hot sql database Job Interview Questions And Answers

What are two methods of retrieving SQL?

• Select 
  
• Cursor
  

sql database   2013-04-30 17:45:23

what is a cursor?

sql database   2013-04-30 17:47:40

What cursor type do you use to retrieve multiple recordsets?

sql database   2013-04-30 17:48:23

What is the difference between a "where" clause and a "having" clause?

sql database   2013-04-30 17:49:10

What is the basic form of a SQL statement to read data out of a table?

sql database   2013-04-30 17:50:06

What structure can you implement for the database to speed up table reads?

sql database   2013-04-30 17:51:00

What are the tradeoffs with having indexes?

sql database   2013-04-30 17:51:37

What is a "join"?

sql database   2013-04-30 17:58:55

What is "normalization"? "Denormalization"? Why do you sometimes want to denormalize?

Normalizing data means eliminating redundant information from a table and organizing the data so that future changes to the table are easier. Denormalization means allowing redundancy in a table. The main benefit of denormalization is improved performance with simplified data retrieval and manipulation. This is done by reduction in the number of joins needed for data processing.

Sql Database interview question

sql database   2013-05-01 18:13:11

What is a primary key?

A PRIMARY INDEX or PRIMARY KEY is something which comes mainly from database theory. From its behavior is almost the same as an UNIQUE INDEX, i.e. there may only be one of each value in this column. If you call such an INDEX PRIMARY instead of UNIQUE, you say something about your table design, which I am not able to explain in few words. Primary Key is a type of a constraint enforcing uniqueness and data integrity for each row of a table. All columns participating in a primary key constraint must possess the NOT NULL property.

Sql Database interview question

sql database   2013-05-01 18:17:16

What is a functional dependency? How does it relate to database table design?

Functional dependency relates to how one object depends upon the other in the database. for example, procedure/function sp2 may be called by procedure sp1. Then we say that sp1 has functional dependency on sp2.

Sql Database interview question

sql database   2013-05-01 18:18:13

Why can a "group by" or "order by" clause be expensive to process?

Processing of "group by" or "order by" clause often requires creation of Temporary tables to process the results of the query. Which depending of the result set can be very expensive.

Sql Database interview question

sql database   2013-05-01 18:20:07

What is "index covering" of a query?

Index covering means that "Data can be found only using indexes, without touching the tables"

Sql Database interview question

sql database   2013-05-01 18:20:57

What types of join algorithms can you have?

• there are 3 kinds of joins in sql server
• nested table,merge and hash joins.all of these depend on the resource available,merge and hash consume a lot of memory.
• nested table should have indexes

sql database   2013-05-01 18:21:58

What is a constraint?

A constraint allows you to apply simple referential integrity checks to a table. There are four primary types of constraints that are currently supported by SQL Server:
PRIMARY/UNIQUE - enforces uniqueness of a particular table column.
DEFAULT - specifies a default value for a column in case an insert operation does not provide one.
FOREIGN KEY - validates that every value in a column exists in a column of another table.
CHECK - checks that every value stored in a column is in some specified list. Each type of constraint performs a specific type of action. Default is not a constraint. NOT NULL is one more constraint which does not allow values in the specific column to be null. And also it the only constraint which is not a table level constraint.

Sql Database interview question

sql database   2013-05-01 18:14:56

What types of index data structures can you have?

An index helps to faster search values in tables. The three most commonly used index-types are: - B-Tree: builds a tree of possible values with a list of row IDs that have the leaf value. Needs a lot of space and is the default index type for most databases. - Bitmap: string of bits for each possible value of the column. Each bit string has one bit for each row. Needs only few space and is very fast.(however, domain of value cannot be large, e.g. SEX(m,f); degree(BS,MS,PHD) - Hash: A hashing algorithm is used to assign a set of characters to represent a text string such as a composite of keys or partial keys, and compresses the underlying data. Takes longer to build and is supported by relatively few databases.

Sql Database interview question

sql database   2013-05-01 18:15:58

What is a trigger?

Triggers are stored procedures created in order to enforce integrity rules in a database. A trigger is executed every time a data-modification operation occurs (i.e., insert, update or delete). Triggers are executed automatically on occurance of one of the data-modification operations. A trigger is a database object directly associated with a particular table. It fires whenever a specific statement/type of statement is issued against that table. The types of statements are insert,update,delete and query statements. Basically, trigger is a set of SQL statements A trigger is a solution to the restrictions of a constraint. For instance:
1.A database column cannot carry PSEUDO columns as criteria where a trigger can.
2. A database constraint cannot refer old and new values for a row where a trigger can.

Sql Database interview question

sql database   2013-05-01 18:19:17

What is a SQL view?

An output of a query can be stored as a view. View acts like small table which meets our criterion. View is a precomplied SQL query which is used to select data from one or more tables. A view is like a table but it doesn’t physically take any space. View is a good way to present data in a particular format if you use that query quite often. View can also be used to restrict users from accessing the tables directly.

Sql Database interview question

sql database   2013-05-01 18:22:45

What is the difference between oracle,sql and sql server ?

Oracle is based on RDBMS.SQL is Structured Query Language.SQL Server is another tool for RDBMS provided by MicroSoft.

Sql Database interview question

sql database   2013-05-01 18:23:37

why you need indexing ? where that is stroed and what you mean by schema object? For what purpose we are using view?

We cant create an Index on Index.. Index is stoed in user_index table.Every object that has been created on Schema is Schema Object like Table,View etc.If we want to share the particular data to various users we have to use the virtual table for the Base table...So tht is a view.indexing is used for faster search or to retrieve data faster from various table. Schema containing set of tables, basically schema means logical separation of the database. View is crated for faster retrieval of data. It's customized virtual table. we can create a single view of multiple tables. Only the drawback is..view needs to be get refreshed for retrieving updated data.

Sql Database interview question

sql database   2013-05-01 18:24:13