What is a CO-RELATED SUBQUERY?
A CO-RELATED SUBQUERY is one that has a correlation name as table or view designator in the FROM clause of the outer query and the same correlation name as a qualifier of a search condition in the WHERE clause of the subquery.2. eg3. SELECT field1 from table1 X4. WHERE field2>(select avg(field2) from table1 Y5. wherefield1=X.field1);(The subquery in a correlated subquery is revaluated for every row of the table or view named in the outer query.)
What are various joins used while writing SUBQUERIES?
Self join-Its a join foreign key of a table references the same table.Outer Join–Its a join condition used where One can query all the rows of one of the tables in the join condition even though they don’t satisfy the join condition.Equi-join–Its a join condition that retrieves rows from one or more tables in which one or more columns in one table are equal to one or more columns in the second table.
What are various constraints used in SQL?
NULLNOT NULLCHECKDEFAULT
What are different Oracle database objects?
TABLESVIEWSINDEXESSYNONYMSSEQUENCESTABLESPACES etc
What is difference between Rename and Alias?
Rename is a permanent name given to a table or column whereas Alias is a temporary name given to a table or column which do not exist once the SQL statement is executed.
What is a view?
A view is stored procedure based on one or more tables, its a virtual table.
What are various privileges that a user can grant to another user?
SELECTCONNECTRESOURCE
What is difference between UNIQUE and PRIMARY KEY constraints?
A table can have only one PRIMARY KEY whereas there can be any number of UNIQUE keys. The columns that compose PK are automatically define NOT NULL, whereas a column that compose a UNIQUE is not automatically defined to be mandatory must also specify the column is NOT NULL.
Can a primary key contain more than one columns?
Yes
How you will avoid duplicating records in a query?
By using DISTINCT
What is difference between SQL and SQL*PLUS?
SQL*PLUS is a command line tool where as SQL and PL/SQL language interface and reporting tool. Its a command line tool that allows user to type SQL commands to be executed directly against an Oracle database. SQL is a language used to query the relational database(DML,DCL,DDL). SQL*PLUS commands are used to format query result, Set options, Edit SQL commands and PL/SQL.
Which datatype is used for storing graphics and images?
LONG RAW data type is used for storing BLOB’s (binary large objects).
How will you delete duplicating rows from a base table?
DELETE FROM table_name A WHERE rowid>(SELECT min(rowid) from table_name B where B.table_no=A.table_no);CREATE TABLE new_table AS SELECT DISTINCT * FROM old_table;DROP old_table RENAME new_table TO old_table DELETE FROM table_name A WHERE rowid NOT IN (SELECT MAX(ROWID) FROM table_name GROUP BY column_name)
What is difference between SUBSTR and INSTR?
SUBSTR returns a specified portion of a string eg SUBSTR(’BCDEF’,4) output BCDE INSTR provides character position in which a pattern is found in a string. eg INSTR(’ABC-DC-F’,'-’,2) output 7 (2nd occurence of ‘-’ )
What is an UTL_FILE.What are different procedures and functions associated with it?
UTL_FILE is a package that adds the ability to read and write to operating system files Procedures associated with it are FCLOSE, FCLOSE_ALL and 5 procedures to output data to a file PUT, PUT_LINE, NEW_LINE, PUTF, FFLUSH.PUT, FFLUSH.PUT_LINE,FFLUSH.NEW_LINE. Functions associated with it are FOPEN, ISOPEN.
Can you use a commit statement within a database trigger?
No
What is the maximum buffer size that can be specified using the DBMS_OUTPUT. ENABLE function?
1,000,000
PHP interview questions and answer
What does a special set of tags do in PHP?
The output is displayed directly to the browser.
What’s the difference between include and require?
It’s how they handle failures. If the file is not found by require(), it will cause a fatal error and halt the execution of the script. If the file is not found by include(), a warning will be issued, but execution will continue.
I am trying to assign a variable the value of 0123, but it keeps coming up with a different number, what’s the problem?
PHP Interpreter treats numbers beginning with 0 as octal. Look at the similar PHP interview questions for more numeric problems.
Would I use print "$a dollars" or "{$a} dollars" to print out the amount of dollars in this example?
In this example it wouldn’t matter, since the variable is all by itself, but if you were to print something like "{$a},000,000 mln dollars", then you definitely need to use the braces.
How do you define a constant?
Via define() directive, like define ("MYCONSTANT", 100);
How do you pass a variable by value?
Just like in C++, put an ampersand in front of it, like $a = &$b
Will comparison of string "10" and integer 11 work in PHP?
Yes, internally PHP will cast everything to the integer type, so numbers 10 and 11 will be compared.
When are you supposed to use endif to end the conditional statement?
When the original if was followed by : and then the code block without braces.
Explain the ternary conditional operator in PHP?
Expression preceding the ? is evaluated, if it’s true, then the expression preceding the : is executed, otherwise, the expression following : is executed.
