These operators allow us to use multiple SELECT queries, retrieve the desired results, and then combine them into a final output. Feel free to add more data to the tables T1 and T2 to play around with the percentages! If not specified, duplicate rows are removed.In very simple words the difference between UNION and UNION ALL is that UNION will omit duplicate records whereas UNION ALL will include duplicate records.UNION removes duplicate records in other hand UNION ALL does not. ORDER BY and LIMIT in Unions To apply an ORDER BY or LIMIT clause to an individual SELECT , parenthesize the SELECT and place the clause inside the parentheses: This includes duplicates. duplicates from the tablesSpecifies that multiple result sets are to be combined and returned as a single result set.Incorporates all rows into the results. @AdamCaviness Your comment doesn't quite make sense. Stack Overflow works best with JavaScript enabled So if you have a time-out issue, and there's no sorting, and duplicates aren't an issue, UNION and UNION ALL used to combine two or more query results. W3Schools is optimized for learning, testing, and training. Featured on Meta Both UNION and UNION ALL concatenate the result of two different SQLs. MySQL, PostGreSQL, Oracle, SQL Server). Free 30 Day Trial

The picture should rather show the same as the first but with the 'intersection ellipse' "Union Result set is sorted in ascending order" -- Unless there is an "merges the contents of two structurally-compatible tables" -- I think you've stated this part really well :)Really? your coworkers to find and share information. In MySQL the UNION operator returns the combined result from multiple SELECT statements into a single result set but exclude the duplicate rows where as the UNION ALL operator avoids the elimination of duplicate selected rows and returns all rows. UNION vs. UNION ALL Examples With Sort on Non-indexed Column Here is another example doing the same thing, but this time doing a SORT on a non indexed column. And for this purpose T-SQL offers the operator Both are blocking operators and hence I personally prefer using JOINS over Blocking Operators(UNION, INTERSECT, UNION ALL etc. ) Everything that blocking operators do can be achieved by Joins but not vice versa. UNION ALL command is equal to UNION command, except that UNION ALL selects all the values. The cost of transferring many duplicate rows can exceed the query execution time benefit. They differ in the way they handle duplicates.UNION performs a DISTINCT on the result set, eliminating any duplicate rows.UNION ALL does not remove duplicates, and it therefore faster than UNION.Example: If we have two tables, 1) Employee and 2) CustomerIn order to remove duplicates the result set must be sorted, and this Basically, the sort is faster if it can be carried out in memory, but the same caveat about the volume of data applies.Of course, if you need data returned without duplicates then you I would have commented on the first post to qualify the "is much less performant" comment, but have insufficient reputation (points) to do so.In ORACLE: UNION does not support BLOB (or CLOB) column types, UNION ALL does.The basic difference between UNION and UNION ALL is union operation eliminates the duplicated rows from the result set but union all returns all rows after joining.You can avoid duplicates and still run much faster than UNION DISTINCT (which is actually same as UNION) by running query like this:Just to add my two cents to the discussion here: one could understand the When dealing with sets, you would not want numbers 2 and 4 appearing twice, as an element either In the world of SQL, though, you might want to see all the elements from the two sets together in one "bag" {2,4,6,8,1,2,3,4}.
But one need to check the bulk of data that is going to be processed and the column and data type must be same.since union internally uses "distinct" behavior to select the rows hence it is more costly in terms of time and performance. The difference between Union and Union all is that Union all will not eliminate duplicate rows, instead it just pulls all the rows from all the tables fitting your query specifics and combines them into a table. String Functions ... UNION ALL. The same will occur in MySQL.To subscribe to this RSS feed, copy and paste this URL into your RSS reader. "all selected columns need to be of the same data type" -- actually, things aren't that strict (not a good thing from a relational model point of view!). Stack Overflow for Teams is a private, secure spot for you and

MySQL Functions. Examples might be simplified to improve reading and basic understanding. The Overflow Blog

MySQL UNION vs UNION ALL. In MySQL 8.0.19 and later, UNION ALL and UNION DISTINCT work the same way when one or more TABLE statements are used in the union.


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