What is Primary Key and Foreign Key

14 Jun by dbtut Tags: , , , , , , , , , , ,

What is Primary Key and Foreign Key

  Primary Keys ensures that records in the table are unique. When you create a primary key on a column, a value entered into that column can not be re-entered for the next future insert. For example, you put a primary key in the ID column and set the value of 1 for your first […]
13 Jun by dbtut Tags: , , , , , , , , , , , , , , , , ,

Statistic Concept and Performance Effect on SQL Server

  We will talk about statistic concept in this article. In the article “Index Concept and Performance Effect on SQL Server” we mentioned how index will affect the performance of a query. When a query arrives at SQL Server, SQL Server decides how the query will work. It benefits from statistics when deciding how the […]
13 Jun by dbtut Tags: , , , , , , , , , , , , , , ,

How To Fix Block Corruption On Oracle

  In this article, we will see how to fix block corruption when there is a block corruption on a data file. If Block Corruption is on the index, you can solve the problem by dropping and recreating the index. In some cases, block corruption can also be on free pages. We connect to the […]
12 Jun by dbtut Tags: , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , ,

Index Concept and Performance Effect on SQL Server

  Indexes allow us to access data faster and with less reading. As a concrete example, if you do not have a catalog page in a book, consider how you will find what you are looking for in the book. You need to read the entire book from start to finish. In order to find […]
11 Jun by dbtut Tags: , , , , , , , , , ,

What is Vacuum On PostgreSQL

  When a delete operation is performed in Postgres, the deleted data is not deleted directly from the disk. The visibility of the rows disappears. Vacuum puts a pointer to the visibility mapping. This pointer shows the block which the data was deleted from which block. It then actually deletes the rows in the visibility […]
11 Jun by dbtut Tags: , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , ,

How To Install PostgreSQL Replication On Centos

First we go to https://yum.postgresql.org and into PostgreSQL where we will download the repo. Since we will use PostgreSQL 10 in our example, we will click on 10.   Then right click on “Centos 7 – x86_64” in the screen below and we click copy link location.   We connect to our Centos server via […]
10 Jun by dbtut Tags: , , , , , , , , , , , , , , , , , , , , ,

Difference Between Clustered Index and Non Clustered Index

  To better understand this article, I would first recommend reading the “Index Concept and Performance Effect on SQL Server” and “Statistics Concept and Performance Effect on SQL Server” articles. In these two articles, the concepts of Index and statistics are explained in detail. You can see the Clustered Index and Non Clustered Index differences […]