database schema descriptions and the creation, modification, and deletion of the structure of database objects. Examples of DDL commands are CREATE, DROP, ALTER, and TRUNCATE.

One of the first steps to storing data is to establish a database using the CREATE DATABASE statement. For instance:

Code:
CREATE DATABASE db_name;

To build a new database in SQL, replace db_name with the name you wish to give the database.

Next, a table needs to be created to store information, using the CREATE TABLE statement. Tables consist of rows and columns, and it’s important to provide SQL with pertinent information, such as the names of columns, type of data to be stored, and data size. Here is an example:

Code:
CREATE TABLE table_name(
column1 data_type(size),
column2 data_type(size),
column3 data_type(size),
column4 data_type(size),
…..
);

You should replace table_name with the actual name of the table you want to create, column1 with the name of the first column, and so on.

Other important DDL commands include the DROP command, which deletes existing objects in the database, the ALTER command that creates or deletes columns, and the TRUNCATE command that deals with deallocating table extents, effectively deleting data from a table.

Data Manipulation Language

SQL commands that manipulate data in a database are known as Data Manipulation Language (DML). This covers most SQL statements and regulates database access. DCL statements are grouped with DML statements. The DML command does not auto-commit and does not permanently save all database changes, meaning they can be rolled back.

Some common DML commands include:

– INSERT: Inserts data into a table’s row.
Syntax:
INSERT INTO table_name (col1, col2,…colN) VALUES (value1, value2,…valueN)
Or
INSERT INTO table_name VALUES (value1, value2,…valueN)
Example:
INSERT INTO Employee (Emp_Name, DOB, Mobile, Email) VALUES (‘Joe’, ‘1995-02-16’, 7812865845, ‘[email protected]’)

– UPDATE: Updates data in an existing database table.
Syntax:
UPDATE table_name SET column1=value1, column2=value2,… WHERE condition
Example:
UPDATE Employee SET Mobile = 9935467903 WHERE Emp_Name = ‘Joe’

– DELETE: Deletes records from a table.
Syntax:
DELETE FROM table_name WHERE condition
Example:
DELETE FROM Employee WHERE Emp_Name=’Joe’

The above commands are the basics to manage data in SQL.

What is DCL in Database?

Data Control Language (DCL) is a subset of SQL that enables database users to retrieve and modify data stored in databases. DCL includes two main commands: Grant and Revoke.

GRANT COMMAND: This command gives user privileges to access a database. The privileges can include SELECT, INSERT, UPDATE, and DELETE permissions, and may be granted to multiple users and tables.

Syntax: GRANT SELECT, UPDATE ON table_name TO user1, user2;

Example: GRANT INSERT, SELECT on accounts to Alex

This command gives Alex permission to insert into and query the accounts database table.

REVOKE COMMAND: This command is used to take away previously granted permissions from a user. It can revoke default privileges and specific commands like UPDATE and DELETE, and can be used on users, roles, or the public settings.

Syntax: REVOKE privilege_name ON table_name FROM { user_name | PUBLIC | role_name }

Example: REVOKE INSERT, SELECT on accounts from John

This command withdraws John’s permissions to query or insert into the accounts database table.

Transaction Control Language (TCL)

Transaction Control Language (TCL) manages database transactions and handle modifications of data. TCL allows logical grouping of DML statements, which can be committed or rolled back.

TCL commands include:

COMMIT: Saves all transactions in the database.

Syntax: COMMIT;

Example:

“`
UPDATE Employee SET DOB=’1995-02-17′ WHERE Emp_Name=’Joe’;
COMMIT;
“`

ROLLBACK: Reverts all modifications since the last COMMIT or ROLLBACK.

Syntax: ROLLBACK;

Example:

“`
UPDATE Employee SET DOB=’1995-02-17′ WHERE Emp_Name=’Joe’;
ROLLBACK;
“`

SAVEPOINT: Creates a savepoint to rollback transactions to a specific point, instead of undoing the entire transaction.

Syntax: SAVEPOINT SavepointName;

Syntax for roll back to a savepoint command:

ROLLBACK TO SavepointName;

Example:

“`
SAVEPOINT S1; //savepoint created
DELETE FROM Employee WHERE Emp_Name=’Joe’; //deleted
SAVEPOINT S2; //Savepoint created.
“`### Data Query Language (DQL)

DQL is used to query data in schema objects. Its goal is to return a relevant schema relation based on the supplied query. It is a part of SQL that allows you to extract data from a database and organize it using the SELECT statement. When executed, the SELECT statement compiles into a temporary table that can be displayed or used for further actions by the program. To execute a SELECT statement, we need to identify the columns to be included in the result set.

**Syntax:** SELECT expressions FROM Tables WHERE conditions;

**Example:** SELECT Emp_Name FROM Employee WHERE Mobile=9935467903;

This example retrieves the record from the ‘Employee’ table where the mobile number is ‘9935467903’.

Conclusion

In this blog post, we covered the five categories of SQL commands: DCL, DML, DDL, TCL, and DQL. For each command, we provided detailed syntax and examples to help you write queries effectively. SQL commands enable you to create and modify various database objects using different commands. After reading this post, you should be able to use SQL commands with ease and interact with your database effortlessly.

BASIC SQL COMMANDS

SQL commands can be divided into five categories: DDL, DML, DCL, TCL, and DQL. Each category has its own subtypes, which includes:

- CREATE
- INSERT
- DROP
- DELETE
- UPDATE

These are all basic SQL commands.

Understanding SQL Syntax

In SQL, syntax is a set of guidelines that determine the rules and best practices one should follow while creating SQL statements. Almost all SQL statements start with a keyword such as SELECT, INSERT, UPDATE, DELETE, ALTER, DROP, CREATE, USE, SHOW, and end with a semicolon (;).


SELECT column1, column2, ...
FROM table_name;

In the above code, SELECT is the keyword, column1 and column2 are the columns we want to retrieve data from, and table_name is the table we want to query data from. The semicolon at the end indicates the termination of the statement.

Tips for Writing SQL Queries

Writing an efficient SQL query can save you a lot of time and resources. Here are some tips for writing SQL queries:

  • Format the query correctly
  • Specify the SELECT fields instead of using SELECT*
  • Avoid correlated queries when not necessary
  • Limit the results obtained by the query
  • Avoid using DISTINCT clause if possible
  • Avoid using functions in predicates
  • Avoid using AND, OR, or NOT operators
  • Use WHERE clause instead of HAVING

Understanding DDL in SQL

DDL stands for Data Definition Language in SQL. It is a set of SQL commands that are used for describing the database structure. DDL works with database schema definitions and creates and modifies the database object structure. The main purpose of DDL is to create, modify, or delete database structures, but not data. It is recommended that regular users should use an application rather than using DDL commands for accessing the database.

Additional Resources

Here are some useful resources related to SQL:

These resources can help you improve your SQL skills and knowledge.

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