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AskSQLTeam
Ask SQLTeam Question
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 Posted - 2001-06-29 : 09:37:18
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| J Teb writes "How efficient is it to use a UNION subquery in the FROM of a statement. I need to sum together a column that exists in two different tables. For instance a sales record that has data in a current working table tblSalesToday and a history table tblSalesHistory (very large table) both with a NumSales column. As of now I have a similar statement "Select Sum(TSS.NumSales) FROM (Select * FROM tblSalesToday UNION Select * FROM tblSalesHistory)" . This is a simple solution but seems extremely inefficient. Any advice would be helpful. thanks" |
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UNION subquery efficiency