序言
我们在 Apache Calcite 动态数据管理框架介绍 介绍了 calcite 的基本功能，本文一起来看一下如何实现一个 csv 的 sql 查询。
入门例子
依赖
4.0.0
org.example
calcite-learn
1.0-SNAPSHOT
pom
calcite-learn-basic
8
8
UTF-8
1.20.0
org.apache.calcite
calcite-core
${calcite.version}
org.apache.calcite
calcite-example-csv
${calcite.version}
org.apache.maven.plugins
maven-compiler-plugin
3.8.1
1.8
1.8
测试 csv
创建文件夹：
D:\github\calcite-learn\calcite-learn-basic\src\main\resources\csv下面防对应的测试 csv 文件：
- depts.csv
EMPNO:long,NAME:string,DEPTNO:int,GENDER:string,CITY:string,EMPID:int,AGE:int,SLACKER:boolean,MANAGER:boolean,JOINEDAT:date
100,"Fred",10,,,30,25,true,false,"1996-08-03"
110,"Eric",20,"M","San Francisco",3,80,,false,"2001-01-01"
110,"John",40,"M","Vancouver",2,,false,true,"2002-05-03"
120,"Wilma",20,"F",,1,5,,true,"2005-09-07"
130,"Alice",40,"F","Vancouver",2,,false,true,"2007-01-01"测试类
package com.github.houbb.calcite.learn.basic;
import org.apache.calcite.adapter.csv.CsvSchema;
import org.apache.calcite.adapter.csv.CsvTable;
import org.apache.calcite.jdbc.CalciteConnection;
import org.apache.calcite.schema.SchemaPlus;
import java.io.File;
import java.sql.*;
import java.util.Properties;
public class CsvDemo {
public static void main(String[] args) throws Exception {
// 0.获取csv文件的路径，注意获取到文件所在上层路径就可以了
String path = "D:\\github\\calcite-learn\\calcite-learn-basic\\src\\main\\resources\\csv\\";
// 1.构建CsvSchema对象，在Calcite中，不同数据源对应不同Schema，比如CsvSchema、DruidSchema、ElasticsearchSchema等
CsvSchema csvSchema = new CsvSchema(new File(path), CsvTable.Flavor.SCANNABLE);
// 2.构建Connection
// 2.1 设置连接参数
Properties info = new Properties();
// 不区分sql大小写
info.setProperty("caseSensitive", "false");
// 2.2 获取标准的JDBC Connection
Connection connection = DriverManager.getConnection("jdbc:calcite:", info);
// 2.3 获取Calcite封装的Connection
CalciteConnection calciteConnection = connection.unwrap(CalciteConnection.class);
// 3.构建RootSchema，在Calcite中，RootSchema是所有数据源schema的parent，多个不同数据源schema可以挂在同一个RootSchema下
// 以实现查询不同数据源的目的
SchemaPlus rootSchema = calciteConnection.getRootSchema();
// 4.将不同数据源schema挂载到RootSchema，这里添加CsvSchema
rootSchema.add("csv", csvSchema);
// 5.执行SQL查询，通过SQL方式访问csv文件
String sql = "select * from csv.depts";
Statement statement = calciteConnection.createStatement();
ResultSet resultSet = statement.executeQuery(sql);
// 6.遍历打印查询结果集
printResultSet(resultSet);
}
public static void printResultSet(ResultSet resultSet) throws SQLException {
// 获取 ResultSet 元数据
ResultSetMetaData metaData = resultSet.getMetaData();
// 获取列数
int columnCount = metaData.getColumnCount();
System.out.println("Number of columns: " + columnCount);
// 遍历 ResultSet 并打印结果
while (resultSet.next()) {
// 遍历每一列并打印
for (int i = 1; i <= columnCount; i++) {
String columnName = metaData.getColumnName(i);
String columnValue = resultSet.getString(i);
System.out.println(columnName + ": " + columnValue);
}
System.out.println(); // 换行
}
}
}测试效果
Number of columns: 10
EMPNO: 100
NAME: Fred
DEPTNO: 10
GENDER:
CITY:
EMPID: 30
AGE: 25
SLACKER: true
MANAGER: false
JOINEDAT: 1996-08-03
EMPNO: 110
NAME: Eric
DEPTNO: 20
GENDER: M
CITY: San Francisco
EMPID: 3
AGE: 80
SLACKER: null
MANAGER: false
JOINEDAT: 2001-01-01
EMPNO: 110
NAME: John
DEPTNO: 40
GENDER: M
CITY: Vancouver
EMPID: 2
AGE: null
SLACKER: false
MANAGER: true
JOINEDAT: 2002-05-03
EMPNO: 120
NAME: Wilma
DEPTNO: 20
GENDER: F
CITY:
EMPID: 1
AGE: 5
SLACKER: null
MANAGER: true
JOINEDAT: 2005-09-07
EMPNO: 130
NAME: Alice
DEPTNO: 40
GENDER: F
CITY: Vancouver
EMPID: 2
AGE: null
SLACKER: false
MANAGER: true
JOINEDAT: 2007-01-01参考资料
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