hive udf

Relational Operators

The following operators compare the passed operands and generate a TRUE or FALSE value depending on whether the comparison between the operands holds.

Operator	Operand types	Description
A = B	All primitive types	TRUE if expression A is equal to expression B otherwise FALSE
A <=> B	All primitive types	Returns same result with EQUAL(=) operator for non-null operands, but returns TRUE if both are NULL, FALSE if one of the them is NULL (as of version 0.9.0)
A == B	None!	Fails because of invalid syntax. SQL uses =, not ==
A <> B	All primitive types	NULL if A or B is NULL, TRUE if expression A is NOT equal to expression B otherwise FALSE
A < B	All primitive types	NULL if A or B is NULL, TRUE if expression A is less than expression B otherwise FALSE
A <= B	All primitive types	NULL if A or B is NULL, TRUE if expression A is less than or equal to expression B otherwise FALSE
A > B	All primitive types	NULL if A or B is NULL, TRUE if expression A is greater than expression B otherwise FALSE
A >= B	All primitive types	NULL if A or B is NULL, TRUE if expression A is greater than or equal to expression B otherwise FALSE
A [NOT] BETWEEN B AND C	All primitive types	NULL if A, B or C is NULL, TRUE if A is greater than or equal to B AND A less than or equal to C otherwise FALSE. This can be inverted by using the NOT keyword. (as of version 0.9.0)
A IS NULL	all types	TRUE if expression A evaluates to NULL otherwise FALSE
A IS NOT NULL	All types	FALSE if expression A evaluates to NULL otherwise TRUE
A LIKE B	strings	NULL if A or B is NULL, TRUE if string A matches the SQL simple regular expression B, otherwise FALSE. The comparison is done character by character. The _ character in B matches any character in A(similar to . in posix regular expressions) while the % character in B matches an arbitrary number of characters in A(similar to .* in posix regular expressions) e.g. 'foobar' like 'foo' evaluates to FALSE where as 'foobar' like 'foo_ _ _' evaluates to TRUE and so does 'foobar' like 'foo%'
A RLIKE B	strings	NULL if A or B is NULL, TRUE if string A matches the Java regular expression B(See Java regular expressions syntax), otherwise FALSE e.g. 'foobar' rlike 'foo' evaluates to FALSE where as 'foobar' rlike '^f.*r$' evaluates to TRUE
A REGEXP B	strings	Same as RLIKE

Arithmetic Operators

The following operators support various common arithmetic operations on the operands. All return number types; if any of the operands are NULL, then the result is also NULL.

Operator	Operand types	Description
A + B	All number types	Gives the result of adding A and B. The type of the result is the same as the common parent(in the type hierarchy) of the types of the operands. e.g. since every integer is a float, therefore float is a containing type of integer so the + operator on a float and an int will result in a float.
A - B	All number types	Gives the result of subtracting B from A. The type of the result is the same as the common parent(in the type hierarchy) of the types of the operands.
A * B	All number types	Gives the result of multiplying A and B. The type of the result is the same as the common parent(in the type hierarchy) of the types of the operands. Note that if the multiplication causing overflow, you will have to cast one of the operators to a type higher in the type hierarchy.
A / B	All number types	Gives the result of dividing B from A. The result is a double type.
A % B	All number types	Gives the reminder resulting from dividing A by B. The type of the result is the same as the common parent(in the type hierarchy) of the types of the operands.
A & B	All number types	Gives the result of bitwise AND of A and B. The type of the result is the same as the common parent(in the type hierarchy) of the types of the operands.
A | B	All number types	Gives the result of bitwise OR of A and B. The type of the result is the same as the common parent(in the type hierarchy) of the types of the operands.
A ^ B	All number types	Gives the result of bitwise XOR of A and B. The type of the result is the same as the common parent(in the type hierarchy) of the types of the operands.
~A	All number types	Gives the result of bitwise NOT of A. The type of the result is the same as the type of A.

