The SQL too UNIX are ii of the most essential science for whatever back upwards or evolution job. It doesn't affair whether y'all are applying for Java developer or C++ developer, Python developer or Ruby programmer, SQL too UNIX ever direct around role to play. Hence, it's imperative for whatever programmer to laid upwards both SQL too UNIX good earlier going for whatever project interview. This becomes fifty-fifty to a greater extent than of import if y'all are going for a back upwards engineer role. Since the primary project of back upwards professional person is to aspect after production environment, which often runs on Linux, it's must for them to direct a expert cognition of both Linux operating organisation too ascendance line. They should know what they are doing because an wrong grep or rm ascendance tin direct downward the whole production system. That's why they are extensively questioned too tested inwards their UNIX skill.
Same is truthful for SQL because most of the existent globe organisation uses a relational database for backend e.g. Oracle, MySQL or Microsoft SQL Server too back upwards professional person often demand to run queries, study stored physical care for or write procedures to generate reports.
Just similar UNIX command, a careless SQL query likewise has potential to direct your production organisation to halt too y'all should ever create diligent earlier running whatever query against alive environs e.g. running them inwards UAT or QA environs earlier running them inwards Production, y'all tin discover to a greater extent than such SQL tips here.
Because of these reasons, SQL too UNIX croak essential skills for whatever software back upwards professional. I direct interviewed a lot of back upwards guys, particular for Java applications too I direct ever focused on their center Java, too back upwards skills along amongst SQL too UNIX.
This listing contains around of the questions which I intend rattling of import from a Java back upwards perspective, too many of them are genuinely asked inwards existent interviews. If y'all are going for whatever Java back upwards role, y'all tin hold off around SQL too Linux questions along amongst Java JEE question. I encourage y'all to croak through this listing to acquire an thought of what to hold off inwards existent Java back upwards interview.
Btw, this is the instant component division of my listing of interview questions for Java information technology back upwards professional. In the first part, I direct shared xxx essential Java too JEE questions too inwards this part, I'll portion 17 SQL too UNIX questions from diverse Java Support Interviews.
1) What volition occur when a TCP/IP customer stops consuming messages from Server but it's connected? Assume Server is continuously sending messages. (answer)
The message volition locomote stored on sending buffer at the sender terminate because it volition halt receiving the ack from the receiver. If server maintain continues to force messages, the sending buffer volition overflow, throw an mistake to halt the server.
2) What guarantees are provided past times TCP/IP? (answer)
The TCP/IP provides the guaranteed delivery but apart that it likewise provides ordering guarantee i.e. message volition locomote delivered to the customer inwards the same social club they are sent from the sender. This is 1 of the of import argue to consider TCP/IP for ordered messages e.g. orders too trades inwards the fiscal world. See here to discover around expert mass to larn to a greater extent than most TCP/IP protocol from application developer's perspective.
3) How create y'all discover the PID of a physical care for listening on port 8080? (answer)
If the physical care for is running on Linux operating organisation thence it's pretty easy, but job the netstat ascendance to discover the PID of the process, netstat -p shows the PID. Once y'all got the physical care for id, y'all tin job the ps ascendance to discover the physical care for itself. See the respond for a alive example.
4) What is multicasting? (answer)
The multicasting is a networking concept which allows y'all to ship the same messages to multiple clients without sending it to all i.e. without broadcasting it. In the instance of multicasting, at that spot exists a multicast group, which is represented past times a special multicasting IP address. Any customer who wants to have the message sent to this IP address tin bring together this grouping too thence the router volition ensure that novel messages volition locomote delivered to all subscribers.
5) What is the deviation betwixt multicasting too broadcasting? (answer)
Even though both are networking concepts to deliver messages to multiple clients, at that spot is subtle deviation exists betwixt them. In the instance of multicasting, messages are delivered to solely machines which are component division of the multicast grouping patch inwards the instance of broadcasting message is delivered to all machines inwards the network.
6) What is a multicast group? (answer)
H5N1 multicast grouping is a unmarried machine or grouping of machines amongst special multicast IP address i.e. the IP address inwards the arrive at of 224.0.0.0 to 239. 255.255.255. The multicast grouping tin solely locomote used every bit the finish of a datagram, non every bit source.
