Hive User Defined Functions

Hive User Defined Functions

Hive User Defined Functions (UDFs) fall into the following categories: (* )

1. Built-in Operators
   • Relational Operators
   • Arithmetic Operators
   • Logical Operators
   • Complex Type Constructors
   • Operators on Complex Types
2. Built-in Functions
   • Mathematical Functions
   • Collection Functions
   • Type Conversion Functions
   • Date Functions
   • Conditional Functions
   • String Functions
   • Misc. Functions
     • xpath
     • get_json_object
     • reflect
3. Built-in Aggregate Functions (UDAF)
4. Built-in Table-Generating Functions (UDTF)
   • explode
   • json_tuple

In the Karmasphere Analyst Query Window, use the commands below to show the latest documentation:

SHOW  FUNCTIONS;
DESCRIBE  FUNCTION <function_name>;

1. Built-in Operators

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	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 IS NULL	all types	TRUE if expression A evaluates to NULL otherwise FALSE
A IS NOT NULL	All types	TRUE if expression A evaluates to NULL otherwise FALSE
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, ...
array	(val1, val2, ...)	Creates an array with the given elements

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<K, V> 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.

2. 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
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 e^a 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 a^p
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
int double	positive(int a) positive(double a)	Returns a
int double	negative(int a) negative(double a)	Returns -a

Collection Functions

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

Return Type	Name(Signature)	Description
int	size(Map<K.V>)	Returns the number of elements in the map type
int	size(Array<T>)	Returns the number of elements in the array type

Type Conversion Functions

The following type conversion functions are supported in hive:

Return Type	Name(Signature)	Description
Expected "=" to follow "type"	cast(expr as <type>)	Converts the results of the expression expr to <type> 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:

string	from_unixtime(int unixtime)	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
int	date_add(string startdate, int days)	Add a number of days to startdate: date_add('2008-12-31', 1) = '2009-01-01'
int	date_sub(string startdate, int days)	Subtract a number of days to startdate: date_sub('2008-12-31', 1) = '2008-12-30'

Conditional Functions

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	length(string A)	Returns the length of the string
string	reverse(string A)	Returns the reversed string
string	concat(string A, string B...)	Returns the string resulting from concatenating the strings 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.
string	concat_ws(string SEP, string A, string B...)	Like concat() above, but with custom separator SEP.
string	substr(string A, int start) substring(string A, int start)	Returns the substring of A starting from start position till the end of string A e.g. concat('foobar', 4) results in 'bar' (see [http://dev.mysql.com/doc/refman/5.0/en/string-functions.html#function_substr ])
string	substr(string A, int start, int len) substring(string A, int start, int len)	Returns the substring of A starting from start position with length len e.g. concat('foobar', 4, 1) results in 'b' (see [http://dev.mysql.com/doc/refman/5.0/en/string-functions.html#function_substr ])
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'
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	trim(string A)	Returns the string resulting from trimming spaces from both ends of A e.g. trim(' foobar ') results in 'foobar'
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 '
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'
string	regexp_replace(string A, string B, string C)	Returns the string resulting from replacing all substrings in B that match the Java regular expression syntax(See Java regular expressions syntax) with C 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	regexp_extract(string subject, string pattern, int intex)	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.
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	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
string	space(int n)	Return a string of n spaces
string	repeat(string str, int n)	Repeat str n times
string	ascii(string str)	Returns the numeric value of the first character of str
string	lpad(string str, int len, string pad)	Returns str, left-padded with pad to a length of len
string	rpad(string str, int len, string pad)	Returns str, right-padded with pad to a length of len
array	split(string str, string pat)	Split str around pat (pat is a regular expression)
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
array<array<string>>	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") )
array<struct<string,double>>	ngrams(array<array<string>>, 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 Hive/StatisticsAndDataMining for more information.
array<struct<string,double>>	context_ngrams(array<array<string>>, array<string>, int K, int pf)	Returns the top-k contextual N-grams from a set of tokenized sentences, given a string of "context". See Hive/StatisticsAndDataMining for more information.

