Permissions
There is a need for an access control mechanism implemented in a multi-user environment. You have to be able to control who can access what. Thus Oracle implemented privileges to …
Permissions Read MoreSQL Basic
DDL Statements
DDL (stands for Data Definition Language) statements are used for objects creation. I might write a book on this topic because there are many different objects in a database and …
DDL Statements Read MoreDML statements
DML (stands for Data Manipulation Language) statements are used to manipulate (add, delete, modify) data. They support transactions. What is a transaction? It means that no matter what changes you …
DML statements Read MoreSet Operators & Compound Queries
Set operators are used to combine multiple queries together. We call such queries “compound queries”. All set operators have the same precedence unless parentheses are usedYou can only combine queries …
Set Operators & Compound Queries Read MoreSubqueries
Subqueries come in handy when it comes to a complex logic. There are many cases where it is easier to tackle the problem using subqueries. Let me start with an …
Subqueries Read MoreDisplaying Data From Multiple Tables
The solution for the need of data extraction from multiple tables, whether it is for a purpose of comparison or to display them together, lies in JOINs. There are three …
Displaying Data From Multiple Tables Read MoreData Aggregation Using GROUP BY
Anytime you need to aggregate some data you have to define two things: what are the dimensions what are the facts First of all, what is a dimension and what …
Data Aggregation Using GROUP BY Read MoreConditional Expressions
In any programming or scripting language, we have to implement a decision logic. SQL is no different and Oracle comes with two easy directives how to handle it; they are …
Conditional Expressions Read MoreSingle-Row Functions
These functions return a value for each record for a queried table or a view. There are 7 main categories listed below. Numeric Character returning number returning character Date / Date …
Single-Row Functions Read MoreRestricting and Sorting Data
In order to customize your data selection, you might be needing to restrict / filter out some data and sort / order them. To do so, you need to use …
Restricting and Sorting Data Read MoreSELECT statement (decomposed)
The most commonly used and basic type of SQL (stands for Structured Query Language) is a SELECT statement. SELECT With the SELECT statement, we can retrieve data from a table. …
SELECT statement (decomposed) Read MoreNULL
What is NULL? NULL values have a special function. They represent nothing 🙂 Anytime you see NULL in a table that means there is nothing. Blank space, zero and NULL …
NULL Read MoreDatabase Objects
Database objects relate to schema and non-schema objects. Schema objects – a collection of logical structures of data related to a schema Clusters A cluster is an object that contains data …
Database Objects Read MoreUser, Schema and Role
In order to maintain security in a multi-user environment, you have to define different access types for different users. Many people wonder what is the difference between a user and …
User, Schema and Role Read MoreDatabase Design: ERD, NFs
All projects start with a design. Polished database design is necessary to have a successful business. Even if your queries are optimized and tuned to perfection you will not be able to …
Database Design: ERD, NFs Read MoreDBMS and Other Relational Models
DataBase Management System (DBMS) controls the storage, management/organization, and retrieval of data. DBMS consists of three major parts: Kernel code Data dictionary (metadata) Query language The most widely known and used …
DBMS and Other Relational Models Read More