[英]How to check database for duplicates before inserting?
我想在插入數據庫之前檢查數據庫是否重復。 僅當plateNo,driverID和resDate匹配時才被視為重復項。
這是我獲取將要插入數據庫的數據的方式
private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {
String client = (String) clientCmb.getSelectedItem();
String[] cparts = client.split("-");
String cpart = cparts[0];
String driver = (String) driverCmb.getSelectedItem();
String[] dparts = driver.split("-");
String dpart = dparts[0];
String van = (String) vanCmb.getSelectedItem();
java.util.Date oDate = jXDatePicker2.getDate();
DateFormat oDateFormat = new SimpleDateFormat("yyyy-MM-dd");
String date = oDateFormat.format(oDate);
model2.addRow(cpart, dpart, van, date);
}
這是我的addRow方法的代碼
public void addRow(String client, String driver, String van, String res){
try {
String sqlRes = "Select * from reservation";
rs = st.executeQuery(sqlRes);
rs.moveToInsertRow();
rs.updateString("clientID", client);
rs.updateString("plateNo", van);
rs.updateString("driverID", driver);
rs.updateString("resDate", res);
rs.insertRow();
rs.moveToCurrentRow();
rs = st.executeQuery(sqlRes);
this.fireTableDataChanged();
} catch (SQLException ex) {
Logger.getLogger(MyModel2.class.getName()).log(Level.SEVERE, null, ex);
}
讓數據庫為您完成工作。 定義一個唯一的索引/約束,指定這三個值在表中是唯一的:
create unique index unq_reservation_3 on reservation(plateNo, driverID, resDate);
如果您嘗試插入重復項-或執行導致重復項的update
-數據庫將返回錯誤。 您只需要捕獲錯誤。
使用MERGE
語句: T-SQL或ORACLE ,或者對於MySQL:
PreparedStatement p = con.prepareStatement("
INSERT INTO reservation tgt (clientID, plateNo, driverID, resDate)
SELECT (? As clientID, ? As plateNo, ? As driverID, ? As resDate)
FROM DUAL ins
LEFT JOIN reservation ref
ON ref.resDate = ins.resDate
AND (ref.plateNo = ins.plateNo OR ref.driverID = ins.driverID)
WHERE ref.clientID IS NULL;
");
p.setString(1, client);
p.setString(2, van);
p.setString(3, driver);
p.setString(4, res);
return p.executeUpdate(); /* 1 - Success | 0 - Ignored Duplicate */
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