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inbs
Aged Yak Warrior
860 Posts |
 Posted - 2012-01-05 : 01:42:47
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| i have 2 tables Products:ProductCodeSales:ItemCodeDELETE ProductsWHERE NOT EXISTS(SELECT ProductCode FROM Sales WHERE ItemCode=Products.ProductCode)How is it run, ProductCode is non colum in Sales table? |
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khtan
In (Som, Ni, Yak)
17689 Posts |
Posted - 2012-01-05 : 01:46:08
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[code]ItemCode=Products.ProductCode[/code]It is matching ProductCode from Products table with ItemCode from Sales table
KH[spoiler]Time is always against us[/spoiler] |
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inbs
Aged Yak Warrior
860 Posts |
Posted - 2012-01-05 : 02:02:45
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| i do not understand,ProductCode it is not belonging to sales table.(SELECT ProductCode FROM Sales)--> it isn't TRUE??and the match it come after the SELECT |
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khtan
In (Som, Ni, Yak)
17689 Posts |
Posted - 2012-01-05 : 02:11:55
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| * nothing here, move on * |
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khtan
In (Som, Ni, Yak)
17689 Posts |
Posted - 2012-01-05 : 02:14:57
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[code](SELECT ProductCode FROM SalesWHERE ItemCode=Products.ProductCode)[/code]You are selecting the ProductCode from Products table in this query. It is the same as the ProductCode in the WHERE statement. If you removed the table prefix Products it will still work.But for good programming practice, it is better to prefix all your column.Also for exists, it does not matter the column list in the SELECT does not really matter, a "*" will work. [code](SELECT * FROM SalesWHERE ItemCode=Products.ProductCode)[/code]
KH[spoiler]Time is always against us[/spoiler] |
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inbs
Aged Yak Warrior
860 Posts |
Posted - 2012-01-05 : 02:28:37
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| i understand that the Products.ProductCode it is the same column (ItemCode)what is Operation orders of query (in the back)?is'nt engine look for fist the ProductCode in sales table ? |
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khtan
In (Som, Ni, Yak)
17689 Posts |
Posted - 2012-01-05 : 02:30:43
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if the ProductCode column only exists in one of the table, it will not give error. If not, you will have to prefix with the table name
KH[spoiler]Time is always against us[/spoiler] |
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vijays3
Constraint Violating Yak Guru
354 Posts |
Posted - 2012-01-06 : 01:33:01
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| This is correllated subqueries .To undestand this Please go through thishttp://msdn.microsoft.com/en-us/library/ms187638.aspx |
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strange query