JDBC mysql不支持PreparedStatement中的LIMIT占位符？

Posted 2023-03-27

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【中文标题】JDBC mysql不支持PreparedStatement中的LIMIT占位符？【英文标题】：JDBC mysql does not support placeholder of LIMIT in PreparedStatement? 【发布时间】：2016-01-12 12:51:38 【问题描述】：

我使用mysql-connector-java-5.1.38在Windows 10 64位上操作mysql-community-5.7.10.0。

我尝试在limit 中绑定值以进行分页

"SELECT * FROM employee LIMIT ?, ?"

但是结果显示：

com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '?, ?' at line 1
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
    at java.lang.reflect.Constructor.newInstance(Unknown Source)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:404)
    at com.mysql.jdbc.Util.getInstance(Util.java:387)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:939)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3878)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3814)
    at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2478)
    at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2625)
    at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2547)
    at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2505)
    at com.mysql.jdbc.StatementImpl.executeQuery(StatementImpl.java:1370)
    at SqlTest.main(SqlTest.java:65)

不过，我直接在navicat中试了sql，却能得到正确答案：

INSERT INTO employee VALUES (1, 'Zara');
INSERT INTO employee VALUES (2, 'Zara');
INSERT INTO employee VALUES (3, 'Zara');
INSERT INTO employee VALUES (4, 'Zara');
SET @skip=1; SET @numrows=5;
PREPARE STMT FROM 'SELECT * FROM employee LIMIT ?, ?';
EXECUTE STMT USING @skip, @numrows;

这是我的全部代码：

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

public class SqlTest 
  // JDBC driver name and database URL
  static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";
  static final String DB_URL = "jdbc:mysql://localhost:3306/employee?useServerPrepStmts=false";
  // Database credentials
  static final String USER = "root";
  static final String PASS = "whaty123";

  static final int PAGESIZE = 10;

  public static void main(String[] args) 
    Connection conn = null;
    Statement stmt = null;
    PreparedStatement pStmt = null;

    // STEP 2: Register JDBC driver
    try 
      Class.forName("com.mysql.jdbc.Driver");
     catch (ClassNotFoundException e) 
      e.printStackTrace();
    

    // STEP 3: Open a connection
    System.out.println("Connecting to database...");
    try 
      conn = DriverManager.getConnection(DB_URL, USER, PASS);
     catch (SQLException e) 
      e.printStackTrace();
    

    String insertPreparedSql = "INSERT INTO employee " + "VALUES (?, 'Zara')";

    try 
      pStmt = conn.prepareStatement(insertPreparedSql);
     catch (SQLException e) 
      e.printStackTrace();
    

    for (int i = 0; i < 100; i++) 
      try 
        pStmt.setInt(1, i);
        pStmt.execute();
       catch (SQLException e) 
        e.printStackTrace();
      
    

    String selectLimitSql = "SELECT * FROM employee LIMIT ?, ?";
    // select with limit
    try 
      pStmt = conn.prepareStatement(selectLimitSql);
      pStmt.setFetchSize(PAGESIZE);
      pStmt.setMaxRows(PAGESIZE);
      pStmt.setFetchDirection(ResultSet.FETCH_FORWARD);
      int pageNo = 0;
      pStmt.setInt(1, pageNo * PAGESIZE);
      pStmt.setInt(2, PAGESIZE);
      ResultSet rs = pStmt.executeQuery(selectLimitSql);
      while (!rs.wasNull()) 
        while(rs.next()) 
          System.out.println("id: " + String.valueOf(rs.getInt(1)) + " name: " + rs.getString(2));
        
        pageNo = pageNo + 1;
        pStmt.setInt(1, pageNo * PAGESIZE);
        pStmt.setInt(2, PAGESIZE);
        pStmt.executeQuery(selectLimitSql);
      
      rs.close();
     catch (SQLException e) 
      e.printStackTrace();

【问题讨论】：

在13.2.9 SELECT Syntax 中，它说在准备好的语句中，可以使用 LIMIT 指定参数？占位符标记。 @Abhik Chakraborty 【参考方案1】：

您的问题与 LIMIT 的语法或 MySQL 支持无关，因为它受到支持。问题在于您执行PreparedStatement 的方式。

在使用PreparedStatement 时，您可能不会使用executeQuery(String sql)，因为您之前已经为执行准备了SQL 字符串，无需在executeQuery() 方法中再次传递它。这样做吧

ResultSet rs = pStmt.executeQuery();

而不是

ResultSet rs = pStmt.executeQuery(selectLimitSql);

再次传递selectLimitSql（如上行），您将忽略以下行：

pStmt.setInt(1, pageNo * PAGESIZE);
pStmt.setInt(2, PAGESIZE);

这就像执行包含 '?, ?' 占位符的原始纯 sql，然后您会遇到该异常。

【讨论】：

【参考方案2】：

您不需要传递查询字符串。这样做

 ResultSet rs = pStmt.executeQuery();

而不是

ResultSet rs = pStmt.executeQuery(selectLimitSql);

此外，请删除以下行，因为在查询本身中会处理 limit 的分页。

pStmt.setFetchSize(PAGESIZE);
pStmt.setMaxRows(PAGESIZE);
pStmt.setFetchDirection(ResultSet.FETCH_FORWARD);