SQL操作：Select (SelectStreamOp)

Java 类名：com.alibaba.alink.operator.stream.sql.SelectStreamOp
Python 类名：SelectStreamOp

功能介绍

对流式数据进行sql的SELECT操作。

使用方式

SELECT 语句中支持的内置函数可以参考 Flink
对应版本的官方文档： System (Built-in) Functions
。 但需要注意，有些内置函数在旧 planner
中不支持，在这里列出：Unsupported Built-In Functions
。

参数说明

| 名称 | 中文名称 | 描述 | 类型 | 是否必须？ | 取值范围 | 默认值 | | —- | —- | —- | —- | —- | —- | —- |

| clause | 运算语句 | 运算语句 | String | ✓ | | |

代码示例

Python 代码

df = pd.DataFrame([
    ['Ohio', 2000, 1.5],
    ['Ohio', 2001, 1.7],
    ['Ohio', 2002, 3.6],
    ['Nevada', 2001, 2.4],
    ['Nevada', 2002, 2.9],
    ['Nevada', 2003, 3.2]
])
stream_data = StreamOperator.fromDataframe(df, schemaStr='f1 string, f2 bigint, f3 double')
op = SelectStreamOp().setClause('f1 as river')
stream_data = stream_data.link(op)
stream_data.print()
StreamOperator.execute()

Java 代码

import org.apache.flink.types.Row;
import com.alibaba.alink.operator.stream.StreamOperator;
import com.alibaba.alink.operator.stream.source.MemSourceStreamOp;
import com.alibaba.alink.operator.stream.sql.SelectStreamOp;
import org.junit.Test;
import java.util.Arrays;
import java.util.List;
public class SelectStreamOpTest {
    @Test
    public void testSelectStreamOp() throws Exception {
        List <Row> df = Arrays.asList(
            Row.of("Ohio", 2000, 1.5),
            Row.of("Ohio", 2001, 1.7),
            Row.of("Ohio", 2002, 3.6),
            Row.of("Nevada", 2001, 2.4),
            Row.of("Nevada", 2002, 2.9),
            Row.of("Nevada", 2003, 3.2)
        );
        StreamOperator <?> stream_data = new MemSourceStreamOp(df, "f1 string, f2 int, f3 double");
        StreamOperator <?> op = new SelectStreamOp().setClause("f1 as river");
        stream_data = stream_data.link(op);
        stream_data.print();
        StreamOperator.execute();
    }
}

运行结果

river

Ohio
Ohio
Nevada
Ohio
Nevada
Nevada