SQL Commands with Examples in Oracle
SQL Commands with Examples in Oracle is our topic in this post. Our idea in the post SQL Commands with Examples in Oracle is to give some hands on practice to readers of this post.
SQL- STRUCTURED QUERY LANGUAGE
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| sql commands with examples in oracle |
SQL stands for structured query language. SQL is a non procedural language. Non procedural languages are those languages in which stress is given on what to do, not on how to do. SQL is popular from last few decades. SQL is basically a tool for creating database objects, dropping database objects, tool for data manipulation operations.
Based on various operations performed by SQL, it can be divided into following components
DDL Data definition Language
DML Data manipulation Language
DCL Data control Language
QL Query Language
DDL- Data definition Language
In Data definition Language part of SQL , new database objects can be created, existing data base objects can be dropped. We can also alter database objects in this part of SQL.
We can create a table in SQL using Create table command. By using Drop table command , existing table can be dropped. We can add new columns in existing tables using Alter Table command.
In Data manipulation Language, we can perform various data manipulation operations on database objects. We can insert records in the tables, we can delete records from database and we can update records of the tables. To insert new records or rows, Insert command can be used. For deletion of records from database tables, Delete command can be used. To update records of table, Update table command can be used.
DCL Data control Language
In Data control Language part of SQL, new users can be created. We can Grant privileges to the users and also can revoke privileges from the users. For creating new users, we can use Create User command can be used. For grating privileges to the users, Grant command can be used.
Transactions can also be controlled in this part of SQL. Transactions can be controlled using Rollback and commit commands of SQL.
It is most popular components of SQL. In this component of SQL we can query from database objects. For querying, Select From Where clause can be used.
DDL Data definition Language
In Data definition Language part of SQL , new database objects can be created, existing data base objects can be dropped. We can also alter database objects in this part of SQL.
We can create a table in SQL using Create table command. By using Drop table command , existing table can be dropped. We can add new columns in existing tables using Alter Table command.
Create Table Command
Lets us create a table named employee, let this table have three columns namely ecode, ename and ecity.
SQL> Create table employee( ecode char(4),ename varchar2(20), ecity varchar2(2));
This will create table employee in database. In this way you can create any table
Drop Table Command
We can drop an existing table in SQL, by using Drop Table Command.
The general syntax of Drop Table command is as given below
SQL> Drop table employee;
Adding New Columns using Alter Table command.
Suppose we want to add zipcode column in employee table.
This will add a new column zipcode to employee table.
Modifying existing columns of a table
The general syntax for modifying existing columns is given below
Alter table tablename modify( column new_specification);
SQL>Alter Table employee modify( ecode char(6));
Note: Be careful while changing column specifications
