join - KSQL 加入两个以上的流

Question

在 KSQL 中是否可以连接两个以上的流/表？

例子:

我有三个流:

CREATE STREAM StreamA (id BIGINT, message VARCHAR) WITH 
(KAFKA_TOPIC='TopicA', VALUE_FORMAT='DELIMITED');
CREATE STREAM StreamB (id BIGINT, aid BIGINT, message VARCHAR) WITH . 
(KAFKA_TOPIC='TopicB', VALUE_FORMAT='DELIMITED');
CREATE STREAM StreamC (id BIGINT, bid BIGINT, message VARCHAR) WITH 
(KAFKA_TOPIC='TopicC', VALUE_FORMAT='DELIMITED');

我尝试通过加入这三个流来创建另一个流:

CREATE STREAM ABCStream AS SELECT * FROM StreamA a JOIN 
StreamB b ON b.aid = a.id JOIN StreamC c WITHIN 1 HOURS ON 
c.bid = b.id; 

我得到以下异常:

mismatched input 'JOIN' expecting ';'  
Caused by: org.antlr.v4.runtime.InputMismatchException

Answer 1

不，您只能在 KSQL v5.0 之前的每个查询中连接两个。您需要菊花链式查询，如下所示:

中间流:

CREATE STREAM ABStream AS \
   SELECT * \
     FROM StreamA a \
     JOIN StreamB b \
          ON b.aid = a.id;

多连接流

CREATE STREAM ABCStream AS \
   SELECT * \
     FROM ABStream AB \
     JOIN StreamC c \
          WITHIN 1 HOURS \
          ON c.bid = AB.b_id;