How do I find out the number of parameters passed into function?
func_num_args() function returns the number of parameters passed in.
If the variable $a is equal to 5 and variable $b is equal to character a, what’s the value of $$b
100, it’s a reference to existing variable.
What’s the difference between accessing a class method via -> and via ::?
:: is allowed to access methods that can perform static operations, i.e. those, which do not require object initialization.
Are objects passed by value or by reference?
Everything is passed by value.
How do you call a constructor for a parent class?
parent::constructor($value)
What’s the special meaning of __sleep and __wakeup?
__sleep returns the array of all the variables than need to be saved, while __wakeup retrieves them.
Why doesn’t the following code print the newline properly?
Because inside the single quotes the \n character is not interpreted as newline, just as a sequence of two characters - \ and n.
Would you initialize your strings with single quotes or double quotes?
Since the data inside the single-quoted string is not parsed for variable substitution, it’s always a better idea speed-wise to initialize a string with single quotes, unless you specifically need variable substitution.
How come the code works, but doesn’t for two-dimensional array of mine?
Any time you have an array with more than one dimension, complex parsing syntax is required. print "Contents: {$arr[1][2]}" would’ve worked.
What is the difference between characters \023 and \x23?
The first one is octal 23, the second is hex 23.
With a heredoc syntax, do I get variable substitution inside the heredoc contents?
Yes.
I want to combine two variables together:
$var1 = 'Welcome to ';
$var2 = softwaaree.blogspot.com';
What will work faster?
Code sample 1:
$var 3 = $var1.$var2;
Or
code sample 2:
$var3 = "$var1$var2";
Both examples would provide the same result - $var3 equal to "Welcome to softwaaree.blogspot.com". However, Code Sample 1 will work significantly faster. Try it out with large sets of data (or via concatenating small sets a million times or so), and you will see that concatenation works significantly faster than variable substitution.
For printing out strings, there are echo, print and printf. Explain the differences?
echo is the most primitive of them, and just outputs the contents following the construct to the screen. print is also a construct (so parentheses are optional when calling it), but it returns TRUE on successful output and FALSE if it was unable to print out the string. However, you can pass multiple parameters to echo, like:
and it will output the string "Welcome to softwaaree.blogspot.com!" print does not take multiple parameters. It is also generally argued that echo is faster, but usually the speed advantage is negligible, and might not be there for future versions of PHP. printf is a function, not a construct, and allows such advantages as formatted output, but it’s the slowest way to print out data out of echo, print and printf.
I am writing an application in PHP that outputs a printable version of driving directions. It contains some long sentences, and I am a neat freak, and would like to make sure that no line exceeds 50 characters. How do I accomplish that with PHP?
On large strings that need to be formatted according to some length specifications, use wordwrap() or chunk_split().
What’s the output of the ucwords function in this example?
$formatted = ucwords("FOR SOFTWARE PROFESSIONAL IS COLLECTION OF INTERVIEW QUESTIONS");
print $formatted;What will be printed is FOR SOFTWARE PROFESSIONAL IS COLLECTION OF INTERVIEW QUESTIONS.
ucwords() makes every first letter of every word capital, but it does not lower-case anything else. To avoid this, and get a properly formatted string, it’s worth using strtolower() first.
What’s the difference between htmlentities() and htmlspecialchars?
htmlspecialchars only takes care of <, >, single quote ‘, double quote " and ampersand. htmlentities translates all occurrences of character sequences that have different meaning in HTML.
What’s the difference between md5(), crc32() and sha1() crypto on PHP?
The major difference is the length of the hash generated. CRC32 is, evidently, 32 bits, while sha1() returns a 128 bit value, and md5() returns a 160 bit value. This is important when avoiding collisions.
So if md5() generates the most secure hash, why would you ever use the less secure crc32() and sha1
Crypto usage in PHP is simple, but that doesn’t mean it’s free. First off, depending on the data that you’re encrypting, you might have reasons to store a 32-bit value in the database instead of the 160-bit value to save on space. Second, the more secure the crypto is, the longer is the computation time to deliver the hash value. A high volume site might be significantly slowed down, if frequent md5() generation is required.
How do you match the character ^ at the beginning of the string?
^\^
The output is displayed directly to the browser.
What’s the difference between include and require?
It’s how they handle failures. If the file is not found by require(), it will cause a fatal error and halt the execution of the script. If the file is not found by include(), a warning will be issued, but execution will continue.
I am trying to assign a variable the value of 0123, but it keeps coming up with a different number, what’s the problem?
PHP Interpreter treats numbers beginning with 0 as octal. Look at the similar PHP interview questions for more numeric problems.
Would I use print "$a dollars" or "{$a} dollars" to print out the amount of dollars in this example?
In this example it wouldn’t matter, since the variable is all by itself, but if you were to print something like "{$a},000,000 mln dollars", then you definitely need to use the braces.
