Most Popular SQL Interview Questions For Basic To Advanced

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Most Popular SQL Interview Questions For Basic
To Advanced Analytics Training hub
hese SQL Interview Questions are completely
dedicated to Modernization of the way we used to
maintain records has changed drastically, a lot
of data being generated nowadays are in the form
of pictures or videos that have become our sole
source of keeping memories intact for many years
to come. Similarly, multiple organizations and
firms have employed a similar method in storing
the company data in the form of digitized
documents stored away in Database Management
Systems (DBMS) which require a special style of
language to mine or extract data that the company
wishes to extract from its database and here
where SQL comes in. What is SQL? Structured
Query Language (SQL) is a domain-specific
programming language that is utilized by skilled
professionals to manage data stored in the
companys database. SQL skills are in high demand
in the market and serve as the foundational
basics for any professional looking for a job or
brighter prospects in the data industry. Here
are a set of SQL Interview Questions that we
believe you should prepare for SQL before going
for an interview. Here are Popular SQL Interview
Questions Answers Lists- Q1. Describe a
DBMS? Database Management System (DBMS) is
software that is solely responsible for
creating, controlling, maintaining, and use of a
database. DBMS may be
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defined as a folder that manages data in a
database rather than saving a file in the
system. Q2. Define an RDBMS? RDBMS abbreviates
for Relational Database Management System. It is
categorized with the storage of data into a
compilation of tables, which are linked by
similar topics between the columns of a table. It
aids the user with relational operators to
influence the data stored in the tables. Q3.
Describe SQL? SQL abbreviates to Structured
Queried Language and aids the operator to
communicate with the database. It is a standard
operating language that helps execute
responsibilities such as recovery, updating,
incorporating, and expunging data from the
database. Q4. Define a Database? It is a
structured table of data made to easily access,
store, retrieve, and manage data. Q5. Describe
MySQL? It is a multi-threaded, multiuser
structured query language database management
system with more than 11 million installations
across the globe. The language is the second
most well-known and popularly used open-source
database programming in use. MySQL is an
oracle-sponsored relational database management
system (RDBMS) built on structured query
language. It is supported by several operating
systems which include Windows, LINUX, iOS,
etc. Q6. My SQL has been written in which
language?
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• C C are the languages in which MySQL has been
  written
• Q7. Mention the technical specifications of
  MySQL?
• Below are the technical specifications of MySQL-
• Drivers
• Flexible structure
• Geospatial support
• Graphical tools
• JSON support
• OLTP and transactions
• High performance
• Manageable and easy to use
• MySQL Enterprise Monitor
• MySQL Enterprise Security
• Replication and high availability
• Security storage management
• Q8. Describe the difference between SQL and
  MySQL?
• SQL stands for structured query language and is
  used to interact with databases like MySQL
• MySQL is a database management system used for
  the structured storage of data

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• There are 4 noticeable differences between a
  database a table-
• Tables showcase structured data in a database,
  whereas a database is a collection of tables
• Tables are grouped with relations to create a
  dataset the dataset forms the database.
• Data stored in the table in any form is part of
  the database, but the other way around is not
  possible.
• A table is a collection of rows and columns used
  to store data,
• whereas a database is a collection of organized
  data and features used to access tables.
• Q10. Distinguish between Tables and fields?
• A table is a compilation of cells that are
  structured in a model which eventually form
  tables and rows. Columns may be categorized as a
  vertical collection of cells and rows may be
  categorized as a horizontal collection of cells.
• There is also a reference to the cells laid out
  in a column to create an entity also termed a
  field once a header is provided to the so-called
  column.
• A field may have several rows which may
  constitute a record. E.g.
• Table name- Employee
• Field names- Emp ID, Emp Name, Date of Birth
  Data- 2866, Daniel Decker, 29/02/1984
• Q11. What is the purpose of using a MySQL
  database server?
• Below are some of the reasons why MySQL server is
  so famous with its users-

