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POHow to incrementally update a table
 

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  1. POHow to incrementally update a table
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    <p>We're using Hive and have a data flow that looks like:</p> <pre><code> SOURCE -&gt; Flume -&gt; S3 Buckets -&gt; Script -&gt; Hive Table </code></pre> <p>We have a table that looks something like, truncated for brevity:</p> <pre><code> CREATE TABLE core_table ( unique_id string update bigint other_data string ) </code></pre> <p>Now we also have the update table - same structure <code>core_update</code> this table may contain duplicated data (e.g. duplicated unique_id, but increasing bigint, also it's ordered later int the file).</p> <p>Is there a good way to apply the updated that are in <code>core_update</code> to <code>core_table</code> while both adding new unique_id's to the table and updating the base data.</p> <p>-- Note: I am trying to avoid something that looks like: MERGE -> DEDUP since that process takes about 3 hours on the smaller datasets, and we've got one dataset that is whomping huge. So doing something that's akin to an insertion sort would be great.</p> <p>Update: Found the following blog post by IBM <a href="http://ibm.co/15bMSxk" rel="nofollow">http://ibm.co/15bMSxk</a> And it says:</p> <p>Algorithm-2: Update into un-partitioned table</p> <ul> <li><p>Step-1 Run the merge join query Input : mainTable, staging table name to hold merged records(call as stagingTable3), un-partitioned staging table name(call as stagingTable2), table primary key, table fields Build the merge join query:</p> <p>insert overwrite table stagingTable3 select each column in "List tableFields" Add field name with the alias A from mainTable with alias A Apply the left outer join with stagingTable2 with alias B Check for where A.primaryKey = B.primaryKey and where B.primaryKey is null</p> <p>Then union with the data selected from stagingTable2</p></li> <li><p>Step-2: Load the data by overwriting from stagingTable3 to mainTable by using the below given load query:</p> <pre><code>load data inpath stagingTable3 overwrite into mainTable </code></pre></li> </ul> <p>However this still doesn't quite make sense (or work in my interpretation).</p>
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