Important Note to be considered while applying “UNION” and “UNION ALL” Since we have used “Union ALL” the result is from both the tables including duplicates If you check the output, in 1st and eighth-row, retrieved column values are identical. SELECT AuthorName,Age,Skillsets,NumberOfPosts from Authors2021 This is similar to UNION but includes duplicate records and hence repetition of records are seenĮxample 4 : SELECT AuthorName,Age,Skillsets,NumberOfPosts from Authors Usage: Whenever we need to show the cumulative output by avoiding duplicates, we can go for UNION. If we check the output, we do not have duplicate records. i.e the result set produced by 1st query is combined with the result set produced by the 2nd query. So the resultant of Union will be the combination of all records in both the tables. While Union is applied, if there are common records in both the tables, it will take the data from one table and thus avoid duplication. If you look at the output, the data from both the tables are combined and hence we can see the above output. Union of two table result sets, here the common record is displayed only once thus avoiding duplicates Let there be another table named “Authors2021” and have few records as follows: Whenever there is a requirement like combining data across multiple tables or combining data of a single table that evolved from different queries, we can go for UNION. If they differ, we cannot apply “EXCEPT” UNION : Note: EXCEPT can be placed between queries only when the resultant output of both the queries are the same. Usually, “EXCEPT” is used to find out the results of the query that should be identical or not and when the result shows no data means, the query results are identical. Yes, exactly, there is no output as the Left query contains only 1st and 4th rows and the right query contains all rows and when “EXCEPT” is applied, we are seeing only blank data. “EXCEPT” construct is equivalent to the “MINUS” construct in oracle.Įxample 2 : SELECT * from Authors WHERE Skillsets like 'java%'Ĭan you confirm what might be the output for this? Since the “EXCEPT” construct is used, the resultant of the above query will produce second and third records only (that are not available from the 2nd query). The left query produces all 4 records of the table whereas the right query produces only the 1st and 4th records.
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SQL | Join (Inner, Left, Right and Full Joins).SQL | DDL, DQL, DML, DCL and TCL Commands.ISRO CS Syllabus for Scientist/Engineer Exam.ISRO CS Original Papers and Official Keys.GATE CS Original Papers and Official Keys.
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