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• MySQL is an open-source database management
  system that is free of charge for private
  developers and small enterprises.
• MySQLs community is vast and supportive, thus
  any issues faced are resolved at the earliest.
• Has multiple stable versions available
• It extremely quick, dependable and is
  beginner-friendly
• The download is free of cost
• Q12. Describe the various tables present in
  MySQL?
• There are majorly 5 tables present in MySQL
• MyISAM
• Heap
• Merge
• INNO DB
• ISAM
• Q13. How can an Operator install MySQL?
• There are multiple ways of installing MySQL in
  ones system, but the best way to do it is
  manual. The manual installation allows the user
  to gain a better understanding of the system and
  aids in an additional grasp of the database.
  There are several benefits linked to the manual
  installation of MySQL-
• Reinstalling, creating backups, or moving
  databases can be achieved in less than a minute.
• Provides precise control over how and when MySQL
  closes or starts.

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• In WINDOWS MySQL command-line tool shows the
  version information without using any flags, but
  for a piece of more detailed information the
  operator may always feed in the below-mentioned
  command
• MySQLgt SHOW VARIABLES LIKE version.
• and it will show a detailed discretion of the
  version of SQL that the user is using.
• Q15. How to add columns in MySQL?
• Several cells in a table are what may constitute
  a column and a set of cells in a column
  constitutes a row. To add columns in MySQL, the
  following statement of ALTER TABLE may be used
• ALTER TABLE table_name
• ADD COLUMN column_name column_definition FIRSTAF
  TER existing_column.
• Q16. In MySQL how can you delete a table?
• The drop table statement not only removes the
  data in the table, but it also removes the
  structure and definition from the database
  permanently. Thus, the user needs to be
  extremely careful whilst using this command, the
  reason is that once deleted there is no recovery
  option in MySQL. The command is as follows-
• DROP TABLE table_name
• Q17. Define a Primary Key?
• A primary Key may be described as a compilation
  of fields that meticulously define a row. This
  is a Unique Key and has an unspoken NOT NULL
  constraint, implicating Primary keys cannot have
  NULL values.

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• This key provides a separately pre-defined
  constraint that exclusively distinguishes every
  record in the database which insinuates a
  distinctiveness for the column or the set of
  columns.
• Q19. Define a Foreign Key?
• This is a key that can be linked to the Primary
  Key of another table. Connections need to be
  fabricated between the two tables by providing a
  reference to the foreign key with the primary key
  of another table.
• Q20. Describe a Join?
• It is a keyword utilized to question data from
  multiple tables established on the connections
  between the fields of the table. Keys play a
  crucial part when JOINs are employed.
• Q21. Describe the multiple JOIN and explain
  each?
• JOINs are tools that help the user retrieve data
  and depend on the links between tables.
  Following are the types of JOIN used in SQL-
• Inner JOIN This JOIN is used to return rows
  with at least a single match of rows between
  tables
• Right, JOIN This JOIN helps return rows that
  are similar between
• tables and all rows of the right-hand side table.
  To simplify this JOIN returns all rows from the
  right-hand side table irrespective of any
  matches from the left-hand side table.
• Left JOIN This JOIN helps return rows that are
  similar between tables and all rows of the
  left-hand side table. To simplify this JOIN
  returns all rows from the left-hand side table
  irrespective of any matches from the right-hand
  side table.
• Full JOIN This JOIN returns rows if there are
  any similar rows in any of the tables. So
  basically, this JOIN returns all the rows from
  both the right-hand and left-hand side tables.

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• Q22. Define Normalization?
• It is the procedure of reducing redundancies and
  dependencies by structuring fields and tables of
  a database. The primary motive of Normalization
  is to add, modify, and delete that can be merged
  into a single table.
• Q23. Define De-Normalization?
• It is a method employed to gain access to data
  from higher to lower normal types of databases.
  It is also a way of implementing redundancy into
  a table by integrating data from the correlated
  tables.
• Q24. Distinguish the multiple normalizations?
• Normalizations may be dissected into 5 forms-
• First Normal Form (1NF) - It helps in
  eliminating all identical columns from a table
  which aids the formation of tables for the
  associated data and recognition of distinctive
  columns.
• Second Normal Form (2NF) Meeting all the
  obligations of the 1NF. Retaining the subsets of
  data in separate tables and the creation of
  relations between tables using primary keys.
• Third Normal Form (3NF) This shall meet all the
  constraints of 2NF and eradicate the columns
  which are not reliant on the primary key
• limits.
• Fourth Normal Form (4NF) Meeting all the
  obligations of the 3NF and it shall not have
  multi-valued dependencies.
• Q25. Define a View?
• The view is a computer-generated table that
  comprises a subsection of data enclosed in a
  table. Views are NOT virtually present and
  require a lesser amount of storage capacity. The
  view can have data of one or more tables pooled
  in one and depends on the connection.
• Q26. Define an Index?