Logical Operators

The following operators provide support for creating logical expressions. All of them return boolean TRUE, FALSE, or NULL depending upon the boolean values of the operands. NULL behaves as an "unknown" flag, so if the result depends on the state of an unknown, the result itself is unknown.

Operator	Operand types	Description
A AND B	boolean	TRUE if both A and B are TRUE, otherwise FALSE. NULL if A or B is NULL
A && B	boolean	Same as A AND B
A OR B	boolean	TRUE if either A or B or both are TRUE; FALSE OR NULL is NULL; otherwise FALSE
A || B	boolean	Same as A OR B
NOT A	boolean	TRUE if A is FALSE or NULL if A is NULL. Otherwise FALSE.
! A	boolean	Same as NOT A

Complex Type Constructors

The following functions construct instances of complex types.

Constructor Function	Operands	Description
map	(key1, value1, key2, value2, ...)	Creates a map with the given key/value pairs
struct	(val1, val2, val3, ...)	Creates a struct with the given field values. Struct field names will be col1, col2, ...
named_struct	(name1, val1, name2, val2, ...)	Creates a struct with the given field names and values.
array	(val1, val2, ...)	Creates an array with the given elements
create_union	(tag, val1, val2, ...)	Creates a union type with the value that is being pointed to by the tag parameter

Operators on Complex Types

The following operators provide mechanisms to access elements in Complex Types

Operator	Operand types	Description
A[n]	A is an Array and n is an int	Returns the nth element in the array A. The first element has index 0 e.g. if A is an array comprising of ['foo', 'bar'] then A[0] returns 'foo' and A[1] returns 'bar'
M[key]	M is a Map and key has type K	Returns the value corresponding to the key in the map e.g. if M is a map comprising of {'f' -> 'foo', 'b' -> 'bar', 'all' -> 'foobar'} then M['all'] returns 'foobar'
S.x	S is a struct	Returns the x field of S. e.g for struct foobar {int foo, int bar} foobar.foo returns the integer stored in the foo field of the struct.

Built-in Functions

Mathematical Functions

The following built-in mathematical functions are supported in hive; most return NULL when the argument(s) are NULL:

Return Type	Name(Signature)	Description
BIGINT	round(double a)	Returns the rounded BIGINT value of the double
DOUBLE	round(double a, int d)	Returns the double rounded to d decimal places
BIGINT	floor(double a)	Returns the maximum BIGINT value that is equal or less than the double
BIGINT	ceil(double a), ceiling(double a)	Returns the minimum BIGINT value that is equal or greater than the double
double	rand(), rand(int seed)	Returns a random number (that changes from row to row) that is distributed uniformly from 0 to 1. Specifiying the seed will make sure the generated random number sequence is deterministic.
double	exp(double a)	Returns ea where e is the base of the natural logarithm
double	ln(double a)	Returns the natural logarithm of the argument
double	log10(double a)	Returns the base-10 logarithm of the argument
double	log2(double a)	Returns the base-2 logarithm of the argument
double	log(double base, double a)	Return the base "base" logarithm of the argument
double	pow(double a, double p) power(double a, double p)	Return ap
double	sqrt(double a)	Returns the square root of a
string	bin(BIGINT a)	Returns the number in binary format (see [http://dev.mysql.com/doc/refman/5.0/en/string-functions.html#function_bin])
string	hex(BIGINT a) hex(string a)	If the argument is an int, hex returns the number as a string in hex format. Otherwise if the number is a string, it converts each character into its hex representation and returns the resulting string. (see [http://dev.mysql.com/doc/refman/5.0/en/string-functions.html#function_hex])
string	unhex(string a)	Inverse of hex. Interprets each pair of characters as a hexidecimal number and converts to the character represented by the number.
string	conv(BIGINT num, int from_base, int to_base)	Converts a number from a given base to another (see [http://dev.mysql.com/doc/refman/5.0/en/mathematical-functions.html#function_conv])
double	abs(double a)	Returns the absolute value
int double	pmod(int a, int b) pmod(double a, double b)	Returns the positive value of a mod b
double	sin(double a)	Returns the sine of a (a is in radians)
double	asin(double a)	Returns the arc sin of x if -1<=a<=1 or null otherwise
double	cos(double a)	Returns the cosine of a (a is in radians)
double	acos(double a)	Returns the arc cosine of x if -1<=a<=1 or null otherwise
double	tan(double a)	Returns the tangent of a (a is in radians)
double	atan(double a)	Returns the arctangent of a
double	degrees(double a)	Converts value of a from radians to degrees
double	radians(double a)	Converts value of a from degrees to radians
int double	positive(int a) positive(double a)	Returns a
int double	negative(int a) negative(double a)	Returns -a
float	sign(double a)	Returns the sign of a as '1.0' or '-1.0'
double	e()	Returns the value of e
double	pi()	Returns the value of pi

