Oracle 11g introduced the concept of 'Virtual Column' within a table. Virtual Columns are similar to normal table's columns but with the following differences:They are defined by an expression. The result of evaluation of this expression becomes the value of the column. The values of the virtual column are not stored in the database. Rather, it's computed ...
Aggregate functions return a single result row based on a group of rows. This differentiates them from Single-Row functions which act on each row. These functions are extensively used with the GROUP BY clause in SQL statements. AVG (), COUNT (), SUM () ... are few aggregate functions which are quite commonly used. Today, one ...
Most of the times, production data is not available in development environments. Here, I would like to share a single sql command which can generate random data. But before that, let's address another issue faced by a lot of new oracle users. We need to generate a sequence of numbers using a sql statement. This will generate a number sequence. ...
Deleting duplicate rows from tables is one of the common task oracle developers come across. The data might get duplicated because of missing primary/unique key on the table or batch file getting loaded multiple times. Here I have tried to summarize different ways of deleting this duplicated data. Please note that this is not an extensive list ...
The effective usage of an index is always a big question. There are instances in production environments, where an index may help the performance of just a single query, while it can degrade the performance of a number of queries. Always the Optimizer can’t guarantee the best suitable index required for the query in an environment ...
As the data grows in relational databases (new business requirements, managing audit data etc), the cost associated with the disk systems to store that data and the resources required to manage them becomes vital. Oracle understands this requirement and it is continuously implementing and improving on the compression techniques and algorithms while simultaneously meeting the application scalability ...
The Primary Key(PK) constraint is the most basic concept of any RDBMS (I am particularly interested in Oracle). Yet, I have noticed people getting confused when it comes to the practical usage and asking questions like:- I have disabled PK and now oracle is doing full table scan. - How PK constraints and indexes are related/different? - How ...
Although I work mainly in Java/J2EE, recently I had a requirement in Oracle to take temporary backup of a table and compare the data of original table with this backup table. So I had to copy the data from table A to a temp table TA.First I tried creating temp table normally and copied the ...
