java查询数据库表

① 如何在java 中的PreparedStatement 语句中来判断一个数据库表是否存在

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

import util.DBUtil;

public class TableExistTest {
public static void main(String[] args) {
String tableName = "test1";
Connection con = null;
ResultSet rs = null;
PreparedStatement ps = null;
String sql = "SELECT NAME FROM sysobjects WHERE NAME='" + tableName
+ "'";
System.out.println(sql);
try {
con = DBUtil.getConnection();//取得数据库连接
ps = con.prepareStatement(sql);
rs = ps.executeQuery();
if (rs.next()) {
System.out.println("存在" + tableName);
} else {
System.out.println("不存在" + tableName);
}
} catch (SQLException e) {
e.printStackTrace();
} finally {
try {
if (rs != null)
rs.close();
if (ps != null)
ps.close();
if (con != null)
con.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}

}

附加提示：

你在查询分析器里面执行这条语句，你会很兴奋

SELECT * FROM sysobjects

② java如何获得数据库表中各字段的字段名

Java获取数据库的表中各字段的字段名，代码如下：
import java.sql.Connection;import java.sql.DriverManager;import java.sql.ResultSet;import java.sql.PreparedStatement;import java.sql.ResultSetMetaData;import java.sql.SQLException;public class TestDemo {public static Connection getConnection() {Connection conn = null;try {Class.forName("com.mysql.jdbc.Driver");String url = "jdbc:mysql://数据库IP地址:3306/数据库名称";String user = "数据库用户名";String pass = "数据库用户密码";conn = DriverManager.getConnection(url, user, pass);} catch (ClassNotFoundException e) {e.printStackTrace();} catch (SQLException e) {e.printStackTrace();}return conn;}public static void main(String[] args) {Connection conn = getConnection();String sql = "select * from AccessType";PreparedStatement stmt;try {stmt = conn.prepareStatement(sql);ResultSet rs = stmt.executeQuery(sql);ResultSetMetaData data = rs.getMetaData();for (int i = 1; i <= data.getColumnCount(); i++) {// 获得所有列的数目及实际列数int columnCount = data.getColumnCount();// 获得指定列的列名String columnName = data.getColumnName(i);// 获得指定列的列值int columnType = data.getColumnType(i);// 获得指定列的数据类型名String columnTypeName = data.getColumnTypeName(i);// 所在的Catalog名字String catalogName = data.getCatalogName(i);// 对应数据类型的类String columnClassName = data.getColumnClassName(i);// 在数据库中类型的最大字符个数int columnDisplaySize = data.getColumnDisplaySize(i);// 默认的列的标题String columnLabel = data.getColumnLabel(i);// 获得列的模式String schemaName = data.getSchemaName(i);// 某列类型的精确度(类型的长度)int precision = data.getPrecision(i);// 小数点后的位数int scale = data.getScale(i);// 获取某列对应的表名String tableName = data.getTableName(i);// 是否自动递增boolean isAutoInctement = data.isAutoIncrement(i);// 在数据库中是否为货币型boolean isCurrency = data.isCurrency(i);// 是否为空int isNullable = data.isNullable(i);// 是否为只读boolean isReadOnly = data.isReadOnly(i);// 能否出现在where中boolean isSearchable = data.isSearchable(i);System.out.println(columnCount);System.out.println("获得列" + i + "的字段名称:" + columnName);System.out.println("获得列" + i + "的类型,返回SqlType中的编号:"+ columnType);System.out.println("获得列" + i + "的数据类型名:" + columnTypeName);System.out.println("获得列" + i + "所在的Catalog名字:"+ catalogName);System.out.println("获得列" + i + "对应数据类型的类:"+ columnClassName);System.out.println("获得列" + i + "在数据库中类型的最大字符个数:"+ columnDisplaySize);System.out.println("获得列" + i + "的默认的列的标题:" + columnLabel);System.out.println("获得列" + i + "的模式:" + schemaName);System.out.println("获得列" + i + "类型的精确度(类型的长度):" + precision);System.out.println("获得列" + i + "小数点后的位数:" + scale);System.out.println("获得列" + i + "对应的表名:" + tableName);System.out.println("获得列" + i + "是否自动递增:" + isAutoInctement);System.out.println("获得列" + i + "在数据库中是否为货币型:" + isCurrency);System.out.println("获得列" + i + "是否为空:" + isNullable);System.out.println("获得列" + i + "是否为只读:" + isReadOnly);System.out.println("获得列" + i + "能否出现在where中:"+ isSearchable);}} catch (SQLException e) {e.printStackTrace();}}}