Sep 8, 2008 · The cost of UNION ALL is that the SQL engine must first create a temporary unique index for columns used as keys, and then run all subqueries to store their results in that index. Then it will …

You cannot use WITH in the middle of a query expression. WITH is used to build up intermediate queries for use by other queries immediately after (meaning it cannot be used by multiple …

May 25, 2009 · 76 UNION combines the results of two or more queries into a single result set that includes all the rows that belong to all queries in the union. By using JOINs, you can retrieve data …

Mar 10, 2021 · Joins are horizontal, unions are vertical. All queries in a union must have the same number of columns with the same datatypes. However you only need to alias the columns in the first …

Mar 27, 2011 · Basically, the UNION is looking for two complete SELECT statements to combine, and the WHERE clause is part of the SELECT statement. It may make more sense to apply the outer …

Nov 30, 2022 · Use proper column selection, this will prevent issues when columns to one of the tables are added or columns from one of them are removed without your knowledge.

Per the SQL Standard, the order of results is undefined barring an explicit order by clause. That first select in your example probably returns its results in the order returned by the subselect, but it is not …

In SQL Server this inserts 100 records, from the Customers table into tmpFerdeen :- SELECT top(100)* INTO tmpFerdeen FROM Customers Is it possible to do a SELECT INTO across a UNION ALL …

Mar 20, 2017 · I'm doing a UNION of two queries on an Oracle database. Both of them have a WHERE clause. Is there a difference in the performance if I do the WHERE after UNIONing the queries …

Oct 11, 2010 · 18 You would use UNION ALL when you really do need the multiple 'copies' of rows that would otherwise be removed when using UNION. It can also be faster on the query end, since the …