How do you define a constant?
Via define() directive, like define ("MYCONSTANT", 100);
How do you pass a variable by value?
Just like in C++, put an ampersand in front of it, like $a = &$b
Will comparison of string "10" and integer 11 work in PHP?
Yes, internally PHP will cast everything to the integer type, so numbers 10 and 11 will be compared.
When are you supposed to use endif to end the conditional statement?
When the original if was followed by : and then the code block without braces.
Explain the ternary conditional operator in PHP?
Expression preceding the ? is evaluated, if it’s true, then the expression preceding the : is executed, otherwise, the expression following : is executed.
How do I find out the number of parameters passed into function?
func_num_args() function returns the number of parameters passed in.
If the variable $a is equal to 5 and variable $b is equal to character a, what’s the value of $$b
100, it’s a reference to existing variable.
What’s the difference between accessing a class method via -> and via ::?
:: is allowed to access methods that can perform static operations, i.e. those, which do not require object initialization.
Are objects passed by value or by reference?
Everything is passed by value.
How do you call a constructor for a parent class?
parent::constructor($value)
What’s the special meaning of __sleep and __wakeup?
__sleep returns the array of all the variables than need to be saved, while __wakeup retrieves them.
Why doesn’t the following code print the newline properly?
Because inside the single quotes the \n character is not interpreted as newline, just as a sequence of two characters - \ and n.
Would you initialize your strings with single quotes or double quotes?
Since the data inside the single-quoted string is not parsed for variable substitution, it’s always a better idea speed-wise to initialize a string with single quotes, unless you specifically need variable substitution.
How come the code works, but doesn’t for two-dimensional array of mine?
Any time you have an array with more than one dimension, complex parsing syntax is required. print "Contents: {$arr[1][2]}" would’ve worked.
What is the difference between characters \023 and \x23?
The first one is octal 23, the second is hex 23.
With a heredoc syntax, do I get variable substitution inside the heredoc contents?
Yes.
I want to combine two variables together:
$var1 = 'Welcome to ';
$var2 = softwaaree.blogspot.com';
What will work faster?
Code sample 1:
$var 3 = $var1.$var2;
Or
code sample 2:
$var3 = "$var1$var2";
Both examples would provide the same result - $var3 equal to "Welcome to softwaaree.blogspot.com". However, Code Sample 1 will work significantly faster. Try it out with large sets of data (or via concatenating small sets a million times or so), and you will see that concatenation works significantly faster than variable substitution.
For printing out strings, there are echo, print and printf. Explain the differences?
echo is the most primitive of them, and just outputs the contents following the construct to the screen. print is also a construct (so parentheses are optional when calling it), but it returns TRUE on successful output and FALSE if it was unable to print out the string. However, you can pass multiple parameters to echo, like:
and it will output the string "Welcome to softwaaree.blogspot.com!" print does not take multiple parameters. It is also generally argued that echo is faster, but usually the speed advantage is negligible, and might not be there for future versions of PHP. printf is a function, not a construct, and allows such advantages as formatted output, but it’s the slowest way to print out data out of echo, print and printf.
I am writing an application in PHP that outputs a printable version of driving directions. It contains some long sentences, and I am a neat freak, and would like to make sure that no line exceeds 50 characters. How do I accomplish that with PHP?
On large strings that need to be formatted according to some length specifications, use wordwrap() or chunk_split().
What’s the output of the ucwords function in this example?
$formatted = ucwords("FOR SOFTWARE PROFESSIONAL IS COLLECTION OF INTERVIEW QUESTIONS");
print $formatted;What will be printed is FOR SOFTWARE PROFESSIONAL IS COLLECTION OF INTERVIEW QUESTIONS.
ucwords() makes every first letter of every word capital, but it does not lower-case anything else. To avoid this, and get a properly formatted string, it’s worth using strtolower() first.
What’s the difference between htmlentities() and htmlspecialchars?
htmlspecialchars only takes care of <, >, single quote ‘, double quote " and ampersand. htmlentities translates all occurrences of character sequences that have different meaning in HTML.
What’s the difference between md5(), crc32() and sha1() crypto on PHP?
The major difference is the length of the hash generated. CRC32 is, evidently, 32 bits, while sha1() returns a 128 bit value, and md5() returns a 160 bit value. This is important when avoiding collisions.
So if md5() generates the most secure hash, why would you ever use the less secure crc32() and sha1
Crypto usage in PHP is simple, but that doesn’t mean it’s free. First off, depending on the data that you’re encrypting, you might have reasons to store a 32-bit value in the database instead of the 160-bit value to save on space. Second, the more secure the crypto is, the longer is the computation time to deliver the hash value. A high volume site might be significantly slowed down, if frequent md5() generation is required.
How do you match the character ^ at the beginning of the string?
^\^
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