What is Meant by Key in SQL?

Key in SQL can be defined as the subset of the columns present in tables which permit to uniquely identify a row. Every row in a table will have unique value for key. Keys are used to fetch records from a table according to the given condition. The different types of key used to retrieve […]

What is Meant by Inner and Outer Joins?

Joins in SQL are used to return rows by combining and comparing different tables present in a database. Joins are classified into two types: Inner Join Outer Join Inner Join Inner Join is used to find the similarities between two tables present in a database. Inner Join searches for overlapping data in a table. If […]

What is Meant by Database Index?

Database indexes in SQL, allows the developer to quickly retrieve the data from a database. The searching process in a database can be accelerated using database indexes. A database index is a copy of key values stored in a table. If database index is not used, then every query will scan the entire table to […]

What is Lock Escalation?

Lock escalation is the process of increasing the levels of database locks. Lock escalation is supported by popular databases like SQL Server, SyBase and DB2. In DB2, the parameters like ALTER TABLESPACE and LOCKMAX of CREATE TABLESPACE are used to control lock escalation. Read: SQL Database Deadlock What is the purpose of lock escalation? The […]

What is DISTINCT in SQL?

The Distinct keyword in SQL is used to prevent duplication of data in SQL. Distinct keyword is mostly used check whether a particular record is present in a table. In a SQL code, the use of DISTINCT keyword is allowed only once. However number of columns specified in a SELECT DISTINCT statement is not restricted. […]

What is Database Transaction?

Database transaction can be defined as the separate actions which are in either processed or yet to be processed state. All or Nothing is the defining feature of a database transaction. Each and every database transaction will contain several SQL statements. The common database transaction scenario can be noted using the acronym ACID. How to […]

What is Database Locking?

Database lock can be used to restrict the access certain data to some particular user/session. The database locking is most commonly used to prevent updating same data by two or more different users. Database locking are usually done using ROLLBACK or COMMIT SQL statements. When a user/session is updating a data; it will be kept […]

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