Misc. Functions

xpath

xpath, xpath_short, xpath_int, xpath_long, xpath_float, xpath_double, xpath_number, xpath_string

• Functions for parsing XML data using XPath expressions.
• Since version: 0.6.0

Overview

The xpath family of UDFs are wrappers around the Java XPath library javax.xml.xpath provided by the JDK. The library is based on the XPath 1.0 specification. Please refer to http://java.sun.com/javase/6/docs/api/javax/xml/xpath/package-summary.html for detailed information on the Java XPath library.

All functions follow the form: xpath_*(xml_string, xpath_expression_string). The XPath expression string is compiled and cached. It is reused if the expression in the next input row matches the previous. Otherwise, it is recompiled. So, the xml string is always parsed for every input row, but the xpath expression is precompiled and reused for the vast majority of use cases.

Backward axes are supported. For example:

 

 

SELECT xpath ('','/descendant::c/ancestor::b/@id') FROM t1 LIMIT 1 ; ["1","2"]

Each function returns a specific Hive type given the XPath expression:

• xpath returns a Hive array of strings.

• xpath_string returns a string.

• xpath_boolean returns a boolean.

• xpath_short returns a short integer.

• xpath_int returns an integer.

• xpath_long returns a long integer.

• xpath_float returns a floating point number.

• xpath_double,xpath_number returns a double-precision floating point number (xpath_number is an alias for xpath_double).

The UDFs are schema agnostic - no XML validation is performed. However, malformed xml (e.g., <a><b>1</b></aa>) will result in a runtime exception being thrown.

Following are specifics on each xpath UDF variant.

xpath

The xpath() function always returns a hive array of strings. If the expression results in a non-text value (e.g., another xml node) the function will return an empty array. There are 2 primary uses for this function: to get a list of node text values or to get a list of attribute values.

Examples:

Non-matching XPath expression:

 

SELECT xpath('<a><b>b1</b><b>b2</b></a>','a/*') FROM src LIMIT 1 ;

Returns: [] 

 

Get a list of node text values:

SELECT xpath('<a><b>b1</b><b>b2</b></a>','a/*/text()') FROM src LIMIT 1 ;

Returns: ["b1","b2"]

Get a list of values for attribute 'id':

SELECT xpath('b1b2','//@id') FROM src LIMIT 1 ; 

Returns: ["foo","bar"]

Get a list of node texts for nodes where the 'class' attribute equals 'bb':

SELECT xpath ('b1b2b3c1c2', 'a/*[@class="bb"]/text()') FROM src LIMIT 1 ;

Returns: ["b1","c1"]

xpath_string

The xpath_string() function returns the text of the first matching node.

Get the text for node 'a/b':

SELECT xpath_string ('<a><b>bb</b><c>cc</c></a>', 'a/b') FROM src LIMIT 1 ;

Returns: bb

Get the text for node 'a'. Because 'a' has children nodes with text, the result is a composite of text from the children.

SELECT xpath_string ('<a><b>bb</b><c>cc</c></a>', 'a') FROM src LIMIT 1 ;

Returns: bbcc

Non-matching expression returns an empty string:

SELECT xpath_string ('<a><b>bb</b><c>cc</c></a>', 'a/d') FROM src LIMIT 1 ;

Gets the text of the first node that matches '//b':

SELECT xpath_string ('<a><b>b1</b><b>b2</b></a>', '//b') FROM src LIMIT 1 ;

Returns: b1

Gets the second matching node:

SELECT xpath_string ('<a><b>b1</b><b>b2</b></a>', 'a/b[2]') FROM src LIMIT 1 ;

Returns: b2

Gets the text from the first node that has an attribute 'id' with value 'b_2':

SELECT xpath_string ('b1b2', 'a/b[@id="b_2"]') FROM src LIMIT 1 ;

Returns: b2

xpath_boolean

Returns true if the XPath expression evaluates to true, or if a matching node is found.

Match Found:

SELECT xpath_boolean ('<a><b>b</b></a>', 'a/b') FROM src LIMIT 1 ;

Returns: true

No Match Found:

SELECT  xpath_boolean ( '<a><b>b</b></a>', 'a/c') FROM src LIMIT 1 ;

Returns: false

Match found:

SELECT xpath_boolean ('<a><b>b</b></a>', 'a/b = "b"') FROM src LIMIT 1 ;

Returns: true

No match found:

SELECT  xpath_boolean ('<a><b>10</b></a>', 'a/b < 10') FROM src LIMIT  1 ;

Returns: false

xpath_short, xpath_int, xpath_long

These functions return an integer numeric value, or the value zero if no match is found, or a match is found but the value is non-numeric. Mathematical operations are supported. In cases where the value overflows the return type, then the maximum value for the type is returned.

