Database General Interview Questions
1.
What
is normalization
Well
a relational database is basically composed of tables that contain related
data. So the Process of organizing this data into tables is actually referred
to as normalization.
2.
What
is a Stored Procedure
Its
nothing but a set of T-SQL statements combined to perform a single task of
several tasks. Its basically like a Macro so when you invoke the Stored
procedure, you actually run a set of statements.
3.
Can
you give an example of Stored Procedure ?
sp_helpdb
, sp_who2, sp_renamedb are a set of system defined stored procedures. We can
also have user defined stored procedures which can be called in similar way.
4.
What
is a trigger?
Triggers
are basically used to implement business rules. Triggers is also similar to
stored procedures. The difference is that it can be activated when data is
added or edited or deleted from a table in a database.
5.
What
is a view?
If
we have several tables in a db and we want to view only specific columns from
specific tables we can go for views. It would also suffice the needs of
security some times allowing specfic users to see only specific columns based
on the permission that we can configure on the view. Views also reduce the
effort that is required for writing queries to access specific columns every
time.
6.
What
is an Index?
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 and data retrievals are much
faster when we have an index.
7.
What
is the basic difference between clustered and a non-clustered index?
The
difference is that, Clustered index is unique for any given table and we can
have only one clustered index on a table. The leaf level of a clustered index
is the actual data and the data is resorted in case of clustered index. Whereas
in case of non-clustered index the leaf level is actually a pointer to the data
in rows so we can have as many non-clustered indexes as we can on the db.
8.
What
are cursors?
Well
cursors help us to do an operation on a set of data that we retreive by
commands such as Select columns from table. For example : If we have duplicate
records in a table we can remove it by declaring a cursor which would check the
records during retreival one by one and remove rows which have duplicate
values.
9.
Can
you tell the difference between DELETE & TRUNCATE commands?
Delete
command removes the rows from a table based on the condition that we provide
with a WHERE clause. Truncate will actually remove all the rows from a table
and there will be no data in the table after we run the truncate command.
10.
Can
we use Truncate command on a table which is referenced by FOREIGN KEY?
No.
We cannot use Truncate command on a table with Foreign Key because of
referential integrity.
11.
What
is the difference between a HAVING CLAUSE and a WHERE CLAUSE?
Having
Clause is basically used only with the GROUP BY function in a query. WHERE
Clause is applied to each row before they are part of the GROUP BY function in
a query.
12.
What
do you mean by COLLATION?
Collation
is basically the sort order. There are three types of sort order Dictionary
case sensitive, Dictonary - case insensitive and Binary.
13.
What
are Joins ?
Join
actually puts data from two or more tables into a single result set.
14.
Can
you explain the types of Joins that we can have with Sql Server?
There
are three types of joins: Inner Join, Outer Join, Cross Join
15.
What
is difference between UNIQUE and PRIMARY KEY constraints?
Both
are Constraints and both creates an index on the specified columns.
UNIQUE is a constraint which enforces distinct column values on a table column and can contain a NULL record also.
PRIMARY KEY is a constraint similar to UNIQUE, however it cannot have a Null value for the column. Moreover a PRIMARY KEY can be the parent column for a Parent - Child relationship(Foreign Key).
UNIQUE is a constraint which enforces distinct column values on a table column and can contain a NULL record also.
PRIMARY KEY is a constraint similar to UNIQUE, however it cannot have a Null value for the column. Moreover a PRIMARY KEY can be the parent column for a Parent - Child relationship(Foreign Key).
16.
What
is a OUTER JOIN?
An
OUTER JOIN returns all rows that satisfy the join condition and also returns
some or all of those rows from one table for which no rows from the other
satisfy the join condition.
17.
When
do you use WHERE clause and when do you use HAVING clause?
The
WHERE condition lets you restrict the rows selected to those that satisfy one
or more conditions. Use the HAVING clause to restrict the groups of returned
rows to those groups for which the specified condition is TRUE.
18.
What
is difference between Rename and Alias?
Rename
is actually changing the name of an object whereas Alias is giving another name
(additional name) to an existing object
19.
What
are various joins used while writing SUBQUERIES?
IN,
NOT IN, IN ANY, IN ALL, EXISTS, NOT EXISTS.
20.
How
you will avoid your query from using indexes?
By
changing the order of the columns that are used in the index, in the Where
condition, or by concatenating the columns with some constant values.
