flink1.12.x Table API 和 SQL：从kafka读取数据，聚合查询，写入到elasticsearch

maven <dependency>中的<scope>：import、test、system

future versions of Elasticsearch will require Java 11; your Java version from does not meet this requirement

TableException: EXPR$1 is not found in PojoType<test.TestTable读取文件_分组sql$Order, fields = [name: String, price: Double, username: String]>

springmvc 下载文件、中文乱码

easyexcel java操作excel

SpringMVC返回json将null转为空字符串

mysql-一对多查询，一行显示（group_concat）

oracle-nvl()判断NULL取另一个值

flink1.12.x Transformation-split拆分、select和Side Outputs（未完）