No match:

SELECT

 xpath_int ('<a>b</a>', 'a = 10') FROM src LIMIT 1 ;

Returns: 0

Non-numeric match:

SELECT xpath_int ('<a>this is not a number</a>', 'a') FROM src LIMIT 1 ;

Returns: 0

SELECT xpath_int ('<a>this 2 is not a number</a>', 'a') FROM src LIMIT 1 ;

Returns: 0

Adding values:

SELECT   xpath_int ( '1248', 'sum(a/*)') FROM src LIMIT 1 ;

Returns: 15

SELECT  xpath_int ('1248', 'sum(a/b)') FROM src LIMIT 1 ;

Returns: 7

SELECT xpath_int ('1248', 'sum(a/b[@class="odd"])') FROM src LIMIT 1 ;

Returns: 5

Overflow:

SELECT xpath_int ('<a><b>2000000000</b><c>40000000000</c></a>', 'a/b * a/c') FROM src LIMIT 1 ;

Returns: 2147483647

xpath_float, xpath_double, xpath_number

Similar to xpath_short, xpath_int and xpath_long but with floating point semantics. Non-matches result in zero. However, non-numeric matches result in NaN. Note that xpath_number() is an alias for xpath_double().

No match:

SELECT xpath_double ('<a>b</a>', 'a = 10') FROM src LIMIT 1 ;	

Returns: 0.0

Non-numeric match:

SELECT xpath_double ('<a>this is not a number</a>', 'a') FROM src LIMIT 1 ;

Returns: NaN

A very large number:

SELECT xpath_double ('<a><b>2000000000</b><c>40000000000</c></a>', 'a/b * a/c')FROM src LIMIT 1 ;

Returns: 8.0E19

get_json_object

A limited version of JSONPath is supported:

• $ : Root object
• . : Child operator
• [] : Subscript operator for array
• * : Wildcard for []

Syntax not supported that's worth noticing:

• : Zero length string as key
• .. : Recursive descent
• @ : Current object/element
• () : Script expression
• ?() : Filter (script) expression.
• [,] : Union operator
• [start:end:step] : array slice operator

Example: src_json table is a single column (json), single row table:

/* json */

{"store":
  {"fruit":[{"weight":8,"type":"apple"},{"weight":9,"type":"pear"}],
   "bicycle":{"price":19.95,"color":"red"}
  },
 "email":"amy@only_for_json_udf_test.net",
 "owner":"amy"
}

The fields of the json object can be extracted using these queries:

SELECT get_json_object(src_json.json, '$.owner') FROM src_json;

Returns:  amy 

SELECT get_json_object(src_json.json, '$.store.fruit[0]') FROM src_json;

Returns: {"weight":8,"type":"apple"}

SELECT get_json_object(src_json.json, '$.non_exist_key') FROM src_json;

Returns: NULL

reflect

It is possible to use pre-existing Java functions as UDFs, using reflect. For example:

SELECT reflect("java.lang.Math", "ceil", 3.142) FROM newtable LIMIT 1;

SELECT reflect("java.lang.Math", "max", 5 , 10) FROM newtable LIMIT 1;

In the above example, the first argument to reflect is the class name, the second is the function name, and the third argument is a value that is passed to the function. Note that any number of arguments can be specified after the function name.