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• An index is a routine tweaking method to permit
  faster reclamation of records from a table. An
  Index designs an entry for every value which
  makes data recovery quicker.
• Q27. Describe the distinct kinds of Indexes?
• There are primarily 3 types of Indexs-
• Unique Index This style of Indexing does not
  grant the field to have identical values if the
  column is uniquely indexed. This Index can be
  used spontaneously once the primary key is
  defined.
• Clustered Index This style of index rearranges
  the raw order of the table and searches based on
  key values. Each table may consist of only one
  Clustered Index.
• Non-Clustered Index Non-Clustered Index does
  not modify the raw order of the table and
  retains the plausible order of data. Each table
  may consist of 999 non-clustered indexes.
• Q28. Define a Cursor?
• A database cursor is a command which facilitates
  a cross-over of the rows/records in a table.
  This may be visible as a hint to one row in a
  collection of rows. It is extremely useful for
  traversing the retrieval, addition, and removal
  of database archives.
• Q29. Define a Database relationship and what are
  they in SQL?
• It is defined as the link between the tables in a
  database. There are several database-based
  relationships, and they are as follows-
• One to One relationship
• To Many relationships
• Many to One relationship
• Self-referencing relationship

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• Q30. Describe a Query?
• A database query is a code created to recover
  information from the database. The query may be
  fabricated in a way to match the users
  expectation of the result set which may simply
  be a question to the database.
• Q31. Describe a Subquery?
• As the word describes, it is a query inside a
  query. The exterior query is known as the Main
  Query and the innermost query is called a
  Subquery. Subqueries are forever implemented
  first and the outcome from the Subquery is then
  passed on to the main query.
• Q32. Describe the types of Subqueries?
• There are majorly 2 styles of subqueries-
• Correlated Subquery These cannot be considered
  as independent queries but may refer to the
  column in a table listed in the FROM the list of
  the main query.
• Non-Correlated Subquery These may be considered
  as independent queries and the output of these
  subqueries may be substituted in the
• main query.
• Q33. Define a Stored Procedure?
• This procedure is a function that comprises
  several SQL statements to access the DBMS.
  Multiple SQL statements are compiled into a
  Stored Procedure and may be employed anywhere
  as per requirement basis.
• Q34. Define a Trigger?
• The trigger is a code that automatically executes
  with some event on a table or with a view in a
  database. E.g., On the joining of a new hire, new
  records need to be entered in fields like
  employee ID, Name, Date of birth, etc.

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Q35. Distinguish between DELETE and TRUNCATE
commands?

• DELETE command is utilized to delete rows from
  the table and a WHERE clause may be applied for
  a provisional set of considerations. Commit and
  Rollback may be executed post deletion of the
  statement.
• TRUNCATE deletes every row from the table.
  Truncate control cannot be turned backward.
• Q36. Define Local and global variables and
  describe their disparities?
• Local variables are the variables that can be
  applied or occur within the function. They are
  unknown to the other functions and cannot be
  referred to or utilized. Variables can be
  established whenever the functions are called.
• Global variables are the variables that can be
  employed or be present all over the program. An
  identical variable proclaimed in a global
  variable cannot be utilized in functions. Global
  variables cannot be established whenever a
  particular function is called.
• Q37. Define a CONSTRAINT?
• A constraint may be employed to restrict the data
  type of a table. It may also be specified at the
  time of creating or altering the table. Some
  examples of constraints are-
• NOT NULL
• CHECK
• DEFAULT
• UNIQUE
• PRIMARY KEY
• FOREIGN KEY

