Hive 简明教程
HiveQL - Select-Where
Hive 查询语言 (HiveQL) 是 Hive 处理和分析 Metastore 中结构化数据的查询语言。本章解释了如何将 SELECT 语句与 WHERE 子句结合使用。
SELECT 语句用于从表中检索数据。WHERE 子句类似于一个条件。它使用条件过滤数据，并为你提供有限的结果。内置运算符和函数生成一个表达式，该表达式满足条件。
Syntax
下面给出了 SELECT 查询的语法：
SELECT [ALL | DISTINCT] select_expr, select_expr, ...
FROM table_reference
[WHERE where_condition]
[GROUP BY col_list]
[HAVING having_condition]
[CLUSTER BY col_list | [DISTRIBUTE BY col_list] [SORT BY col_list]]
[LIMIT number];Example
我们以一个 SELECT…WHERE 子句的示例为例。假设我们有如下的雇员表，其中字段名为 Id、Name、Salary、Designation 和 Dept。生成一个查询来检索工资超过 30000 卢比的员工详细信息。
+------+--------------+-------------+-------------------+--------+
| ID | Name | Salary | Designation | Dept |
+------+--------------+-------------+-------------------+--------+
|1201 | Gopal | 45000 | Technical manager | TP |
|1202 | Manisha | 45000 | Proofreader | PR |
|1203 | Masthanvali | 40000 | Technical writer | TP |
|1204 | Krian | 40000 | Hr Admin | HR |
|1205 | Kranthi | 30000 | Op Admin | Admin |
+------+--------------+-------------+-------------------+--------+以下查询使用上述场景检索员工详细信息：
hive> SELECT * FROM employee WHERE salary>30000;在成功执行查询后，您可以看到以下响应：
+------+--------------+-------------+-------------------+--------+
| ID | Name | Salary | Designation | Dept |
+------+--------------+-------------+-------------------+--------+
|1201 | Gopal | 45000 | Technical manager | TP |
|1202 | Manisha | 45000 | Proofreader | PR |
|1203 | Masthanvali | 40000 | Technical writer | TP |
|1204 | Krian | 40000 | Hr Admin | HR |
+------+--------------+-------------+-------------------+--------+JDBC Program
以下 JDBC 程序将 where 子句应用于给定示例。
import java.sql.SQLException;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.Statement;
import java.sql.DriverManager;
public class HiveQLWhere {
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
Resultset res = stmt.executeQuery("SELECT * FROM employee WHERE salary>30000;");
System.out.println("Result:");
System.out.println(" ID \t Name \t Salary \t Designation \t Dept ");
while (res.next()) {
System.out.println(res.getInt(1) + " " + res.getString(2) + " " + res.getDouble(3) + " " + res.getString(4) + " " + res.getString(5));
}
con.close();
}
}将程序保存到名为 HiveQLWhere.java 的文件中。使用以下命令编译并执行此程序。
$ javac HiveQLWhere.java
$ java HiveQLWhere