Collection Functions

The following built-in collection functions are supported in hive:

Return Type	Name(Signature)	Description
int	size(Map)	Returns the number of elements in the map type
int	size(Array)	Returns the number of elements in the array type
array	map_keys(Map)	Returns an unordered array containing the keys of the input map
array	map_values(Map)	Returns an unordered array containing the values of the input map
boolean	array_contains(Array, value)	Returns TRUE if the array contains value
array	sort_array(Array)	Sorts the input array in ascending order according to the natural ordering of the array elements and returns it (as of version 0.9.0)

Type Conversion Functions

The following type conversion functions are supported in hive:

Return Type	Name(Signature)	Description
binary	binary(string|binary)	Casts the parameter into a binary
Expected "=" to follow "type"	cast(expr as )	Converts the results of the expression expr to e.g. cast('1' as BIGINT) will convert the string '1' to it integral representation. A null is returned if the conversion does not succeed.

Date Functions

The following built-in date functions are supported in hive:

Return Type	Name(Signature)	Description
string	from_unixtime(bigint unixtime[, string format])	Converts the number of seconds from unix epoch (1970-01-01 00:00:00 UTC) to a string representing the timestamp of that moment in the current system time zone in the format of "1970-01-01 00:00:00"
bigint	unix_timestamp()	Gets current time stamp using the default time zone.
bigint	unix_timestamp(string date)	Converts time string in format yyyy-MM-dd HH:mm:ss to Unix time stamp, return 0 if fail: unix_timestamp('2009-03-20 11:30:01') = 1237573801
bigint	unix_timestamp(string date, string pattern)	Convert time string with given pattern (see [http://java.sun.com/j2se/1.4.2/docs/api/java/text/SimpleDateFormat.html]) to Unix time stamp, return 0 if fail: unix_timestamp('2009-03-20', 'yyyy-MM-dd') = 1237532400
string	to_date(string timestamp)	Returns the date part of a timestamp string: to_date("1970-01-01 00:00:00") = "1970-01-01"
int	year(string date)	Returns the year part of a date or a timestamp string: year("1970-01-01 00:00:00") = 1970, year("1970-01-01") = 1970
int	month(string date)	Returns the month part of a date or a timestamp string: month("1970-11-01 00:00:00") = 11, month("1970-11-01") = 11
int	day(string date) dayofmonth(date)	Return the day part of a date or a timestamp string: day("1970-11-01 00:00:00") = 1, day("1970-11-01") = 1
int	hour(string date)	Returns the hour of the timestamp: hour('2009-07-30 12:58:59') = 12, hour('12:58:59') = 12
int	minute(string date)	Returns the minute of the timestamp
int	second(string date)	Returns the second of the timestamp
int	weekofyear(string date)	Return the week number of a timestamp string: weekofyear("1970-11-01 00:00:00") = 44, weekofyear("1970-11-01") = 44
int	datediff(string enddate, string startdate)	Return the number of days from startdate to enddate: datediff('2009-03-01', '2009-02-27') = 2
string	date_add(string startdate, int days)	Add a number of days to startdate: date_add('2008-12-31', 1) = '2009-01-01'
string	date_sub(string startdate, int days)	Subtract a number of days to startdate: date_sub('2008-12-31', 1) = '2008-12-30'
timestamp	from_utc_timestamp(timestamp, string timezone)	Assumes given timestamp ist UTC and converts to given timezone (as of Hive 0.8.0)
timestamp	to_utc_timestamp(timestamp, string timezone)	Assumes given timestamp is in given timezone and converts to UTC (as of Hive 0.8.0)

