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Drill team is sometimes asked how to find if the table data has inherent skew.
Suppose you want to find out if a particular column ‘a1’ has data skew. You can run the following query:
SELECT a1, COUNT(*) as cnt FROM T1
GROUP BY a1 ORDER BY cnt DESC limit 10;
If there is significant data skew, the top few counts will be much higher than the other count values.
Retrieving data ...