Basics of SQL

Question

 SQL (Structured Query Language) is a standardized programming language used for managing relational databases and performing various operations on the data in them. Initially created in the 1970s, SQL is regularly used by database administrators, as well as by developers writing data integration scripts and data analysts looking to set up and run analytical queries.

RDBMS stands for Relational Database Management System. RDBMS is the basis for SQL, and for all modern database systems such as MS SQL Server, IBM DB2, Oracle, MySQL, and Microsoft Access. The data in RDBMS is stored in database objects called tables. A table is a collection of related data entries and it consists of columns and rows.

SQL commands are divided into several different types, among them data manipulation language (DML) and data definition language (DDL) statements, transaction controls and security measures. 

                        

Some of The Most Important SQL Commands:

• SELECT - The SELECT statement is used to select data from a database. 

          Syntax: SELECT column1, column2, ...
          FROM table_name;

          SELECT * FROM table_name;

• UPDATE - The UPDATE statement is used to modify the existing records in a table.

         Syntax: UPDATE table_name
         SET column1 = value1, column2 = value2, ...
         WHERE condition;

• DELETE – The DELETE statement is used to delete existing records in a table.

          Syntax: DELETE FROM table_name
          WHERE condition;

• INSERT INTO - The INSERT INTO statement is used to insert new records in a table.

          Syntax: INSERT INTO table_name (column1, column2, column3, ...)
          VALUES (value1, value2, value3, ...);

• CREATE DATABASE - creates a new database

          Syntax: create database database_name;

• CREATE TABLE – The CREATE TABLE statement is used to create a new table in a database.

          Syntax:

          CREATE TABLE table_name (
          column1 datatype,
          column2 datatype,
          column3 datatype,
           ....
           );

• ALTER TABLE - The ALTER TABLE statement is used to add, delete, or modify columns in an existing table.

          Syntax:

          ALTER TABLE table_name
          ADD column_name datatype;

• DROP TABLE - The DROP TABLE statement is used to drop an existing table in a database.

          Syntax: DROP TABLE table_name;

• CREATE INDEX - The CREATE INDEX statement is used to create indexes in tables.

          Syntax: CREATE INDEX index_name
          ON table_name (column1, column2, ...);

• DROP INDEX - The DROP INDEX statement is used to delete an index in a table.

          Syntax: DROP INDEX table_name.index_name; 

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