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Q38. Define Data Integrity? It defines the
precision and consistency of the data stored in a
database. It may also identify integrity
constraints to implement business guidelines on
the data when it is registered into the
application or database. Q39. Describe auto
Increment? This enables the operator to fabricate
a new number to be generated when a record is
inserted into the table. AUTOINCREMENT keyword
may be used in Oracle and IDENTITY keyword may
be used in an SQL SERVER. This keyword is used
when the primary key is used. Q40.Distinguish betw
een Cluster and Non- Cluster Index? Cluster
Index is employed for the convenient recovery of
data from the database by adjusting the way the
records are stored. A database sorts out rows by
columns which are destined to be Clustered
Index. A non-Clustered Index does not adjust the
way data was stored in the database, rather
fabricates a completely different entity inside
the table. It usually points back to the
original table rows after investigating. Q41.
Describe a Datawarehouse? It is a fundamental
storehouse of data from numerous data sources.
Data are collected, transformed, and made
available for mining and online processing.
Warehouse data have a subcategory of data dubbed
as Data Mart. Q42. Define a Self-Join? It is a
query employed to evaluate itself. It is utilized
to assess values in a column with other values
in the same column and table.
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• Q43. Define a Cross-Join?
• Cross join describes as a query to calculate the
  results of the number of rows in the first table
  multiplied by several rows in the second table.
  If a WHERE clause is applied in a cross join,
  then the query will act like an INNER JOIN.
• Q44. Describe User Defined functions and their
  types?
• User-defined functions are fabricated to create
  logic whenever required. It is not required to
  write the same logic multiple times. Rather, the
  function may be called or deployed at any given
  point in time.
• There are 3 styles of User-defined functions-
• Scalar Functions returns unit, return clause
  defined by variant
• Inline table-valued functions, return table as a
  return
• Multi-statement valued functions returns table as
  a return
• Q45. Describe Collation?
• It describes as a compilation of guidelines that
  establish how character data may be categorized
  and compared. It can be used to assess A and
  other language characters, also depending on the
  width of the characters.
• all values may be used to compare these character
  data.
• Q46. Describe the distinct styles of Collation
  sensitivity?
• These are the different types of collation
  sensitivities-
• Case Sensitivity A a, and B b.
• Accent Sensitivity

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• Width Sensitivity Single-byte double-byte
  character.
• Q47. Define recursive Stored Procedure?
• A stored procedure that demands by itself until
  it achieves some kind of boundary condition.
  This recursive function or procedure helps
  computer operators use the identical set of
  codes n number of times.
• Q48. How can a user add foreign keys in MySQL?
• This is the key to linking one or more tables
  together in MySQL. It helps in matching the
  primary key field of another table to connect the
  two tables. It allows the user to have a
  parent-child relationship within the tables. This
  can be executed either way-
• Using the CREATE TABLE command
• Using the ALTER TABLE command
• Following is the syntax used to define a foreign
  key using CREATE or ALTER TABLE
• CONSTRAINT constraint_name
• FOREIGN KEY foreign_key_name (col_name, )
  REFERENCES parent_tbl_name (col_name, )
• Q49. Describe how can the user create a database
  in MySQL workbench?
• To do so the initial step would be to-
• launch the MySQL workbench and log in using a
  username and password
• Choose the Schema menu from the navigation tab

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• Right-click under the schema menu and pick the
  Create Schema option.
• Or
• Click on the database icon ( similar to a barrel)
• A new dialog box would appear
• After filling in all the details in the dialog
  box
• Click on Apply and Finish to complete the
  database creation.
• Q50. How can the user create a Table in MySQL
  workbench?
• Launch the MySQL workbench
• Go to the navigation tab
• Choose the Schema Menu which will showcase all
  the previously created databases
• Select any database and right-click on it
• In the sub-menus, we need to select the tables
  option
• Right-click on the tables sub-menu
• Choose Create table Option

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