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content/en/engines/mergetree-table-engine-family/aggregatingmergetree.md

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 ## Merge two data streams
 
 Q.  I have 2 Kafka topics from which I am storing events into 2 different tables (A and B) having the same unique ID. I want to create a single table that combines the data in tables A and B into one table C. The problem is that data received asynchronously and not all the data is available when a row arrives in Table A or vice-versa.
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 A. You can use AggregatingMergeTree with Nullable columns and any aggregation function or Non-Nullable column and max aggregation function if it aceptable for your data. 
 
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