JDBC mysql不支持PreparedStatement中的LIMIT占位符？

Question

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();
    }
  }

}

Answer 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。

Answer 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);

以下代码有效：

    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/company?useServerPrepStmts=false";
      // Database credentials
      static final String USER = "root";
      static final String PASS = "rohan";

      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', 'Zara','Zara')";

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

        for (int i = 0; i < 100; i++) {
          try {
            pStmt.setInt(1, i*10);
            pStmt.execute();
          } catch (SQLException e) {
            e.printStackTrace();
          }
        }

        String selectLimitSql = "SELECT * FROM employee limit ?, ?";
        // select with limit
        try {
          pStmt = conn.prepareStatement(selectLimitSql);
          int pageNo = 0;
          pStmt.setInt(1, pageNo * PAGESIZE);
          pStmt.setInt(2, PAGESIZE);
          ResultSet rs = pStmt.executeQuery();
          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);
            rs = pStmt.executeQuery();
          }
          rs.close();
        } catch (SQLException e) {
          e.printStackTrace();
        }
      }

    }