THIS IS A TEST INSTANCE. ALL YOUR CHANGES WILL BE LOST!!!!
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= Hive User Defined Functions =
{toc}
In the CLI, use the commands below to show the latest documentation:
{code}
SHOW FUNCTIONS;
DESCRIBE FUNCTION <function_name>;
{code}
h2. Built-in Operators
h3. 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 |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 |
h3. 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. |
h3. 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 |
h3. 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|
h3. 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. |
h2. Built-in Functions
h3. 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 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 |
h3. 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 |
h3. 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. |
h3. Date Functions
The following built-in date functions are supported in hive:
|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 |
|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' |
h3. 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 |
h3. 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. substr('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. substr('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 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 |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. *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. |
|string |space(int n) |Return a string of n spaces |
|string |repeat(string str, int n) |Repeat str n times |
|int |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.|
h3. Misc. Functions
h4. xpath
The following functions are described in [Hive-LanguageManual-XPathUDF]:
* xpath, xpath_short, xpath_int, xpath_long, xpath_float, xpath_double, xpath_number, xpath_string
h4. 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:
{code}
+----+
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"
}
+----+
{code}
The fields of the json object can be extracted using these queries:
{code}
hive> SELECT get_json_object(src_json.json, '$.owner') FROM src_json;
amy
hive> SELECT get_json_object(src_json.json, '$.store.fruit[0]') FROM src_json;
{"weight":8,"type":"apple"}
hive> SELECT get_json_object(src_json.json, '$.non_exist_key') FROM src_json;
NULL
{code}
h2. 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 p^th^ 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(p~1,, [, p,,2,,]...)) | Returns the exact percentiles p,,1,,, p,,2,,, ... of an integer column in the group (does not work with floating point types). p,,i~ must be between 0 and 1. |
|double |percentile_approx(col, p [, B]) | Returns an approximate p^th^ 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(p~1,, [, p,,2_]...) [, 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 |
|array |collect_set(col) |Returns a set of objects with duplicate elements eliminated |
h2. Built-in Table-Generating Functions (UDTF)
<<Anchor(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.
h3. 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) <<Anchor(explode)>> |For each element in a, explode() generates a row containing that element |
h3. 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,
{code}
select a.timestamp, get_json_object(a.appevents, '$.eventid'), get_json_object(a.appenvets, '$.eventname') from log a;
{code}
should be changed to
{code}
select a.timestamp, b.*
from log a lateral view json_tuple(a.appevent, 'eventid', 'eventname') b as f1, f2;
{code}
h2. GROUPing and SORTing on f(column)
A typical OLAP pattern is that you have a timestamp column and you want to group by daily or other less granular date windows than by second. So you might want to select concat(year(dt),month(dt)) and then group on that concat(). But if you attempt to GROUP BY or SORT BY a column on which you've applied a function and alias, like this:
{code}
select f(col) as fc, count(*) from table_name group by fc
{code}
You will get an error:
{code}
FAILED: Error in semantic analysis: line 1:69 Invalid Table Alias or Column Reference fc
{code}
Because you are not able to GROUP BY or SORT BY a column alias on which a function has been applied. There are two workarounds. First, you can reformulate this query with subqueries, which is somewhat complicated:
{code}
select sq.fc,col1,col2,...,colN,count(*) from
(select f(col) as fc,col1,col2,...,colN from table_name) sq
group by sq.fc,col1,col2,...,colN
{code}
Or you can make sure not to use a column alias, which is simpler:
{code}
select f(col) as fc, count(*) from table_name group by f(col)
{code}
Contact Tim Ellis (tellis) at RiotGames dot com if you would like to discuss this in further detail.
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