7) You received an alarm that file organisation is most to fill upwards up, how create y'all discover large files to remove? (answer)
This is 1 of the mutual province of affairs Java programmer face. In Linux, y'all tin job the discover ascendance to search all large files. The discover -size options listing the file amongst their sizes. See my article 10 illustration of discover ascendance inwards UNIX for a consummate example.
8) How create y'all discover the heap dump files inwards Linux? (answer)
The heap dump files are by too large inwards the shape of java_pid.hprof, thence y'all tin easily search them using discover ascendance inwards Linux every bit shown below:
9) How create y'all discover the files currently used past times your Java process? (answer)
You tin job the lsof command to discover all the files, including sockets past times your Java physical care for inwards Linux. The lsof command stands for listing opened upwards files too since everything inwards UNIX is file it tin listing both normal files every bit good every bit opened upwards socket connecter past times whatever process.
volition listing all files opened past times coffee command, and,
volition listing all files opened past times physical care for id 22342.
For a more in-depth discussion on using lsof command and its diverse open, delight read 10 examples of lsof ascendance inwards Linux.
10) How create y'all discover the ports currently used past times a Java process? (answer)
You tin job the netstat or lsof ascendance to discover all the ports currently used past times a Java process, but for that, y'all demand the physical care for id of your Java process. You tin discover the PID using ps too grep ascendance every bit shown below:
$ ps -ef | grep coffee | grep myprocess
Once y'all discover the PID of your Java process, y'all tin job the netstat command to discover the ports currently used this Java physical care for every bit shown inwards the next example:
$ netstat -nap | grep PID
If netstat is non available on your Linux machine y'all tin likewise job the lsof ascendance to discover all the ports used past times a Java physical care for every bit shown below:
$ lsof -i
If y'all desire to larn to a greater extent than most Linux commands I propose y'all to offset complete Linux Command Line Interface (CLI) Fundamentals course of teaching from Pluralsight.
11) Can y'all cite 10 Linux commands y'all job daily? (answer)
This is easy, right? y'all tin cite whatever Linux commands y'all job but brand certain y'all hand a diverseness of commands e.g. commands to search, networking commands, physical care for administration commands, CPU too retention profiling commands etc. Anyway, hither is my listing of 10 Linux commands
ls
top
ps
find
grep
netstat
df
lsof
kill
sort
chmod
If y'all desire to larn to a greater extent than most UNIX commands thence please see The Linux Command Line: H5N1 Complete Introduction, a consummate guide to Linux commands.
12) How create y'all discover the instant highest salary inwards employee table? (answer)
There are many ways to discover the instant highest salary inwards the employee tabular array e.g. y'all tin either job the co-related subquery, or y'all tin job a ranking component division like row_number() and rank(). The inquiry tin locomote fifty-fifty to a greater extent than tricky past times adding duplicates e.g. ii employees amongst the same salary. In that case, y'all tin direct betwixt ranking component division to satisfy the requirement. I direct already written a detailed spider web log postal service most this topic, delight see here for a pair of illustration of finding instant highest salary inwards the employee table.
13) How create y'all discover the duplicate rows inwards a table? (answer)
Again, similar the previous question, at that spot are several ways to discover the duplicate rows inwards tabular array e.g. y'all tin job a ranking component division similar row_number which assign row break depending upon the value y'all inquire too for same values similar inwards the instance of duplicate rows, the row break volition locomote same. You tin likewise the grouping past times clause to discover duplicates e.g.
This 1 of the classic means to discover the duplicate rows inwards a tabular array too it volition piece of work inwards almost all database e.g. Oracle, SQL Server, or MySQL. See here for a detailed respond to this problem.
14) How create y'all take away the duplicate rows from the table? (answer)
This is the follow-up previous inquiry too much tougher than the previous one, peculiarly if y'all are non familiar amongst the ranking functions similar row_number. If y'all solely know most GROUP BY clause thence y'all volition combat to take away duplicate rows because if y'all take away past times emp_id both rows volition locomote removed. Here y'all must job the row_number() function, the duplicate rows volition have row break > 1 e.g.
This volition impress something similar below
John 1
Heroku 1
David 1
David 2
Here instant David is duplicate too y'all tin easily take away it past times giving status where row_number> 1. See here for consummate SQL query too to larn to a greater extent than most solving this job inwards the existent world.
15) What is the deviation betwixt clustered too non-clustered index? (answer)
This is 1 of the often asked database questions, the primary deviation betwixt ii is that at that spot tin locomote solely 1 clustered index on a tabular array patch y'all tin direct to a greater extent than than 1 non-clustered index. The clustered index likewise defines how the information is physically stored on the disk. See here to larn to a greater extent than deviation betwixt these the clustered too non-clustered index inwards the database.
