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[英]Delphi FireDac subsequent parameterized MySQL StoredProcedure execution fails with "Lost connection to MySQL server during query" exception
[英]Delphi, FireDAC, MySQL Query
qClient.SQL.Clear;
qClient.SQL.Text := 'Select C.Lastname,C.Firstname,C.Clino,C.Address,' +
'C.City,C.State,C.Zip,C.Phone,C.HerCell,C.HisCell,' +
'C.Texting,C.Since,C.Selected,' +
'SUM( I.Charges - I.Discount ) as Revenue ' +
'from Client C join Invoice I ' +
'on I.Clino = C.Clino ' +
'where I.Date between :S and :E ' +
'and I.Inv = true ' +
'group by C.Clino ' +
'order by Revenue desc ';
qClient.ParamByName('S').AsDate := dStart;
qClient.ParamByName('E').AsDate := dEnd;
qClient.DetailFields := 'Clino';
qClient.Open();
如何修改上面的代碼,以便查詢僅包含超過最小值(例如可能為 1000)的“收入”值? 它目前包括所有客戶端。
謝謝,斯派克
你需要一個HAVING
子句:
qClient.SQL.Text := 'Select C.Lastname,C.Firstname,C.Clino,C.Address,' +
'C.City,C.State,C.Zip,C.Phone,C.HerCell,C.HisCell,' +
'C.Texting,C.Since,C.Selected,' +
'SUM( I.Charges - I.Discount ) as Revenue ' +
'from Client C join Invoice I ' +
'on I.Clino = C.Clino ' +
'where I.Date between :S and :E ' +
'and I.Inv = true ' +
'group by C.Clino ' +
'having Revenue > 1000 ' +
'order by Revenue desc ';
HAVING
子句應用條件並過濾聚合后的查詢結果。
在這種情況下Revenue
是聚集的柱,不能一個中使用WHERE
子句,其還過濾的查詢,因為條件WHERE
聚集之前被施加子句。
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