![]() This is also one of the popular SQL Interview Questions so knowing how. You can use any of the approaches to remove duplicates from tables using SQL. That's a spillover from SQL Server - as is your whole approach. In this article, I am going to share 2 ways to remove duplicate rows from SQL, first by using GROUP BY and HAVING clause and second by using the RANK function which works on most of the databases. The target of a DELETE statement cannot be the CTE, only the underlying table. How to use the physical location of rows (ROWID) in a DELETE statement How do I (or can I) SELECT DISTINCT on multiple columns? Its values can change between commands due to background processes or concurrent write operations (but not within the same command). Or use IS NOT DISTINCT FROM to compare values (which may exclude some indexes).Ĭtid is an implementation detail of Postgres, it's not in the SQL standard and can change between major versions without warning (even if that's very unlikely). Else, depending on your definition of "duplicate", you'll need one approach or the other. Does not matter for columns defined NOT NULL. Important difference: These other queries treat NULL values as not equal, while GROUP BY (or DISTINCT or DISTINCT ON ()) treats NULL values as equal. Both should result in the same query plan. So is a self-join with the USING clause like added later. Using EXISTS as demonstrated by is typically faster. ) is a tricky query style when NULL values can be involved, but the system column ctid is never NULL. The above query is short, conveniently listing column names only once. GROUP BY name, address, zipcode) - list columns defining duplicates SELECT min(ctid) - ctid is NOT NULL by definition
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