ABSTRACT OF THE TOPIC
It is the standard language for accessing and manipulating a database. So the primary use of structured query language is to access and manage the database. All the Relational database management system such as My SQL, SQL Server, and Oracle etc. uses SQL as their standard database language.
IMPORTANCE OF SQL
It is mainly used to perform many queries in a database. Queries are as follows:
- Used for executing queries against a database.
- Used for retrieving data from a database.
- Used for inserting records in the database.
- Used for updating a record in the database.
- Used for deleting a record in the database.
- To create a new database.
- To create a new table in the database.
- To establish stored procedures in the database.
- To create views in the database.
- It also has a set of permission on tables, procedures and views.
There are many commands used in the query language. Some of the commands such as create, select, insert, update, delete and drop etc. These commands can be classified based on their nature (means what type of language we are using which is wholly based on the user requirement).
So different languages that are used in SQL commands are:
- DDL: Data Definition Language.
- DML: Data Manipulation Language.
- DCL: Data Control Language.
So complete SQL commands are divided into the above three types.
- Introduction of DDL: It is used for defining and modifying the data and its structure. It is used to build and change the structure of your tables and also other objects in the database.
Commands used in DDL are Create, Drop, Alter, Rename, and Truncate.
Create: It is used for creating objects in the database and create a new table.
Create table employee
city char (30),
phone no varchar (15).
DROP: It allows us to remove the entire database object from the database. It deletes a table, index or views.
Drop table employee;
Drop database employee;
Delete: If you want to remove individual records then use DELETE command of DML statement.
ALTER: It allows to alter or modify the structure of the database and add additional columns also drops existing columns and even change data types of columns.
Alter table employee Add (address varchar (25));
Alter table employee change
(Phone no)(Contact no);
Alter table employee drop column of empname;
To view change structure of the table using 'DESCRIBE' command.
DESCRIBE table employee;
It is used to rename an object and a database table.
Rename table employee to EMP;
It is used to delete the entire rows from the table permanently.
This command is same as delete but the only difference is Truncate command does not generate any rollback data whereas Delete does.
Truncate table employee;
- Introduction to DML:The primary use of DML is for selecting, inserting, deleting and updating data in the database. So to manipulate a database weneed to choose to delete insert or update. It is used to retrieve and manipulate data in the database. DML performs only read-only queries of data.
It is used to retrieve data from the database with the help of clauses. Clauses such as WHERE: which row to retrieve,
GROUPBY: arrange data into a group.
HAVING: select among the group by clauses.
ORDER BY: specifies the order.
AS: provides alias or rename tables.
For example or syntax:
Select * from <table name>;
It is used for inserting data into a table; you can add one or more records into a single table.
Insert into <table name>
Values ('value1','value 2','value n');
It modifies the records present in the existing table.
Update<table name> set<column name = value> where condition.
Update emp set salary = 200000 where ename = 'Pawan';
It is used to delete some or all records from the existing table.
DELETE from<table name>where <condition>
- Introduction to DCL:The primary use of DCL is to control user access in a database, related to security issues. It allows restricting the user from accessing data in the database schema. Command used are GRANT which gives the permission (access privileges to the database) and REVOKE means releasing the command.
GRANT: It gives user access privileges to the database.
GRANT<privileges list > ON<relation name or view name> TO<user/role list>;
GRANT ALL ON emp to ABC;
REVOKE: It is used to cancel previously or granted or denied permissions.
So with the help of revoke command granted would be released and released would be allowed.
ON<relation name or view name>
From <user name>
REVOKE update ON employee from ABC;
TOPICS COVERED UNDER SQL ASSIGNMENT HELP BY MYWORDSOLUTIONS
The SQL Assignment Help service by Mywordsolutions covers every topic from basic SQL to advanced SQL. Our all-rounder experts proffer all your SQL assignment questions along with their solutions in simple words or language. SQL is somewhat a topic which has simple queries to complex queries. The topics in SQL subject includes the following:
- DDL: Data Definition Language
- DML: Data Manipulation Language
- DCL: Data Control Language
- DQL: Data Query Language
Features, definition, and description of a structured query language
Constraints in SQL:
- not null
- primary key
- foreign key
- Index etc.
- Concepts of fields and records
Concepts of fields and records
Create, drop, rename, delete, truncate, copy, and alter tables
Create, drop, rename, and select from a database
Where, and, or, with, as, order by, having, group by
Select, insert, update, delete
Inner, outer, full, and cross join
Arithmetic, logic, and comparison operators
Commit, rollback, and save point
Boolean, numeric and date expressions
Truncate, char, replace, reverse, substring etc.
Sub-queries in SQL
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