cursors / primary key / trigger / view questions

Types of cursors in SQL ?

* Static
* Dynamic
* Forward-only
* Keyset-driven

What is a “primary key”?

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.For example “user Id” should be unique for users, so we can make that field a s primary key in some tables for making sure that value wont repeat.

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 occurrence 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.

What is “index covering” of a query?
Index covering means that “Data can be found only using indexes, without touching the tables”

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.Its mainly used to view the data from various tables.

What is blocking and when it is happening?

Blocking happens when one connection from an application holds a lock and a second connection requires a conflicting lock type. This forces the second connection to wait, blocked on the first.

How do you implement one-to-one, one-to-many and many-to-many relationships while designing tables?

One-to-One relationship can be implemented as a single table and rarely as two tables with primary and foreign key relationships.One-to-Many relationships are implemented by splitting the data into two tables with primary key and foreign key relationships.Many-to-Many relationships are implemented using a junction table with the keys from both the tables forming the composite primary key of the junction table.

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.

What is a “constraint” in SQL?

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.
* 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.

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.

What’s the maximum size of a row in SQL table?

8060 bytes.

What is the difference between a “where” clause and a “having” clause in SQL ?

“Where” Clause in SQL is a kind of restiriction statement. You use where clause to restrict all the data from DB.Where clause is using before result retrieving. But Having clause is using after retrieving the data.Having clause is a kind of filtering command from the selected data.

What’s the difference between a primary key and a unique key?

Both primary key and unique enforce uniqueness of the column on which they are defined. But by default primary key creates a clustered index on the column, where are unique creates a nonclustered index by default. Another major difference is that, primary key doesn’t allow NULLs, but unique key allows one NULL only

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Testing Again

Software Methodologies - Waterfall, SCRUM

Scrum Methodology

Scrum is an agile project management method, which can be used to develop a product or manage any work. It produces a potentially shippable set of product functionality at the end of every iteration or sprint.


Key highlights of Scrum method :


· It is an agile process to manage a project
· A team-based approach to iteratively develop application or product when requirements are rapidly changing
· A way to improve project team communication and maximize co-operation
· A way to improve productivity
· A method that controls the conflicting interests and needs
· A way to identify project impediments proactively and its timely resolution
· It is scalable from single projects to entire organizations