如何在sql查询中传递java字符串变量。我已完成所有JDBC连接。
我的sql数据库查询是
sql = "Select *
from production AS cust
INNER JOIN location AS comp
ON cust.location_id = comp.location_id
where comp.name = locationnames AND crop_id =1";
它不起作用。但是，如果我执行以下代码，它的工作
sql = "Select *
from production AS cust
INNER JOIN location AS comp
ON cust.location_id = comp.location_id
where comp.name = "\taplejung"\
AND crop_id =1";
现在告诉我如何将变量名传递给sql查询来执行此操作。 Jst告诉我如何将变量locationnames传递给comp.name。
我的完整java函数如下所示：locationCombo表示在组合框中选择的项目。 CropCombo也表示相同......
public void displayYearwise() throws SQLException, ClassNotFoundException{
//jComboBox4.setSelectedItem("Crops");
//DefaultCategoryDataset dataset = new DefaultCategoryDataset();
XYSeriesCollection dataset = new XYSeriesCollection();
XYSeries series = new XYSeries("production");
XYSeries series1 = new XYSeries("scat");
String JDBC_DRIVER="com.mysql.jdbc.Driver";
String DB_URL="jdbc:mysql://localhost/data2";
Connection conn;
Statement stmt;
String USER = "root";
String PASS = "";
Object cropname = CropCombo.getSelectedItem();
String cropnames = cropname.toString();
Object locationname = locationCombo.getSelectedItem();
// String locationnames = locationname.toString();
String locationnames = "taplejung";
String pd="paddy ";
System.out.println(cropnames.length()+" "+pd.length());
System.out.println(cropsList);
String sql=null;
if(cropnames.equals("paddy"))
{
//System.out.println();
sql="Select *
from production AS cust
INNER JOIN location AS comp
ON cust.location_id = comp.location_id
WHERE comp.name = "+locationnames+"
AND crop_id =1";
}
else{
sql="SELECT *
FROM `production`
WHERE crop_id = 4
AND location_id = 10";
}
try{
Class.forName(JDBC_DRIVER);
conn=DriverManager.getConnection(DB_URL,USER,PASS);
System.out.println("Creating statement...");
stmt = conn.createStatement();
System.out.println(sql);
ResultSet rs=stmt.executeQuery(sql);
while (rs.next()){
//String student = rs.getString("studentname");
String yeartext = rs.getString("year_of_production");
//double value = Double.parseDouble(text);
String productiontext = rs.getString("production_amount");
Double yield = rs.getDouble("yield_amount");
double production = Double.parseDouble(productiontext);
double year = Double.parseDouble(yeartext);
series.add(year,production) ;
series1.add(year,yield) ;
//dataset.addSeries(series);
}
dataset.addSeries(series);
dataset.addSeries(series1);
chartArea.removeAll();
JFreeChart chart = ChartFactory.createScatterPlot("Scatter Plot","Year","Paddy Production", dataset);
// JFreeChart chart = ChartFactory.createScatterPlot("Scatter Plot","Year","Paddy Production", dataset, PlotOrientation.HORIZONTAL, rootPaneCheckingEnabled, rootPaneCheckingEnabled, rootPaneCheckingEnabled);
// CategoryPlot p = chart.getCategoryPlot();
//XYPlot xyplot = (XYPlot)jfreechart.getPlot();
//http://stackoverflow.com/questions/12417732/jfreechart-with-scroller
ChartPanel chartPanel = new ChartPanel(chart, false);
chartArea.setLayout(new BorderLayout());
chartArea.add(chartPanel, BorderLayout.EAST);
chartArea.add(chartPanel);
SwingUtilities.updateComponentTreeUI(this);
// p.setRangeGridlinePaint(blue);
chartArea.updateUI();
System.out.println("Database created successfully...");
}
catch(SQLException se)
{
//Handle errors for JDBC
System.out.println("Connect failed ! ");
se.printStackTrace();
// JOptionPane.showMessageDialog(MajorUI.this, err.getMessage());
}
}
答案 0 :(得分：5)
String locationnames = "taplejung";
String sql = "Select * from production AS cust INNER JOIN location AS comp ON cust.location_id = comp.location_id where comp.name ='"+ locationnames +"' AND crop_id =1";
答案 1 :(得分：5)
使用PreparedStatement并绑定String参数
final String sql = "select * from production AS cust INNER JOIN location"
+ " AS comp ON cust.location_id = comp.location_id where "
+ "comp.name = ? AND crop_id = 1";
PreparedStatement ps = null;
try {
ps = conn.prepareStatement(sql);
ps.setString(1, "taplejung");
} catch (Exception e) {
e.printStackTrace();
} finally {
if (ps != null) {
try {
ps.close();
} catch (Exception ignored) {
}
}
}
修改（根据您的其他代码，将其更改为类似的内容）
PreparedStatement ps = null;
String sql = null;
if (cropnames.equals("paddy")) {
// System.out.println();
sql = "SELECT * FROM `production` AS cust INNER JOIN location AS comp "
+ "ON cust.location_id = comp.location_id WHERE comp.name = "
+ "? AND crop_id = 1";
} else {
sql = "SELECT * FROM `production` WHERE crop_id = 4 AND location_id = 10";
}
ps = conn.prepareStatement(sql);
if (cropnames.equals("paddy")) {
ps.setString(1, locationnames);
}
System.out.println(sql);
ResultSet rs = ps.executeQuery();
答案 2 :(得分：0)
每当我必须进行sql查询时，我都会使用像jdbi这样的库来完成它。这将允许您创建具有不同查询的界面。您所要做的就是定义接口，创建POJO，并在SQL表和Java POJO之间创建映射器。
界面看起来像这样。
@RegisterMapper(ProductionMapper.class)
public interface ProductionDAO {
@SqlQuery("Select * from production AS cust INNER JOIN location AS comp ON cust.location_id = comp.location_id where comp.name = :name AND crop_id =1")
Production findRow(@Bind("name") String name);
}
POJO看起来像这样。
public class Production {
private VariableTypeA variableA;
// other variables
public Production(VariableTypeA variableA ....) {
this.variableA = variableA;
// set everything else
}
// getters and setters
}
映射器看起来像这样。
public class ProductionMapper implements ResultSetMapper<Production> {
public Production map(int index, ResultSet r, StatementContext ctx) throws SQLException {
return new Production(r.getSomeType("columnName"), ...);
}
}
这种设计使得与数据库交互并传递变量以及使您的类不违反SRP非常简单
答案 3 :(得分：0)
使用java在mysql查询中传递变量很简单。
非常感谢你有一个美好的一天。
@覆盖 public LinkedList getNameList（String condition，String tableName，String projectName）{ // TODO自动生成的方法存根
String query = "select distinct("+condition+") as name from "+tableName+" ";
//System.out.println(query);
ResultSet rs = null;
PreparedStatement preparedStatement = null;
Connection connection = null;
LinkedList finalList = new LinkedList();
try{
connection = dataSourceAbacus.getConnection();
preparedStatement = connection.prepareStatement(query);
rs= preparedStatement.executeQuery();
while(rs.next()){
finalList.add(rs.getString("name"));
}
}catch(Exception e){
e.printStackTrace();
}finally{
if(connection !=null){
try {
connection.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
if(preparedStatement != null){
try{
preparedStatement.close();
}catch(Exception e){
e.printStackTrace();
}
}
if(rs != null){
try{
rs.close();
}catch(Exception e){
e.printStackTrace();
}
}
}
return finalList;
}