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Written by Asif
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Wednesday, 21 March 2007 |
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GROUP BY… was added to SQL because aggregate functions (like SUM) return the aggregate of all column values every time they are called, and without the GROUP BY function it was impossible to find the sum for each individual group of column values.
The syntax for the GROUP BY function is: SELECT column, SUM (column) FROM table GROUP BY column GROUP BY Example This "Sales" Table: | Company | Amount | | W3Schools | 5500 | | IBM | 4500 | | W3Schools | 7100 | And This SQL: | SELECT Company, SUM(Amount) FROM Sales | Returns this result: | Company | SUM(Amount) | | W3Schools | 17100 | | IBM | 17100 | | W3Schools | 17100 | The above code is invalid because the column returned is not part of an aggregate. A GROUP BY clause will solve this problem: | SELECT Company,SUM(Amount) FROM Sales GROUP BY Company | Returns this result: | Company | SUM(Amount) | | W3Schools | 12600 | | IBM | 4500 | |
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Last Updated ( Monday, 17 September 2007 )
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