16) How create y'all discover all records modified betwixt ii dates inwards SQL? (answer)
This is 1 of the tricky SQL questions. It looks uncomplicated but when y'all croak too write the SQL query, y'all volition discover that it's non working every bit expected. For example, many programmers volition job the "between" SQL clause to discover all the rows modified betwixt ii dates e.g.
This volition piece of work good inwards most cases but if at that spot is an social club where order_date is midnight of 1st Oct thence it volition likewise locomote picked. You tin locomote to a greater extent than precise past times using the logical operator every bit shown below:
See Querying Microsoft SQL Server to larn to a greater extent than most the appointment too fourth dimension information types too comparison them inwards SQL Server.
17) What is the deviation between count(field) and count(*) in SQL? (answer)
The solely deviation between count(field) and count(*) is that old doesn't count zilch values patch later on does. For example, if y'all direct an emp_name column on your tabular array too it contains 10 valid values too three zilch values then count(emp_name) will render 10 patch count(*) volition render xiii rows.
That's all most SQL too UNIX questions for software back upwards engineers. As I said, these ii technologies are rattling very of import for whatever project too a expert ascendance on these ii goes a long means to secure the job. They are likewise classic technologies i.e. they don't obsolete inwards every pair of twelvemonth too they volition stay pop for several years to come.
Further Learning
Cracking The Coding Interview
Programming Interviews Exposed: Secrets to Landing Your Next Job
Introduction to SQL past times Jon Flanders
Linux Command Line Interface (CLI) Fundamentals
Other Interview questions for software back upwards engineers
Along amongst these questions, y'all should likewise banking firm gibe next interview questions shared earlier to create good on your back upwards project interviews.
Thanks for reading this article thence far. If y'all similar this tutorial thence delight portion amongst your friends too colleagues. If y'all direct whatever question, uncertainty or seeking an respond for something, delight driblet a comment too I'll travail to discover an respond for you.
Same is truthful for SQL because most of the existent globe organisation uses a relational database for backend e.g. Oracle, MySQL or Microsoft SQL Server too back upwards professional person often demand to run queries, study stored physical care for or write procedures to generate reports.
Just similar UNIX command, a careless SQL query likewise has potential to direct your production organisation to halt too y'all should ever create diligent earlier running whatever query against alive environs e.g. running them inwards UAT or QA environs earlier running them inwards Production, y'all tin discover to a greater extent than such SQL tips here.
Because of these reasons, SQL too UNIX croak essential skills for whatever software back upwards professional. I direct interviewed a lot of back upwards guys, particular for Java applications too I direct ever focused on their center Java, too back upwards skills along amongst SQL too UNIX.
SQL too UNIX Questions from Support Engineers
This listing contains around of the questions which I intend rattling of import from a Java back upwards perspective, too many of them are genuinely asked inwards existent interviews. If y'all are going for whatever Java back upwards role, y'all tin hold off around SQL too Linux questions along amongst Java JEE question. I encourage y'all to croak through this listing to acquire an thought of what to hold off inwards existent Java back upwards interview.Btw, this is the instant component division of my listing of interview questions for Java information technology back upwards professional. In the first part, I direct shared xxx essential Java too JEE questions too inwards this part, I'll portion 17 SQL too UNIX questions from diverse Java Support Interviews.
1) What volition occur when a TCP/IP customer stops consuming messages from Server but it's connected? Assume Server is continuously sending messages. (answer)
The message volition locomote stored on sending buffer at the sender terminate because it volition halt receiving the ack from the receiver. If server maintain continues to force messages, the sending buffer volition overflow, throw an mistake to halt the server.
2) What guarantees are provided past times TCP/IP? (answer)
The TCP/IP provides the guaranteed delivery but apart that it likewise provides ordering guarantee i.e. message volition locomote delivered to the customer inwards the same social club they are sent from the sender. This is 1 of the of import argue to consider TCP/IP for ordered messages e.g. orders too trades inwards the fiscal world. See here to discover around expert mass to larn to a greater extent than most TCP/IP protocol from application developer's perspective.
