Comments on: Aggregating in SQL across multiple levels and along several dimensions using ROLLUP and GROUPING SETS https://technology.amis.nl/2006/04/18/aggregating-in-sql-across-multiple-levels-and-along-several-dimensions-using-rollup-and-grouping-sets/ Friends of Oracle and Java Sat, 01 Aug 2015 11:10:05 +0000 hourly 1 http://wordpress.org/?v=4.2.3 By: Viliam https://technology.amis.nl/2006/04/18/aggregating-in-sql-across-multiple-levels-and-along-several-dimensions-using-rollup-and-grouping-sets/#comment-3143 Wed, 19 Apr 2006 07:53:37 +0000 http://technology.amis.nl/blog/?p=1154#comment-3143 A remark to a statement, that UNION (ALL) is “less than perfect performing”:
* UNION is bad performing, it has to sort all queries and remove duplicates
* UNION ALL is perfectly performing, it just executes first query, returns rows, executes the second and returns rows. It is equal to executing both queries.

Viliam

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