Technical Interview Questions and Answers :: iGate

A data base schema which is specified by a set of definitions expressed by a special language is called DDL. Data Definition Language (DDL) is used to define and manage all the objects in an SQL database.

It is a special language used to manipulate the Data. Data Manipulation Language (DML), which is used to select, insert, update, and delete data in the objects defined using DDL.

The PRIMARY KEY is the column(s) used to uniquely identify each row of a table.

A FOREIGN KEY is one or more columns whose values are based on the PRIMARY or CANDITATE KEY values from the database.

A UNIQUE KEY is one or more columns that must be unique for each row of the table.

The UNIQUE KEY column restricts entry of duplicate values but entry of NULL value is allowed. In case of PRIMARY KEY columns entry of duplicate as well as value is also restricted.

A View is a database object that is a logical representation of a table. It is derived from a table but has no storage space of its own and often may be used in the same manner as a table.

ROWID is the logical address of a row, and it is unique within the database.

INDEX is a general term for an SQL feature used primarily to speed up execution and impose UNIQUENESS upon data. You can use an index to gain fast access to specific information in a database table. An index is a structure that orders the values of one or more columns in a database table. The index provides pointers to the data values stored in specified columns of the table, and then orders those pointers according to the sort order you specify.

: An entity that maps over a result set and establishes a position on a single row within the result set. After the cursor is positioned on a row, operations can be performed on that row, or on a block of rows starting at that position. The most common operation is to fetch (retrieve) the current row or block of rows.