3. Built-in Aggregate Functions (UDAF)

The following are built-in aggregate functions are supported in Hive:

Return Type	Name(Signature)	Description
bigint	count(*), count(expr), count(DISTINCT expr[, expr...])	count(*) - Returns the total number of retrieved rows, including rows containing NULL values; count(expr) - Returns the number of rows for which the supplied expression is non-NULL; count(DISTINCT expr[, expr]) - Returns the number of rows for which the supplied expression(s) are unique and non-NULL.
double	sum(col), sum(DISTINCT col)	Returns the sum of the elements in the group or the sum of the distinct values of the column in the group
double	avg(col), avg(DISTINCT col)	Returns the average of the elements in the group or the average of the distinct values of the column in the group
double	min(col)	Returns the minimum of the column in the group
double	max(col)	Returns the maximum value of the column in the group
double	var_pop(col)	Returns the variance of a numeric column in the group
double	var_samp(col)	Returns the unbiased sample variance of a numeric column in the group
double	stddev_pop(col)	Returns the standard deviation of a numeric column in the group
double	stddev_samp(col)	Returns the unbiased sample standard deviation of a numeric column in the group
double	covar_pop(col1, col2)	Returns the population covariance of a pair of numeric columns in the group
double	covar_samp(col1, col2)	Returns the sample covariance of a pair of a numeric columns in the group
double	corr(col1, col2)	Returns the Pearson coefficient of correlation of a pair of a numeric columns in the group
double	percentile(col, p)	Returns the exact pth percentile of an integer column in the group (does not work with floating point types). p must be between 0 and 1.
array<double>	percentile(col, array(p1 [, p2 ]...))	Returns the exact percentiles p1 , p2 , ... of an integer column in the group (does not work with floating point types). pi must be between 0 and 1.
double	percentile_approx(col, p [, B])	Returns an approximate pth percentile of a numeric column (including floating point types) in the group. The B parameter controls approximation accuracy at the cost of memory. Higher values yield better approximations, and the default is 10,000. When the number of distinct values in col is smaller than B, this gives an exact percentile value.
array<double>	percentile_approx(col, array(p1 [, p2 ]...) [, B])	Same as above, but accepts and returns an array of percentile values instead of a single one.
array<struct {'x','y'}>	histogram_numeric(col, b)	Computes a histogram of a numeric column in the group using b non-uniformly spaced bins. The output is an array of size b of double-valued (x,y) coordinates that represent the bin centers and heights

4. Built-in Table-Generating Functions (UDTF)

Normal user-defined functions, such as concat(), take in a single input row and output a single output row. In contrast, table-generating functions transform a single input row to multiple output rows.

explode

explode() takes in an array as an input and outputs the elements of the array as separate rows. UDTF's can be used in the SELECT expression list and as a part of LATERAL VIEW.

An example use of explode() in the SELECT expression list is as follows:

Consider a table named myTable that has a single column (myCol) and two rows:

Array<int> myCol

[1,2,3]

[4,5,6]

Then running the query:

SELECT explode(myCol) AS myNewCol FROM myTable;

Will produce:

int myNewCol

1

2

3

4

5

6

Using the syntax "SELECT udtf(col) AS colAlias..." has a few limitations:

• No other expressions are allowed in SELECT
  • SELECT pageid, explode(adid_list) AS myCol... is not supported
• UDTF's can't be nested
  • SELECT explode(explode(adid_list)) AS myCol... is not supported
• GROUP BY / CLUSTER BY / DISTRIBUTE BY / SORT BY is not supported
  • SELECT explode(adid_list) AS myCol ... GROUP BY myCol is not supported

Please see Hive/LanguageManual/LateralView for an alternative syntax that does not have these limitations.

The following are built-in table-generating functions are supported in Hive:

Return Type	Name(Signature)	Description
myType	explode(array<myType> a)	For each element in a, explode() generates a row containing that element

json_tuple

A new json_tuple() UDTF is introduced in hive 0.7. It takes a set of names (keys) and return a tuple of values in one function. If you are using get_json_object() and want to replace it with json_tuple, the only changes is that your query will be using json_tuple() in lateral view rather than multiple get_json_object() in the select clause.

For example,

SELECT a.timestamp, get_json_object(a.appevents, '$.eventid'),     get_json_object(a.appenvets, '$.eventname') ROM log a;

should be changed to

SELECT a.timestamp, b.* FROM log a lateral VIEW json_tuple(a.appevent, 'eventid', 'eventname') b AS f1, f2;

 

 

转：http://www.karmasphere.com/Karmasphere-Analyst/hive-user-defined-functions.html

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Note: sections of this reference material are derived from the Hive project from the Apache Foundation , specifically from this wiki .