Conditional Functions

Return Type	Name(Signature)	Description
T	if(boolean testCondition, T valueTrue, T valueFalseOrNull)	Return valueTrue when testCondition is true, returns valueFalseOrNull otherwise
T	COALESCE(T v1, T v2, ...)	Return the first v that is not NULL, or NULL if all v's are NULL
T	CASE a WHEN b THEN c [WHEN d THEN e]* [ELSE f] END	When a = b, returns c; when a = d, return e; else return f
T	CASE WHEN a THEN b [WHEN c THEN d]* [ELSE e] END	When a = true, returns b; when c = true, return d; else return e

String Functions

The following are built-in String functions are supported in hive:

Return Type	Name(Signature)	Description
int	ascii(string str)	Returns the numeric value of the first character of str
string	concat(string|binary A, string|binary B...)	Returns the string or bytes resulting from concatenating the strings or bytes passed in as parameters in order. e.g. concat('foo', 'bar') results in 'foobar'. Note that this function can take any number of input strings.
array>	context_ngrams(array>, array, int K, int pf)	Returns the top-k contextual N-grams from a set of tokenized sentences, given a string of "context". See StatisticsAndDataMining for more information.
string	concat_ws(string SEP, string A, string B...)	Like concat() above, but with custom separator SEP.
string	concat_ws(string SEP, array)	Like concat_ws() above, but taking an array of strings. (as of Hive 0.9.0)
int	find_in_set(string str, string strList)	Returns the first occurance of str in strList where strList is a comma-delimited string. Returns null if either argument is null. Returns 0 if the first argument contains any commas. e.g. find_in_set('ab', 'abc,b,ab,c,def') returns 3
string	format_number(number x, int d)	Formats the number X to a format like '#,###,###.##', rounded to D decimal places, and returns the result as a string. If D is 0, the result has no decimal point or fractional part. (as of Hive 0.10.0)
string	get_json_object(string json_string, string path)	Extract json object from a json string based on json path specified, and return json string of the extracted json object. It will return null if the input json string is invalid. NOTE: The json path can only have the characters [0-9a-z_], i.e., no upper-case or special characters. Also, the keys *cannot start with numbers.* This is due to restrictions on Hive column names.
boolean	in_file(string str, string filename)	Returns true if the string str appears as an entire line in filename.
int	instr(string str, string substr)	Returns the position of the first occurence of substr in str
int	length(string A)	Returns the length of the string
int	locate(string substr, string str[, int pos])	Returns the position of the first occurrence of substr in str after position pos
string	lower(string A) lcase(string A)	Returns the string resulting from converting all characters of B to lower case e.g. lower('fOoBaR') results in 'foobar'
string	lpad(string str, int len, string pad)	Returns str, left-padded with pad to a length of len
string	ltrim(string A)	Returns the string resulting from trimming spaces from the beginning(left hand side) of A e.g. ltrim(' foobar ') results in 'foobar '
array>	ngrams(array>, int N, int K, int pf)	Returns the top-k N-grams from a set of tokenized sentences, such as those returned by the sentences() UDAF. See StatisticsAndDataMining for more information.
string	parse_url(string urlString, string partToExtract [, string keyToExtract])	Returns the specified part from the URL. Valid values for partToExtract include HOST, PATH, QUERY, REF, PROTOCOL, AUTHORITY, FILE, and USERINFO. e.g. parse_url('http://facebook.com/path1/p.php?k1=v1&k2=v2#Ref1', 'HOST') returns 'facebook.com'. Also a value of a particular key in QUERY can be extracted by providing the key as the third argument, e.g. parse_url('http://facebook.com/path1/p.php?k1=v1&k2=v2#Ref1', 'QUERY', 'k1') returns 'v1'.
string	printf(String format, Obj... args)	Returns the input formatted according do printf-style format strings (as of Hive 0.9.0)
