SQL injection can be defined as the process of a hacker trying to inject malicious SQL code inside your database. Installing malicious SQL code will force your database to run according to the commands generated by the malicious code. The process of injecting malicious SQL code is also known as malicious payload. SQL injection is […]
What is Self Join?
The process of joining two sets of data present in a table and displaying the resultant data in a new table is called as self join. If a data present in a table has NULL value, it will be omitted in the resultant table. A duplicate copy of a table will be created before a […]
What is Selectivity? How to Calculate Selectivity?
The terms Data cardinality and Selectivity are quite similar in their operations and many novice SQL developers confuse between these terms. Selectivity can be defined as the ratio between number of rows and cardinality of the table. The selectivity which returns the most post possible rows can be termed as “bad selectivity” whilst the selectivity […]
What is Secondary Key?
The questions about secondary key in SQL is common in most database interviews. The Candidate keys which are not selected as primary key is classified as Secondary key. Consider that you have a table, there will be several keys in a table which can be selected as a primary key. The keys which has the […]
What is Referential Integrity?
Referential integrity in RDBMS can be defined as a consistent relationship shared between tables present in a database. In other words, the foreign key references used in a database must agree with the references of primary key. The set of referential integrity constraints can applied to foreign key to prevent a row from entering inside […]
What is Oracle Transaction?
The logical work piece which consist two or more statements is called as a transaction. The transactions are started by reading or writing a data. It is ended by COMMIT or ROLLBACK of the statements. The commits which are performed first by the DDL statements are called as implicit commits. Multiversion concurrency and transaction locking […]
What is Natural Key?
Natural key can be defined as an identifier of row which is composed of data. The data present in the database will describe according to its attributes. The row identifier in a database is the focal point of clustered and nonclustered indexes. What is Cost Based Optimizer? Why it is called as Natural key? Consider […]
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