1. 1. What is SQL?
SQL stands for structure query language It is standard language used to
maintain the relational database perform Many difficult data manipulation
operations on the data. SQL was initially invented in 1970,
It is a database language used for database creation, deletion, fetching
and modifying rows etc. sometimes it is pronounced as ‘sequel’. We can also use
it to handle organized data comprised of entities (variables) and relations
between different entities of the data.
2. When SQL appeared?
SQL first appeared in 1974 It
is one of the most used languages for maintaining the relational database In
1986 SQL became the standard of the American National Standards Institute
(ANSI) and ISO (International Organization for Standardization) in 1987
3. 3. What is clustered Index in SQL?
A clustered index is actually
a table where the data for the rows are stored. It determines the order of the
table database on the key-values that can sort in only one direction. Each
table can have only one clustered index. It is the only index, which has been
automatically created when the primary key is generated. It many data
modifications needed to be done in the table then clustered are preferred
4. 4. What are the usages of SQL?
SQL is responsible for
maintaining the relational data and the data structures present in the database
.some of the common usage are given below
a. To execute queries against a database
b. To retrieve data from a database
c. To insert records in a database
d. To updates records in a database
e. To delete records from a database
f.
To
create new database
g. To create new tables in a database
h. To create new views in database
i.
To
perform complex operation on the database
5. Does SQL support programming
language features?
SQL refers to the standard
query language .Therefore it is true that SQL is a language but does not
actually support the programming language. It is common language that doesn’t
have a loops, conditional statements and logical operations. It cannot be used
for anything other than data manipulation. The primary purpose of the SQL is to
maintain, retrieve, manipulate, update, delete and perform complex operations
like joins on the data present in the database.
6. 6. What is the purpose of DDL Language?
DDL stands for Data definition language .It is the subset of a databases that defines the data structure of the database when the database is created for Example:- we can use the DDL command to add, remove or modify tables It consists of the following commands CREATE, ALTER and DELETE database objects such as schema tables, indexes ,view, sequence, etc
.
7 What are the subsets of the SQL?
The following are the four
significant subsets of the SQL
a. Data definition language (DDL):-
It defines the data structure that consists
of the commands like CREATE, ALTER, DROP, etc
b. Data manipulation language(DML):-
It is used to manipulate existing
data in the database .The commands in this category are SELECT, UPDATE, INSERT,
etc
c. Data control language :-
It controls access to the data stored in
the database .The commands in this category include GRANT and REVOKE
d. Transaction control language(TCL):-
It is used to deal with the
transaction operations in the database. The commands in this category are
COMMIT, ROLLBACK, SET TRANSACTION, SAVEPOINT, etc
8. 8. What is primary key?
A primary key is a field or
the combination of fields that uniquely identifying each record in the table.
It is one the special kind of unique key. If the columns contains a primary key
it cannot be null or empty .A table can have more than one primary key. It
always stores unique values into a row
9. 9. What do you mean by table a field in
SQL?
A table refers to a collection
of data in an organised manner in form of rows and columns . A field refers to
the number of columns in a table.
Example:- Table- StudentInformation
Field-StuId, StuName, StuMarks etc
10. What are constraints?
Constraints in SQL are used
to specify the limit on the data type of the table. I can be specified while
creating an altering the table statements. The sample of the constraints are-
a. NOT NULL
b. CHECK
c. DEFAULT
d. UNIQUE
e. PRIMARY KEY
f. FOREIGN KEY
11. Explain different types of
Normalization?
There are many successive levels of
normalizations. These are called normal forms each consecutive normal form
depends on the previous one. The first three normal forms are usually adequate.
a. First normal form(INF)-
No repeating groups within rows
b. Second normal form(SNF)-
Every non-key (supporting) column value
is dependent on the whole primary key.
c. Third normal form(TNF)-
Dependent solely on the primary key an
no other non-key (supporting) column value.
12 What do you mean by “Trigger “ in SQL?
Trigger in SQL is are a special type
of stored procedures that are defined to execute automatically in place or after data modification . It allows
you to execute a batch of the code where an insert, update or any other query
is executing against a specific table.
13. What is difference between cross join and
natural join?
The cross joins produces the cross product
or Cartesian product of two tables whereas the natural join is based on all the
columns having the same name and data types in both the tables.
14. What is
the need for group function in SQL?
Group function work on the set of rows and
return on the result per group. Some of
the commonly used group functions are – AVG, COUNT, MAX, MIN, SUM, VERIANCE
15. How can
you fetch records from two tables?
You can fetch common records from two
tables using INTERSECT.
16. What
are the different set operators available in SQL?
Some of the available set operators are
UNION, INTERSECT, or MINUS operator.
17. What is
stored procedure?
A stored procedure is a function which
consists of many SQL statements to access he database system Several SQL
statements are consolidated into a stored procedure and execute them whenever
and wherever required which saves time and avoid writing code again and again
18. What is
UNIQUE key?
Uniquely identifies a single row in the
table. Multiple values per table in table .NULL values allowed.
19. What is the difference between CHAR and VARCHAR
data type in SQL?
Both CHAR and VARCHAR are used for characters
data type but VARCHAR is used for character string of variable length whereas
CHAR is used for strings of fixed length.
Example:-
CHAR(10) can only store 10 characters and will not be able to store a string of
any other length whereas VARCHAR(10) can store any length i.e. 6,8,2 in this variable
20. What is
the difference between SQL and MYSQL?
|
SQL |
MYSQL |
|
SQL is Standard language which stands for structured query language
based on the English language |
MYSQL is a database
management system |
|
SQL is the core of
the relational database which is used for accessing and managing database |
MYSQL is an
RDBMS(Relational database management system) such as SQL server, Informix etc. |
21. What is
relationship and what are they?
Relation or links are between entities
that have something to do with each other .Relationships are defined as the
connection between the tables in a database .There are various relationships
namely:
a. One to one relationship
b. One to many relationship
c. Many to one relationships
d. Self referencing relationship
22. Explain different type’s index in SQL?
There are three types of index in SQL namely:-
a. UNIQUE Index-
This index does not allow the field to
have duplicate if the column is unique indexed. It is a primary key is defined
a unique index can be applied automatically
b. Clustered index :-
This index records the physical order
of the table and searches based on the basis of key values .Each table can only
have one clustered index.
c. Non-clustered index:-
Non-clustered index does not alter the
physical order of the table and maintains a logical order of the data. Each table
can have many non-clustered indexes
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