3) How create y'all discover the PID of a physical care for listening on port 8080? (answer)
If the physical care for is running on Linux operating organisation thence it's pretty easy, but job the netstat ascendance to discover the PID of the process, netstat -p shows the PID. Once y'all got the physical care for id, y'all tin job the ps ascendance to discover the physical care for itself. See the respond for a alive example.
4) What is multicasting? (answer)
The multicasting is a networking concept which allows y'all to ship the same messages to multiple clients without sending it to all i.e. without broadcasting it. In the instance of multicasting, at that spot exists a multicast group, which is represented past times a special multicasting IP address. Any customer who wants to have the message sent to this IP address tin bring together this grouping too thence the router volition ensure that novel messages volition locomote delivered to all subscribers.
5) What is the deviation betwixt multicasting too broadcasting? (answer)
Even though both are networking concepts to deliver messages to multiple clients, at that spot is subtle deviation exists betwixt them. In the instance of multicasting, messages are delivered to solely machines which are component division of the multicast grouping patch inwards the instance of broadcasting message is delivered to all machines inwards the network.
6) What is a multicast group? (answer)
H5N1 multicast grouping is a unmarried machine or grouping of machines amongst special multicast IP address i.e. the IP address inwards the arrive at of 224.0.0.0 to 239. 255.255.255. The multicast grouping tin solely locomote used every bit the finish of a datagram, non every bit source.
7) You received an alarm that file organisation is most to fill upwards up, how create y'all discover large files to remove? (answer)
This is 1 of the mutual province of affairs Java programmer face. In Linux, y'all tin job the discover ascendance to search all large files. The discover -size options listing the file amongst their sizes. See my article 10 illustration of discover ascendance inwards UNIX for a consummate example.
8) How create y'all discover the heap dump files inwards Linux? (answer)
The heap dump files are by too large inwards the shape of java_pid.hprof, thence y'all tin easily search them using discover ascendance inwards Linux every bit shown below:
$ discover . -name *.hprof -print
9) How create y'all discover the files currently used past times your Java process? (answer)
You tin job the lsof command to discover all the files, including sockets past times your Java physical care for inwards Linux. The lsof command stands for listing opened upwards files too since everything inwards UNIX is file it tin listing both normal files every bit good every bit opened upwards socket connecter past times whatever process.
$ lsof -c java
volition listing all files opened past times coffee command, and,
$ lsof -p 22342
volition listing all files opened past times physical care for id 22342.
For a more in-depth discussion on using lsof command and its diverse open, delight read 10 examples of lsof ascendance inwards Linux.
10) How create y'all discover the ports currently used past times a Java process? (answer)
You tin job the netstat or lsof ascendance to discover all the ports currently used past times a Java process, but for that, y'all demand the physical care for id of your Java process. You tin discover the PID using ps too grep ascendance every bit shown below:
$ ps -ef | grep coffee | grep myprocess
Once y'all discover the PID of your Java process, y'all tin job the netstat command to discover the ports currently used this Java physical care for every bit shown inwards the next example:
$ netstat -nap | grep PID
If netstat is non available on your Linux machine y'all tin likewise job the lsof ascendance to discover all the ports used past times a Java physical care for every bit shown below:
$ lsof -i
If y'all desire to larn to a greater extent than most Linux commands I propose y'all to offset complete Linux Command Line Interface (CLI) Fundamentals course of teaching from Pluralsight.
11) Can y'all cite 10 Linux commands y'all job daily? (answer)
This is easy, right? y'all tin cite whatever Linux commands y'all job but brand certain y'all hand a diverseness of commands e.g. commands to search, networking commands, physical care for administration commands, CPU too retention profiling commands etc. Anyway, hither is my listing of 10 Linux commands
ls
top
ps
find
grep
netstat
df
lsof
kill
sort
chmod
If y'all desire to larn to a greater extent than most UNIX commands thence please see The Linux Command Line: H5N1 Complete Introduction, a consummate guide to Linux commands.
12) How create y'all discover the instant highest salary inwards employee table? (answer)
There are many ways to discover the instant highest salary inwards the employee tabular array e.g. y'all tin either job the co-related subquery, or y'all tin job a ranking component division like row_number() and rank(). The inquiry tin locomote fifty-fifty to a greater extent than tricky past times adding duplicates e.g. ii employees amongst the same salary. In that case, y'all tin direct betwixt ranking component division to satisfy the requirement. I direct already written a detailed spider web log postal service most this topic, delight see here for a pair of illustration of finding instant highest salary inwards the employee table.
