译注：书接上篇，了解过创建表以及load data后，假如发现需要更改表字段类型或者添加表字段，怎么办？这篇文章将进一步了解具体细节。
This chapter explains how to alter the attributes of a table such as changing its table name, changing column names, adding columns, and deleting or replacing columns.
Alter Table Statement
It is used to alter a table in Hive.
Syntax
The statement takes any of the following syntaxes based on what attributes we wish to modify in a table.
ALTER TABLE name RENAME TO new_name ALTER TABLE name ADD COLUMNS (col_spec[, col_spec ...]) ALTER TABLE name DROP [COLUMN] column_name ------------ 译注：这个drop命令，我在工作中，并没有生效，而是利用表级别的REPLACE进行替换式删除字段的 ALTER TABLE name CHANGE column_name new_name new_type ALTER TABLE name REPLACE COLUMNS (col_spec[, col_spec ...])
Rename To… Statement
The following query renames the table from employee to emp.
hive> ALTER TABLE employee RENAME TO emp;
JDBC Program
The JDBC program to rename a table is as follows.
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();
}
}
Save the program in a file named HiveAlterRenameTo.java. Use the following commands to compile and execute this program.
$ javac HiveAlterRenameTo.java $ java HiveAlterRenameTo
Output:
Table renamed successfully.
Change Statement
The following table contains the fields of employee table and it shows the fields to be changed (in bold).
| 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 |
The following queries rename the column name and column data type using the above data:
hive> ALTER TABLE employee CHANGE name ename String; hive> ALTER TABLE employee CHANGE salary salary Double;
JDBC Program
Given below is the JDBC program to change a column.
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();
}
}
Save the program in a file named HiveAlterChangeColumn.java. Use the following commands to compile and execute this program.
$ javac HiveAlterChangeColumn.java $ java HiveAlterChangeColumn
Output:
Change column successful.
Add Columns Statement
The following query adds a column named dept to the employee table.
hive> ALTER TABLE employee ADD COLUMNS (dept STRING COMMENT ‘Department name‘);
-- 有一些文章里说 add columns dept STRING COMMENT ‘comment‘ ;但是在一些高版本里，需要把你需要加的列放到括号里（）
JDBC Program
The JDBC program to add a column to a table is given below.
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();
}
}
Save the program in a file named HiveAlterAddColumn.java. Use the following commands to compile and execute this program.
$ javac HiveAlterAddColumn.java $ java HiveAlterAddColumn
Output:
Add column successful.
Replace Statement
The following query deletes all the columns from the employee table and replaces it with emp and name columns:
hive> ALTER TABLE employee REPLACE COLUMNS ( eid INT empid Int, ename STRING name String);
JDBC Program
Given below is the JDBC program to replace eid column with empid and ename column with 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();
}
}
Save the program in a file named HiveAlterReplaceColumn.java. Use the following commands to compile and execute this program.
$ javac HiveAlterReplaceColumn.java $ java HiveAlterReplaceColumn
Output:
Replace column successful. Drop Table主要就一个命令，就不单独再搞一篇了，在此一并搞了。--------------------------------------------------
Drop Table Statement
The syntax is as follows:
DROP TABLE [IF EXISTS] table_name;
The following query drops a table named employee:
hive> DROP TABLE IF EXISTS employee;
On successful execution of the query, you get to see the following response:
OK Time taken: 5.3 seconds hive>
--------------------------------------------------- 译注：本章中一些操作，我个人并没有一一验证。后续使用到并验证后，如果有问题，会备注进去。目前里面的内容基本都是英文文章里的内容。 ------------英文地址：https://www.tutorialspoint.com/hive/hive_alter_table.htm