95 lines
2.3 KiB
Markdown
95 lines
2.3 KiB
Markdown
---
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{
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"title": "Lateral View",
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"language": "zh-CN"
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}
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---
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<!--
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Licensed to the Apache Software Foundation (ASF) under one
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or more contributor license agreements. See the NOTICE file
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distributed with this work for additional information
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regarding copyright ownership. The ASF licenses this file
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to you under the Apache License, Version 2.0 (the
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"License"); you may not use this file except in compliance
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with the License. You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing,
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software distributed under the License is distributed on an
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"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
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KIND, either express or implied. See the License for the
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specific language governing permissions and limitations
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under the License.
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-->
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# Lateral View
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## description
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Lateral view 语法可以搭配 Table Function，完成将一行数据扩展成多行（列转行）的需求。
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语法：
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```
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...
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FROM table_name
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lateral_view_ref[ lateral_view_ref ...]
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lateral_view_ref:
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LATERAL VIEW table_function(...) view_alias as col_name
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```
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Lateral view 子句必须跟随在表名或子查询之后。可以包含多个 Lateral view 子句。`view_alias` 是对应 Lateral View 的名称。`col_name` 是表函数 `table_function` 产出的列名。
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目前支持的表函数：
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1. `explode_split`
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2. `explode_bitmap`
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3. `explode_json_array`
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具体函数说明可参阅对应语法帮助文档。
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table 中的数据会和各个 Lateral View 产生的结果集做笛卡尔积后返回上层。
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## example
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这里只给出 Lateral View 的语法示例，具体含义和产出的结果说明，可参阅对应表函数帮助文档。
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1.
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```
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select k1, e1 from tbl1
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lateral view explode_split(v1, ',') tmp1 as e1 where e1 = "abc";
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```
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2.
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```
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select k1, e1, e2 from tbl2
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lateral view explode_split(v1, ',') tmp1 as e1
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lateral view explode_bitmap(bitmap1) tmp2 as e2
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where e2 > 3;
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```
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3.
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```
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select k1, e1, e2 from tbl3
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lateral view explode_json_array_int("[1,2,3]") tmp1 as e1
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lateral view explode_bitmap(bitmap_from_string("4,5,6")) tmp2 as e2;
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```
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4.
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```
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select k1, e1 from (select k1, bitmap_union(members) as x from tbl1 where k1=10000 group by k1)tmp1
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lateral view explode_bitmap(x) tmp2 as e1;
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```
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## keyword
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LATERAL, VIEW
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