Hive查询语言(HiveQL)是一种查询语言,Hive处理在Metastore分析结构化数据。本章介绍了如何使用SELECT语句的WHERE子句。
SELECT语句用来从表中检索的数据。 WHERE子句中的工作原理类似于一个条件。它使用这个条件过滤数据，并返回给出一个有限的结果。内置运算符和函数产生一个表达式，满足以下条件。
语法
下面给出的是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];
示例
让我们举个例子SELECT ... WHERE子句。假设employee表有如下 Id, Name, Salary, Designation, 和 Dept等字段，生成一个查询检索超过30000薪水的员工详细信息。
+------+--------------+-------------+-------------------+--------+ | 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 | +------+--------------+-------------+-------------------+--------+
下面的查询检索使用上述业务情景的员工详细信息：
hive> SELECT * FROM employee WHERE salary>30000;
成功执行查询后，能看到以下回应：
+------+--------------+-------------+-------------------+--------+ | 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 程序
在JDBC程序应用，其中针对给定的例子如下子句。
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();
}
}
保存程序在一个名为HiveQLWhere.java文件。使用下面的命令来编译和执行这个程序。
$ javac HiveQLWhere.java $ java HiveQLWhere
输出：
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