string	regexp_extract(string subject, string pattern, int index)	Returns the string extracted using the pattern. e.g. regexp_extract('foothebar', 'foo(.*?)(bar)', 2) returns 'bar.' Note that some care is necessary in using predefined character classes: using '\s' as the second argument will match the letter s; ' s' is necessary to match whitespace, etc. The 'index' parameter is the Java regex Matcher group() method index. See docs/api/java/util/regex/Matcher.html for more information on the 'index' or Java regex group() method.
string	regexp_replace(string INITIAL_STRING, string PATTERN, string REPLACEMENT)	Returns the string resulting from replacing all substrings in INITIAL_STRING that match the java regular expression syntax defined in PATTERN with instances of REPLACEMENT, e.g. regexp_replace("foobar", "oo|ar", "") returns 'fb.' Note that some care is necessary in using predefined character classes: using '\s' as the second argument will match the letter s; ' s' is necessary to match whitespace, etc.
string	repeat(string str, int n)	Repeat str n times
string	reverse(string A)	Returns the reversed string
string	rpad(string str, int len, string pad)	Returns str, right-padded with pad to a length of len
string	rtrim(string A)	Returns the string resulting from trimming spaces from the end(right hand side) of A e.g. rtrim(' foobar ') results in ' foobar'
array>	sentences(string str, string lang, string locale)	Tokenizes a string of natural language text into words and sentences, where each sentence is broken at the appropriate sentence boundary and returned as an array of words. The 'lang' and 'locale' are optional arguments. e.g. sentences('Hello there! How are you?') returns ( ("Hello", "there"), ("How", "are", "you") )
string	space(int n)	Return a string of n spaces
array	split(string str, string pat)	Split str around pat (pat is a regular expression)
map	str_to_map(text[, delimiter1, delimiter2])	Splits text into key-value pairs using two delimiters. Delimiter1 separates text into K-V pairs, and Delimiter2 splits each K-V pair. Default delimiters are ',' for delimiter1 and '=' for delimiter2.
string	substr(string|binary A, int start) substring(string|binary A, int start)	Returns the substring or slice of the byte array of A starting from start position till the end of string A e.g. substr('foobar', 4) results in 'bar' (see [http://dev.mysql.com/doc/refman/5.0/en/string-functions.html#function_substr])
string	substr(string|binary A, int start, int len) substring(string|binary A, int start, int len)	Returns the substring or slice of the byte array of A starting from start position with length len e.g. substr('foobar', 4, 1) results in 'b' (see [http://dev.mysql.com/doc/refman/5.0/en/string-functions.html#function_substr])
string	translate(string input, string from, string to)	Translates the input string by replacing the characters present in the from string with the corresponding characters in the to string. This is similar to the translate function in PostgreSQL. If any of the parameters to this UDF are NULL, the result is NULL as well (available as of Hive 0.10.0)
string	trim(string A)	Returns the string resulting from trimming spaces from both ends of A e.g. trim(' foobar ') results in 'foobar'
string	upper(string A) ucase(string A)	Returns the string resulting from converting all characters of A to upper case e.g. upper('fOoBaR') results in 'FOOBAR'

Misc. Functions

Return Type	Name(Signature)	Description
varies	java_method(class, method[, arg1[, arg2..]])	Synonym for reflect (as of Hive 0.9.0)
varies	reflect(class, method[, arg1[, arg2..]])	Use this UDF to call Java methods by matching the argument signature (uses reflection). (as of Hive 0.7.0)

xpath

Pig Basics

Pig raises the level of abstraction for processing large datasets. MapReduce allows you, as the programmer, to specify a map function followed by a reduce function, but working out how to fit your data processing into this pattern, which often requires multiple MapReduce stages, can be a challenge. With Pig, the data structures are much richer, typically being multivalued and nested, and the set of transformations you can apply to the data are much more powerful.

