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1. |
What is normalization |
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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. |
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2. |
What is a Stored Procedure |
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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.
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3. |
Can you give an example of Stored Procedure ? |
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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.
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4. |
What is a trigger? |
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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.
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5. |
What is a view? |
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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.
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6. |
What is an Index? |
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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.
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7. |
What is the basic difference between clustered and a
non-clustered index? |
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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.
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8. |
What are cursors? |
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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.
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9. |
Can you tell the difference between DELETE & TRUNCATE
commands? |
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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.
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10. |
Can we use Truncate command on a table which is
referenced by FOREIGN KEY? |
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No. We cannot use Truncate command on a table with
Foreign Key because of referential integrity.
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11. |
What is the difference between a HAVING CLAUSE and a
WHERE CLAUSE? |
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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.
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12. |
What do you mean by COLLATION? |
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Collation is basically the sort order. There are three
types of sort order Dictionary case sensitive, Dictonary
- case insensitive and Binary.
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13. |
What are Joins ? |
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Join actually puts data from two or more tables into a
single result set.
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14. |
Can you explain the types of Joins that we can have with
Sql Server? |
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There are three types of joins: Inner Join, Outer Join,
Cross Join
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15. |
What is difference between UNIQUE and PRIMARY KEY
constraints? |
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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).
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16. |
What is a OUTER JOIN? |
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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.
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17. |
When do you use WHERE clause and when do you use HAVING
clause? |
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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.
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18. |
What is difference between Rename and Alias? |
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Rename is actually changing the name of an object
whereas Alias is giving another name (additional name)
to an existing object
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19. |
What are various joins used while writing SUBQUERIES? |
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IN, NOT IN, IN ANY, IN ALL, EXISTS, NOT EXISTS.
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20. |
How you will avoid your query from using indexes? |
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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. |