Skip to main content

What Is a Database Schema?


 

A database schema is like a blueprint that defines how data is organized and stored in a database. It describes the structure of tables, columns, data types, relationships, constraints, and indexes, providing a clear framework for how different pieces of data are stored and connected.


🔑 Key Points

  • Schema = Structure → Defines tables, columns, and rules.

  • Ensures consistency → Data must follow the schema (e.g., a column defined as INT cannot store text).

  • Relationships → Specifies how tables connect (foreign keys, primary keys).

  • Constraints → Rules like NOT NULL, UNIQUE, CHECK.


Labels:

Comments

Post a Comment

Our Popular Posts

Oracle Object Oriented Concepts

An Object is a reusable application component that developers need to be aware of, rather than how it works. Object are basic entities in a system. They could represent a person, place, bank account, or any item that is handled by program. Every object consists of an attribute and one or more methods. An attribute could be any property of the object. Class:           It is a collection of attributes and functions (method) to plan the object. Object Table : ·    Object table are created by using the user defined data types. ·        In an object table each row or record is treated as an object. ·        Each row in an object table has an object Identified (OID), which is unique through out       the   database. ·       The rows or objects of an object table can be referenced by other objects with in the  database. ·    ...
Post a Comment
Read more

About Oracle Buffer

About Oracle Buffer :- All Commands of SQL are typed at the SQL prompt. Only one SQL statement is managed in the SQL buffer. The current SQL statement replaces the previous SQL statement in the buffer. The SQL statements can be divided into different lines within the SQL buffer. Only one line i.e, the current line can be active at a time in the SQL buffer. At SQL prompt, editing is possible only in the current SQL buffer line. Every statement of SQL should be terminated using semi colon " ; ". One sql statement can contain only one semi colon. To run the previous or current SQL statement in the bufer type " / " at SQL prompt. To open the SQL editor type " ED " at SQL prompt.
Post a Comment
Read more

Filtering and Sorting data using SQL statements

  Filtering & Sorting Data using SQL     Once you know the basics ( SELECT , FROM , WHERE ), filtering and sorting helps you get the exact rows from tables .   1. Filtering with Conditions ( AND , OR , NOT )  - Use WHERE to filter rows. - Combine with logical operators :     • AND: all conditions true      • OR: any condition true      • NOT: negate condition   - - All conditions true (AND) SELECT *  FROM employees WHERE department = 'Sales'    AND salary > 50000; -- Any condition true (OR) SELECT *  FROM employees WHERE department = 'Sales'     OR department = 'Marketing'; -- Negate condition (NOT) SELECT *  FROM employees WHERE NOT department = 'HR';   2. Pattern Matching with LIKE   - % = any sequence, _ = single char     • Names starting with 'J'      • Names with 4 letters starting with 'J'   - - N...
Post a Comment
Read more

IS NULL Operator

This operator tests for NULL values. It is the only operator that can be used to test for NULL’s. The negation is IS NOT NULL.       Examples :-        Select ename, deptno, comm from emp where comm IS NULL;         Select ename, deptno, comm from emp where comm IS NOT NULL;         Select ename, deptno, job, mgr from emp where mgr IS NULL;         Select ename, deptno, job, mgr from emp where mgr IS NOT NULL; HOME
Post a Comment
Read more

Introduction to SQL

INTRODUCTION : - SQL usually pronounced as “Sequel” stands for Structured Query Language. SQL is the native language of the Oracle Server. It is the language used to communicate with the database. Again SQL consists of SQL statements and SQL*Plus commands. SQL statements are used to talk to the database. When you enter a SQL statement, it is stored in a part of the memory called the SQL Buffer and remains there until a new statement is entered. SQL*Plus is an Oracle tool that recognizes and submits  SQL statements to the Oracle server for execution and contains its own command language. Features of SQL:- It is very easy to write, it can be used by all kinds of users with little or not programming experience. It is a non-procedural language. It reduces the amount of time required for creating and maintaining systems. It is based on American National Standards Iinstitute (ANSI) standard SQL. It manipulates data and ...
Post a Comment
Read more

The "Dual Table" in Oracle

> The " DUAL " table is a one row and one column table. The owner of this table is "SYS" but it's accessible to all the db users.  > It is having single column called as " DUMMY " > It is used to test SQL expression with out querying to the main/real tables.  Eg : 1> SELECT SYSDATE FROM DUAL; O.P : It will print current date and time.       2> SELECT 'Hello, Welcome to SQL' from DUAL; O.P :  3> SELECT 5*9 AS RESULT FROM DUAL; O.P:  #SQL #LEARNSQL #DUALTABLE
Post a Comment
Read more

LIKE operator in ORACLE

Wild Charcters :- These characters are used to provide pattern matching which means comparision to data is provided with partial value. ORACLE provides the following wild characters.            i)      _(Underscore) -> Represents single character.             ii)      %(Percentage) -> Represents group of character. Ø   Inorder to have wild characters for the comparision to partial data, LIKE operator is used. Ø   If these wild characters are formed in data, then the wild characters can be converted to data using ‘\’ (backslash). It is represented through an option called ‘ESCAPE’ , which is written after like operator. Examples :- Display employee number and employee name of all those employees whose names contain 4 characters. Ans : select empno, ename from emp           Where ename LIKE ‘---...
Post a Comment
Read more

List Of Table Operations in SQL

  List of Table Operations in SQL [ 1. CREATE , 2. INSERT , 3. UPDATE , 4. ALTER , 5. DELETE , 6. DROP , 7. TRUNCATE ] 1.      CREATE : To define a new Table. 2.     INSERT : Add rows to the table. 3.     UPDATE : Modify existing rows in the table. 4.     ALTER : Modify the structure of the table. 5.     DELETE : Remove Rows from the table. 6.     DROP : Removes the entire table. 7.     TRUNCATE : Removes the all rows of the table but it keeps the table structure. 1>       CREATE : To define a new Table.   CREATE TABLE jobs (     job_id INT PRIMARY KEY ,     job_title VARCHAR (100),     job_description TEXT ,     min_salary DECIMAL (10, 2),     max_salary DECIMAL(10, 2) ...
Post a Comment
Read more