Pig is made up of two pieces:

• The language used to express data flows, called Pig Latin.

• The execution environment to run Pig Latin programs. There are currently two environments: local execution in a single JVM and distributed execution on a Hadoop cluster.

A Pig Latin program is made up of a series of operations, or transformations, that are applied to the input data to produce output. Taken as a whole, the operations describe a data flow, which the Pig execution environment translates into an executable representation and then runs. Under the covers, Pig turns the transformations into a series of MapReduce jobs

Installing and Running Pig

Download latest version of Pig from the following link (Pig Installation).

$ tar xzf pig-0.7.0.tar.gz

set pig environment variables

$ export PIG_INSTALL=/home/user1/pig-0.7.0.tar.gz

$ export PATH=$PATH:$PIG_INSTALL/bin

You also need to set the JAVA_HOME environment variable to point to a suitable Java installation.

Pig has two execution types or modes: 

1) local mode : Pig runs in a single JVM and accesses the local filesystem. This mode is suitable only for small datasets.

$ pig -x local

grunt>

This starts Grunt, the Pig interactive shell

2) MapReduce mode : In MapReduce mode, Pig translates queries into MapReduce jobs and runs them on a Hadoop cluster. The cluster may be a pseudo- or fully distributed cluster.

set the HADOOP_HOME environment variable for finding which Hadoop client to run.

$ pig  or $ pig -x mapreduce , runs pig in MapReduce mode

Running Pig Programs

There are three ways of executing Pig programs, all of which work in both local and MapReduce mode

Script : Pig can run a script file that contains Pig commands. For example, pig

script.pig runs the commands in the local file script.pig

$ pig script.pig

Grunt : Grunt is an interactive shell for running Pig commands.It is also possible to run Pig scripts from within Grunt using run and exec.

Embedded :

You can run Pig programs from Java using the PigServer class, much like you can use JDBC to run SQL programs from Java.

PigPen is an Eclipse plug-in that provides an environment for developing Pig programs.

PigTools and EditorPlugins for pig can be downloaded from PigTools

Example of Pig in Interactive Mode (Grunt)

max_cgpa.pig

-- max_cgpa.pig: Finds the maximum cgpa of a user

records = LOAD 'pigsample.txt'

AS (name:chararray, spl:chararray, cgpa:float);

filtered_records = FILTER records BY cgpa > 0 AND cgpa < 10;

grouped_records = GROUP filtered_records BY spl;

max_cgpa = FOREACH grouped_records GENERATE group, MAX(filtered_records.cgpa);

STORE max_cgpa INTO 'output/cgpa_out';

Above pig script finds the maximum cgpa of a specialization.

pigsample.txt  ( Input to the pig )

raghu     ece     9

kumar    cse      8.5

biju       ece      8

mukul    cse      8.6

ashish   ece      7.0

subha    cse      8.3

ramu     ece     -8.3

rahul     cse      11.4

budania ece      5.4

first column represents name , second column specialization and third column is cgpa, by default each column is separated by tab space.

