语法
select_statementUNION ALLselect_statement;
UNION ALL 语句将两个流合并。要求两个流的字段完全一致，包括字段类型、字段顺序。
注意: 实时计算同样支持 UNION 函数。UNION ALL 允许重复值，UNION 不允许重复值。在Flink 底层，UNION 是 UNION ALL + Distinct , 因此 UNION 运行效率比较低，一般不推荐使用 UNION。
示例一
SELECT *FROM ((SELECT user FROM 表名 WHERE a % 2 = 0)UNION ALL(SELECT user FROM 表名 WHERE b = 0));
示例二
测试数据
test_source_union1：
| a(varchar) | b(bigint) | c(bigint) |
|---|---|---|
| test1 | 1 | 10 |
test_source_union2：
| a(varchar) | b(bigint) | c(bigint) |
|---|---|---|
| test1 | 1 | 10 |
| test2 | 2 | 20 |
test_source_union3：
| a(varchar) | b(bigint) | c(bigint) |
|---|---|---|
| test1 | 1 | 10 |
| test2 | 2 | 20 |
| test1 | 1 | 10 |
测试语句
create table test_source_union1 (a varchar,b bigint,c bigint) WITH (type='datahub',endpoint='',accessId='',accessKey='',projectName='',topic='',project='');create table test_source_union2 (a varchar,b bigint,c bigint) WITH (type='datahub',endpoint='',accessId='',accessKey='',projectName='',topic='',project='');create table test_source_union3 (a varchar,b bigint,c bigint) WITH (type='datahub',endpoint='',accessId='',accessKey='',projectName='',topic='',project='');create table test_result_union (d VARCHAR,e BIGINT,f BIGINT,primary key(d)) WITH (type='rds',url='',username='',password='',tableName='');INSERT into test_result_unionSELECTa,sum(b),sum(c)FROM(SELECT * from test_source_union1UNION ALLSELECT * from test_source_union2UNION ALLSELECT * from test_source_union3)tGROUP BY a;
测试结果
| d(varchar) | e(bigint) | f(bigint) |
|---|---|---|
| test1 | 1 | 10 |
| test2 | 2 | 20 |
| test1 | 2 | 20 |
| test1 | 3 | 30 |
| test2 | 4 | 40 |
| test1 | 4 | 40 |
本文转自实时计算——
UNION ALL语句
