what is the difference between primary key & foreign key?

Primary keys enforce entity integrity by uniquely identifying entity instances. Foreign keys enforce referential integrity by completing an association between two entities.

What is the difference between SQL, DDL, and DML?

Structured Query Language (SQL) is a language that provides an interface to relational database systems. In common usage SQL also encompasses DML (Data Manipulation Language), for INSERTs, UPDATEs, DELETEs and DDL (Data Definition Language),

find out the third highest salary?

select sal from emp where sal=(select min(sal) from emp where sal>(select min(sal) from emp where sal>(select min(sal) from emp);

Difference between primary key and unique key ?

The column holding the primary key constraint cannot accept null values.whereas colum holding the unique constraint can accept null values assume that t3 is a table with two columns t1 having primary key constraint and t2 having unique constr

In Oracle 9i what does "i" Stands for?

It is an advanced version of Oracle 8 for Internet-based applications. Hence here in Oracle9i i stands for Internet.

What are joins..how many types of joins are there?

Joins are used to fetch a query on more than one table. You can broadly catagorize joins in to four types. 1. Equi Join 2.Non Equijoin 3.outer joins 4.self joins

Difference between sub query and nested query ?

Hi Friends, Query inside a query is called as Sub query. Sub query is also called as Nested Query. Thanks REDDY

What is Normalization ?

It is a technique for designing a database system. (BEST OF LUCK)

What is the difference between column level constraints and table le

Column level constraints are applicable to that column only, whereas table level conatraints are used to define composite keys like primary key for the combination of two or more columns in a table

Query to get max and second max in oracle in one query ?

select distinct(a.colname) from table a where &n=(select count(distinct(b.colname)) from table b where a.colname<=b.colname); from this query u can find out Nth MAX in a one query eg select distinct(a.sal) from emp a where &n=(

Can we create index on views?

An index cannot be defined on a view. Because view is virtual table, which consists of a subset of columns from one more tables. The Restrictions imposed on views are as follows: 1. A view can be created only in the current database. 2. A vi

what are indexes..how many types of index's are there and what a

when queries are run against a DB,an index on that DB basically helps in the way the data is sorted to process the query for faster data retievals. There are basically two types of indexes that we use in SQL Server. Clustered and the Non-Clu

which sql command we can use to get a print out from oracle?

set autoprint off/on it is Sql*plus Command

find out the second highest salary?

select max(sal) from emp where sal < select max (sal)from emp Mallikarjun

What is TNS File

TNS stands for TRANSPARENT NETWORK SUBSTRATE. it is sql*net configuration file that defines datbases address for establishing connection to them.

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