$ pig max_cgpa.pig

Output : 

(cse,8.6F)

(ece,9.0F)

Analysis : 

Statement : 1

records = LOAD 'pigsample.txt'AS (name:chararray, spl:chararray, cgpa:float);

Load input file in to memory from the file system (HDFS or local or Amazon S3). name:chararray notation describes the field’s

name and type; chararray is like a Java string, and an float is like a Java float.

grunt> DUMP records;

(raghu,ece,9.0F)

(kumar,cse,8.5F)

(biju,ece,8.0F)

(mukul,cse,8.6F)

(ashish,ece,7.0F)

(subha,cse,8.3F)

(ramu,ece,-8.3F)

(rahul,cse,11.4F)

(budania,ece,5.4F)

Input is converted in to a tuple , and each column is separated by ,

grunt> DESCRIBE records;

records: {name: chararray,spl: chararray,cgpa: float}

Statement : 2

filtered_records = FILTER records BY cgpa > 0 AND cgpa < 10;

grunt> DUMP filtered_records;

filter all the records whose cgpa <0 and="and" negative="negative">10 

(raghu,ece,9.0F)

(kumar,cse,8.5F)

(biju,ece,8.0F)

(mukul,cse,8.6F)

(ashish,ece,7.0F)

(subha,cse,8.3F)

(budania,ece,5.4F)

grunt> DESCRIBE filtered_records;

filtered_records: {name: chararray,spl: chararray,cgpa: float}

Statement : 3

The third statement uses the GROUP function to group the records relation by the specialization field.

grouped_records = GROUP filtered_records BY spl;

grunt> DUMP  grouped_records ;

(cse,{(kumar,cse,8.5F),(mukul,cse,8.6F),(subha,cse,8.3F)})

(ece,{(raghu,ece,9.0F),(biju,ece,8.0F),(ashish,ece,7.0F),(budania,ece,5.4F)})

grunt> DESCRIBE  grouped_records;

grouped_records: {group: chararray,filtered_records: {name: chararray,spl: chararray,cgpa: float}}

We now have two rows, or tuples, one for each specialization in the input data. The first field in each tuple is the field being grouped by (the specialization), and the second field is a bag of tuples

for that  specialization. A bag is just an unordered collection of tuples, which in Pig Latin is represented using curly braces.

By grouping the data in this way, we have created a row per  specialization , so now all that remains is to find the maximum cgpa for the tuples in each bag.

Statement : 4

max_cgpa = FOREACH grouped_records GENERATE group,

MAX(filtered_records.cgpa);

FOREACH processes every row to generate a derived set of rows, using a GENERATE clause to define the fields in each derived row. In this example, the first field is group, which is just the specialization. The second field is a little more complex.

The filtered_records.cgpa reference is to the cgpa field of the

filtered_records bag in the grouped_records relation. MAX is a built-in function for calculating the maximum value of fields in a bag. In this case, it calculates the maximum cgpa for the fields in each filtered_records bag.

grunt> DUMP    max_cgpa  ;

(cse,8.6F)

(ece,9.0F)

grunt> DESCRIBE    max_cgpa  ;

max_cgpa : {group: chararray,float}

Statement : 5

STORE max_cgpa INTO 'output/cgpa_out'

This command redirects the output of the script to a file (Local or HDFS) instead of printing the output on the console .

we’ve successfully calculated the maximum cgpa for each specialization.

With the ILLUSTRATE operator, Pig provides a tool for generating a reasonably complete and concise sample dataset.

--------------------------------------------------------------------

| records     | name: bytearray | spl: bytearray | cgpa: bytearray | 

--------------------------------------------------------------------

|             | kumar           | cse            | 8.5             | 

|             | mukul           | cse            | 8.6             | 

|             | ramu            | ece            | -8.3            | 

--------------------------------------------------------------------

----------------------------------------------------------------

| records     | name: chararray | spl: chararray | cgpa: float | 

----------------------------------------------------------------

|             | kumar           | cse            | 8.5         | 

|             | mukul           | cse            | 8.6         | 

|             | ramu            | ece            | -8.3        | 

----------------------------------------------------------------

-------------------------------------------------------------------------

| filtered_records     | name: chararray | spl: chararray | cgpa: float | 

-------------------------------------------------------------------------

|                      | kumar           | cse            | 8.5         | 

|                      | mukul           | cse            | 8.6         | 

-------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------------------

| grouped_records     | group: chararray | filtered_records: bag({name: chararray,spl: chararray,cgpa: float}) | 

