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From Apache Wiki <wikidi...@apache.org>
Subject [Hadoop Wiki] Update of "Hive/LanguageManual/UDF" by AdamKramer
Date Mon, 08 Mar 2010 05:48:17 GMT
Dear Wiki user,

You have subscribed to a wiki page or wiki category on "Hadoop Wiki" for change notification.

The "Hive/LanguageManual/UDF" page has been changed by AdamKramer.
The comment on this change is: Adds a caveat that has been messing me up; also corrects two
typoes..
http://wiki.apache.org/hadoop/Hive/LanguageManual/UDF?action=diff&rev1=34&rev2=35

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

  <<TableOfContents>>
  
  NOTE: These commands will be able to show you the latest function documentations.
+ 
  {{{
  SHOW FUNCTIONS;
  DESCRIBE FUNCTION <function_name>;
  }}}
- 
  == 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.
  ||<10%>'''Operator''' ||<10%>'''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 ||None! ||Fails because of invalid syntax. SQL uses =, not == ||
  ||A <> B ||All primitive types ||TRUE if expression A is NOT equal to expression B
otherwise FALSE ||
  ||A < B ||All primitive types ||TRUE if expression A is less than expression B otherwise
FALSE ||
  ||A <= B ||All primitive types ||TRUE if expression A is less than or equal to expression
B otherwise FALSE ||
@@ -60, +60 @@

  
  === Operators on Complex Types ===
  The following operators provide mechanisms to access elements in  Complex Types
- ||<10%> '''Operator''' ||<10%> '''Operand types''' || '''Description''' ||
+ ||<10%>'''Operator''' ||<10%>'''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. ||
@@ -71, +71 @@

  == Built-in Functions ==
  === Mathematical Functions ===
  The following built-in mathematical functions are supported in hive:
- ||<10%> '''Return Type''' ||<15%> '''Name(Signature)''' || '''Description'''
||
+ ||<10%>'''Return Type''' ||<15%>'''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 ||
@@ -101, +101 @@

  
  === Collection Functions ===
  The following built-in collection functions are supported in hive:
- ||<10%> '''Return Type''' ||<15%> '''Name(Signature)''' || '''Description'''
||
+ ||<10%>'''Return Type''' ||<15%>'''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 ||
  
@@ -110, +110 @@

  
  === Type Conversion Functions ===
  The following type conversion functions are supported in hive:
- ||<10%> '''Return Type''' ||<15%> '''Name(Signature)''' || '''Description'''
||
+ ||<10%>'''Return Type''' ||<15%>'''Name(Signature)''' ||'''Description''' ||
- || <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. ||
+ ||'''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. ||
  
  
  
@@ -146, +146 @@

  
  === String Functions ===
  The following are built-in String functions are supported in hive:
- ||<10%> '''Return Type''' ||<15%> '''Name(Signature)''' || '''Description'''
||
+ ||<10%>'''Return Type''' ||<15%>'''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. ||
@@ -157, +157 @@

  ||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' ||
- ||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' ||
+ ||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) ||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 particular key in QUERY can be extracted using
the syntax QUERY:<KEY_NAME> e.g. QUERY:k1. ||
  ||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 ||
@@ -167, +167 @@

  ||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 ||
  ||list ||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 comman-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 ||
+ ||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 ||
+ 
+ 
  
  
  === Misc. Functions ===
- 
  ==== get_json_object ====
  A limited version of JSONPath is supported:
  
@@ -217, +218 @@

  hive> SELECT get_json_object(src_json.json, '$.non_exist_key') FROM src_json;
  NULL
  }}}
- 
  == Built-in Aggregate Functions (UDAF) ==
  The following are built-in aggregate functions are supported in Hive:
- ||<10%> '''Return Type''' ||<10%> '''Name(Signature)''' || '''Description'''
||
+ ||<10%>Return Type''' ''' ||<10%>Name(Signature)''' ''' ||Description''' '''
||
  ||BIGINT ||count(1), count(DISTINCT col [, col]...) ||count(1) returns the number of members
in the group, whereas the count(DISTINCT col) gets the count of distinct values of the columns
in the group ||
- ||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 ||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 n the group ||
  
+ 
+ 
+ 
  == 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. Currently, the only table-generating function is explode(), which 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.
+ <<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. Currently, the only table-generating function
is explode(), which 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 ||
+ ||Array<int> myCol ||
- || [1,2,3] ||
+ ||[1,2,3] ||
- || [4,5,6] ||
+ ||[4,5,6] ||
+ 
+ 
+ 
  
  Then running the query:
  
  SELECT explode(myCol) AS myNewCol FROM myTable;
  
  Will produce:
- 
- || int myNewCol ||
+ ||int myNewCol ||
- || 1 ||
+ ||1 ||
- || 2 ||
+ ||2 ||
- || 3 ||
+ ||3 ||
- || 4 ||
+ ||4 ||
- || 5 ||
+ ||5 ||
- || 6 ||
+ ||6 ||
+ 
+ 
+ 
  
  Using the syntax "SELECT udtf(col) AS colAlias..." has a few limitations:
  
-   * No other expressions are allowed in SELECT 
+  * No other expressions are allowed in SELECT
-     * SELECT pageid, explode(adid_list) AS myCol... is not supported
+   * SELECT pageid, explode(adid_list) AS myCol... is not supported
-   * UDTF's can't be nested
+  * UDTF's can't be nested
-     * SELECT explode(explode(adid_list)) AS myCol... is not supported
+   * SELECT explode(explode(adid_list)) AS myCol... is not supported
-   * GROUP BY / CLUSTER BY / DISTRIBUTE BY / SORT BY 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
+   * SELECT explode(adid_list) AS myCol ... GROUP BY myCol is not supported
  
  Please see [wiki:Self: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:
- ||<10%> '''Return Type''' ||<10%> '''Name(Signature)''' || '''Description'''
||
+ ||<10%>Return Type''' ''' ||<10%>Name(Signature)''' ''' ||Description''' '''
||
- || <type> || explode(array<type> a) <<Anchor(explode)>> || For each
element in a, explode() generates a row containing that element ||
+ ||'''Expected "=" to follow "type"''' ||explode(array<type> a) <<Anchor(explode)>>
||For each element in a, explode() generates a row containing that element ||
  
+ 
+ 

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