[Hadoop Wiki] Update of "Hive/LanguageManual/UDF" by MayankLahiri

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The "Hive/LanguageManual/UDF" page has been changed by MayankLahiri.
The comment on this change is: added entries for UDAFs: variance, stddev, percentile, percentile_approx, histogram_numeric.
http://wiki.apache.org/hadoop/Hive/LanguageManual/UDF?action=diff&rev1=43&rev2=44

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  == Built-in Aggregate Functions (UDAF) ==
  The following are built-in aggregate functions are supported in Hive:
  ||<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 ||
+ ||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 ||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 ||
+ ||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 ||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 ||
  
  == 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.