----------------------------------------------------------------------------------------------------------------

|                     | cse              | {(kumar, cse, 8.5), (mukul, cse, 8.6)}                              | 

----------------------------------------------------------------------------------------------------------------

-------------------------------------------

|  max_cgpa   | group: chararray | float | 

-------------------------------------------

|              | cse              | 8.6   |

EXPLAIN max_cgpa  

Use the above command to see the logical and physical plans created by Pig.

Delete a temp table in sql server if it already exists

 
IF OBJECT_ID('tempdb..##tmp') IS NOT NULL 
begin
DROP TABLE ##tmp
end
CREATE TABLE ##tmp  
( TableName varchar(255),DifferenceInCounts int ) 

Date Functions in Hive

Date data types do not exist in Hive. In fact the dates are treated as strings in Hive. The date functions are listed below.

UNIX_TIMESTAMP()
This function returns the number of seconds from the Unix epoch (1970-01-01 00:00:00 UTC) using the default time zone.

UNIX_TIMESTAMP( string date )
This function converts the date in format 'yyyy-MM-dd HH:mm:ss' into Unix timestamp. This will return the number of seconds between the specified date and the Unix epoch. If it fails, then it returns 0.
Example: UNIX_TIMESTAMP('2000-01-01 00:00:00') returns 946713600

UNIX_TIMESTAMP( string date, string pattern )
This function converts the date to the specified date format and returns the number of seconds between the specified date and Unix epoch. If it fails, then it returns 0.
Example: UNIX_TIMESTAMP('2000-01-01 10:20:30','yyyy-MM-dd') returns 946713600

FROM_UNIXTIME( bigint number_of_seconds  [, string format] )
The FROM_UNIX function converts the specified number of seconds from Unix epoch and returns the date in the format 'yyyy-MM-dd HH:mm:ss'.
Example: FROM_UNIXTIME( UNIX_TIMESTAMP() ) returns the current date including the time. This is equivalent to the SYSDATE in oracle.

TO_DATE( string timestamp )
The TO_DATE function returns the date part of the timestamp in the format 'yyyy-MM-dd'.
Example: TO_DATE('2000-01-01 10:20:30') returns '2000-01-01'

YEAR( string date )
The YEAR function returns the year part of the date.
Example: YEAR('2000-01-01 10:20:30') returns 2000

MONTH( string date )
The MONTH function returns the month part of the date.
Example: YEAR('2000-03-01 10:20:30') returns 3

DAY( string date ), DAYOFMONTH( date )
The DAY or DAYOFMONTH function returns the day part of the date.
Example: DAY('2000-03-01 10:20:30') returns 1

HOUR( string date )
The HOUR function returns the hour part of the date.
Example: HOUR('2000-03-01 10:20:30') returns 10

MINUTE( string date )
The MINUTE function returns the minute part of the timestamp.
Example: MINUTE('2000-03-01 10:20:30') returns 20

SECOND( string date )
The SECOND function returns the second part of the timestamp.
Example: SECOND('2000-03-01 10:20:30') returns 30

WEEKOFYEAR( string date )
The WEEKOFYEAR function returns the week number of the date.
Example: WEEKOFYEAR('2000-03-01 10:20:30') returns 9

DATEDIFF( string date1, string date2 )
The DATEDIFF function returns the number of days between the two given dates.
Example: DATEDIFF('2000-03-01', '2000-01-10')  returns 51

DATE_ADD( string date, int days )
The DATE_ADD function adds the number of days to the specified date
Example: DATE_ADD('2000-03-01', 5) returns '2000-03-06'

DATE_SUB( string date, int days )
The DATE_SUB function subtracts the number of days to the specified date
Example: DATE_SUB('2000-03-01', 5) returns ‘2000-02-25’