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From Apache Wiki <wikidi...@apache.org>
Subject [Hadoop Wiki] Update of "Hive/Tutorial" by Ning Zhang
Date Fri, 16 Apr 2010 19:15:17 GMT
Dear Wiki user,

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The "Hive/Tutorial" page has been changed by Ning Zhang.


    * An additional pvs.country column is added in the select statement. This is the corresponding
input column for the dynamic partition column. Note that you do not need to add an input column
for the static partition column because its value is already known in the PARTITION clause.

  Semantics of the dynamic partition insert statement:
+   * When there are already non-empty partitions exists for the dynamic partition columns,
(e.g., country='CA' exists under some ds root partition), it will be overwritten if the dynamic
partition insert saw the same value (say 'CA') in the input data. This is in line with the
'insert overwrite' semantics. However, if the partition value 'CA' does not appear in the
input data, the existing partition will not be overwritten. 
    * Since a Hive partition corresponds to a directory in HDFS, the partition value has to
conform to the HDFS path format (URI in Java). Any character having a special meaning in URI
(e.g., '%', ':', '/', '#') will be escaped with '%' followed by 2 bytes of its ASCII value.
    * If the input column is a type different than STRING, its value will be first converted
to STRING to be used to construct the HDFS path. 
    * If the input column value is NULL or empty string, the row will be put into a special
partition, whose name is controlled by the hive parameter hive.exec.default.dynamic.partition.name.
The default value is __HIVE_DEFAULT_PARTITION__. Basically this partition will contain all
"bad" rows whose value are not valid partition names. The caveat of this approach is that
the bad value will be lost and is replaced by __HIVE_DEFAULT_PARTITION__ if you select them
Hive. JIRA HIVE-1309 is a solution to let user specify "bad file" to retain the input partition
column values as well.

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