13) How create y'all discover the duplicate rows inwards a table? (answer)
Again, similar the previous question, at that spot are several ways to discover the duplicate rows inwards tabular array e.g. y'all tin job a ranking component division similar row_number which assign row break depending upon the value y'all inquire too for same values similar inwards the instance of duplicate rows, the row break volition locomote same. You tin likewise the grouping past times clause to discover duplicates e.g.
select emp_name, count(*) from employee group by emp_name having count(*) > 1
This 1 of the classic means to discover the duplicate rows inwards a tabular array too it volition piece of work inwards almost all database e.g. Oracle, SQL Server, or MySQL. See here for a detailed respond to this problem.
14) How create y'all take away the duplicate rows from the table? (answer)
This is the follow-up previous inquiry too much tougher than the previous one, peculiarly if y'all are non familiar amongst the ranking functions similar row_number. If y'all solely know most GROUP BY clause thence y'all volition combat to take away duplicate rows because if y'all take away past times emp_id both rows volition locomote removed. Here y'all must job the row_number() function, the duplicate rows volition have row break > 1 e.g.
select emp_name, row_number() over (order by emp_name desc) row_number from Employee
This volition impress something similar below
John 1
Heroku 1
David 1
David 2
Here instant David is duplicate too y'all tin easily take away it past times giving status where row_number> 1. See here for consummate SQL query too to larn to a greater extent than most solving this job inwards the existent world.
15) What is the deviation betwixt clustered too non-clustered index? (answer)
This is 1 of the often asked database questions, the primary deviation betwixt ii is that at that spot tin locomote solely 1 clustered index on a tabular array patch y'all tin direct to a greater extent than than 1 non-clustered index. The clustered index likewise defines how the information is physically stored on the disk. See here to larn to a greater extent than deviation betwixt these the clustered too non-clustered index inwards the database.
16) How create y'all discover all records modified betwixt ii dates inwards SQL? (answer)
This is 1 of the tricky SQL questions. It looks uncomplicated but when y'all croak too write the SQL query, y'all volition discover that it's non working every bit expected. For example, many programmers volition job the "between" SQL clause to discover all the rows modified betwixt ii dates e.g.
select * from Orders where order_date between '20160901' and '20160930'
This volition piece of work good inwards most cases but if at that spot is an social club where order_date is midnight of 1st Oct thence it volition likewise locomote picked. You tin locomote to a greater extent than precise past times using the logical operator every bit shown below:
select * from Orders where order_date >='20160901' and order_date < '20160930'
See Querying Microsoft SQL Server to larn to a greater extent than most the appointment too fourth dimension information types too comparison them inwards SQL Server.
17) What is the deviation between count(field) and count(*) in SQL? (answer)
The solely deviation between count(field) and count(*) is that old doesn't count zilch values patch later on does. For example, if y'all direct an emp_name column on your tabular array too it contains 10 valid values too three zilch values then count(emp_name) will render 10 patch count(*) volition render xiii rows.
That's all most SQL too UNIX questions for software back upwards engineers. As I said, these ii technologies are rattling very of import for whatever project too a expert ascendance on these ii goes a long means to secure the job. They are likewise classic technologies i.e. they don't obsolete inwards every pair of twelvemonth too they volition stay pop for several years to come.
Further Learning
Cracking The Coding Interview
Programming Interviews Exposed: Secrets to Landing Your Next Job
Introduction to SQL past times Jon Flanders
Linux Command Line Interface (CLI) Fundamentals
Other Interview questions for software back upwards engineers
Along amongst these questions, y'all should likewise banking firm gibe next interview questions shared earlier to create good on your back upwards project interviews.
- Frequently asked SQL queries from Interviews - component division 2 (see)
- Frequently asked Java Interview Questions (see)
- Top 50 Multithreading Interview Questions (see)
- Top xxx Array based Interview Questions (see)
- Top xx LinkedList based Interview Questions (see)
- Top 50 Java Programs from Coding Interviews (see)
- 10 Books to Prepare for Coding Interviews (see)
- Difference betwixt Primary too Unique substitution inwards SQL (answer)
- Top 50 Programming questions for telephonic interview (answer)
Thanks for reading this article thence far. If y'all similar this tutorial thence delight portion amongst your friends too colleagues. If y'all direct whatever question, uncertainty or seeking an respond for something, delight driblet a comment too I'll travail to discover an respond for you.
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