📅  最后修改于: 2020-11-30 04:52:42             🧑  作者: Mango
本章说明如何更改表的属性,例如更改表名称,更改列名称,添加列以及删除或替换列。
它用于更改Hive中的表。
该语句根据我们希望在表中修改哪些属性而采用以下任何语法。
ALTER TABLE name RENAME TO new_name
ALTER TABLE name ADD COLUMNS (col_spec[, col_spec ...])
ALTER TABLE name DROP [COLUMN] column_name
ALTER TABLE name CHANGE column_name new_name new_type
ALTER TABLE name REPLACE COLUMNS (col_spec[, col_spec ...])
以下查询将表从employee重命名为emp 。
hive> ALTER TABLE employee RENAME TO emp;
重命名表的JDBC程序如下。
import java.sql.SQLException;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.Statement;
import java.sql.DriverManager;
public class HiveAlterRenameTo {
private static String driverName = "org.apache.hadoop.hive.jdbc.HiveDriver";
public static void main(String[] args) throws SQLException {
// Register driver and create driver instance
Class.forName(driverName);
// get connection
Connection con = DriverManager.getConnection("jdbc:hive://localhost:10000/userdb", "", "");
// create statement
Statement stmt = con.createStatement();
// execute statement
stmt.executeQuery("ALTER TABLE employee RENAME TO emp;");
System.out.println("Table Renamed Successfully");
con.close();
}
}
将程序保存在名为HiveAlterRenameTo.java的文件中。使用以下命令来编译和执行该程序。
$ javac HiveAlterRenameTo.java
$ java HiveAlterRenameTo
Table renamed successfully.
下表包含employee表的字段,并显示要更改的字段(粗体)。
Field Name | Convert from Data Type | Change Field Name | Convert to Data Type |
---|---|---|---|
eid | int | eid | int |
name | String | ename | String |
salary | Float | salary | Double |
designation | String | designation | String |
以下查询使用上述数据重命名列名称和列数据类型:
hive> ALTER TABLE employee CHANGE name ename String;
hive> ALTER TABLE employee CHANGE salary salary Double;
下面给出的是JDBC程序来更改列。
import java.sql.SQLException;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.Statement;
import java.sql.DriverManager;
public class HiveAlterChangeColumn {
private static String driverName = "org.apache.hadoop.hive.jdbc.HiveDriver";
public static void main(String[] args) throws SQLException {
// Register driver and create driver instance
Class.forName(driverName);
// get connection
Connection con = DriverManager.getConnection("jdbc:hive://localhost:10000/userdb", "", "");
// create statement
Statement stmt = con.createStatement();
// execute statement
stmt.executeQuery("ALTER TABLE employee CHANGE name ename String;");
stmt.executeQuery("ALTER TABLE employee CHANGE salary salary Double;");
System.out.println("Change column successful.");
con.close();
}
}
将程序保存在名为HiveAlterChangeColumn.java的文件中。使用以下命令来编译和执行该程序。
$ javac HiveAlterChangeColumn.java
$ java HiveAlterChangeColumn
Change column successful.
以下查询将一个名为dept的列添加到employee表。
hive> ALTER TABLE employee ADD COLUMNS (
dept STRING COMMENT 'Department name');
下面给出了将列添加到表的JDBC程序。
import java.sql.SQLException;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.Statement;
import java.sql.DriverManager;
public class HiveAlterAddColumn {
private static String driverName = "org.apache.hadoop.hive.jdbc.HiveDriver";
public static void main(String[] args) throws SQLException {
// Register driver and create driver instance
Class.forName(driverName);
// get connection
Connection con = DriverManager.getConnection("jdbc:hive://localhost:10000/userdb", "", "");
// create statement
Statement stmt = con.createStatement();
// execute statement
stmt.executeQuery("ALTER TABLE employee ADD COLUMNS " + " (dept STRING COMMENT 'Department name');");
System.out.prinln("Add column successful.");
con.close();
}
}
将程序保存在名为HiveAlterAddColumn.java的文件中。使用以下命令来编译和执行该程序。
$ javac HiveAlterAddColumn.java
$ java HiveAlterAddColumn
Add column successful.
以下查询从employee表中删除所有列,并将其替换为emp和name列:
hive> ALTER TABLE employee REPLACE COLUMNS (
eid INT empid Int,
ename STRING name String);
下面给出的是JDBC程序,用于将eid列替换为empid并将ename列替换为name 。
import java.sql.SQLException;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.Statement;
import java.sql.DriverManager;
public class HiveAlterReplaceColumn {
private static String driverName = "org.apache.hadoop.hive.jdbc.HiveDriver";
public static void main(String[] args) throws SQLException {
// Register driver and create driver instance
Class.forName(driverName);
// get connection
Connection con = DriverManager.getConnection("jdbc:hive://localhost:10000/userdb", "", "");
// create statement
Statement stmt = con.createStatement();
// execute statement
stmt.executeQuery("ALTER TABLE employee REPLACE COLUMNS "
+" (eid INT empid Int,"
+" ename STRING name String);");
System.out.println(" Replace column successful");
con.close();
}
}
将程序保存在名为HiveAlterReplaceColumn.java的文件中。使用以下命令来编译和执行该程序。
$ javac HiveAlterReplaceColumn.java
$ java HiveAlterReplaceColumn
Replace column successful.