Flink SQL含有聚合算子时无法直接print

Exception in thread "main" org.apache.flink.table.api.TableException: AppendStreamTableSink doesn't support consuming update and delete changes which is produced by node Rank(strategy=[UndefinedStrategy], rankType=[ROW_NUMBER], rankRange=[rankStart=1, rankEnd=1], partitionBy=[category], orderBy=[sales DESC], select=[category, sales])
    at org.apache.flink.table.planner.plan.optimize.program.FlinkChangelogModeInferenceProgram$SatisfyModifyKindSetTraitVisitor.createNewNode(FlinkChangelogModeInferenceProgram.scala:355)
    at org.apache.flink.table.planner.plan.optimize.program.FlinkChangelogModeInferenceProgram$SatisfyModifyKindSetTrai 

原因：

正常情况下默认使用toAppendStream进行表流转化，而聚合操作涉及delete操作，单纯appendStream无法满足，因此考虑使用RetractStream或UpsertStream。

解决：

使用tableEnvironment.toRetractStream()进行输出 例如：

Table table = tEnv.sqlQuery(
                        "SELECT\n" +
                        "    userName,\n" +
                        "    product,\n" +
                        "    amount\n" +
                        "FROM\n" +
                        "    orders,\n" +
                        "    user_table\n" +
                        "WHERE\n" +
                        "    orders.userId = user_table.userId");
Table table = tEnv.sqlQuery("SELECT userId,sum(amount) as boughtSum " +
                            "FROM orders group by userId");
tEnv.toRetractStream(table, TypeInformation.of(new TypeHint<Tuple2<String, Integer>>() {
})).print();