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# Proposed changes Issue Number: close #6238 Co-authored-by: HappenLee <happenlee@hotmail.com> Co-authored-by: stdpain <34912776+stdpain@users.noreply.github.com> Co-authored-by: Zhengguo Yang <yangzhgg@gmail.com> Co-authored-by: wangbo <506340561@qq.com> Co-authored-by: emmymiao87 <522274284@qq.com> Co-authored-by: Pxl <952130278@qq.com> Co-authored-by: zhangstar333 <87313068+zhangstar333@users.noreply.github.com> Co-authored-by: thinker <zchw100@qq.com> Co-authored-by: Zeno Yang <1521564989@qq.com> Co-authored-by: Wang Shuo <wangshuo128@gmail.com> Co-authored-by: zhoubintao <35688959+zbtzbtzbt@users.noreply.github.com> Co-authored-by: Gabriel <gabrielleebuaa@gmail.com> Co-authored-by: xinghuayu007 <1450306854@qq.com> Co-authored-by: weizuo93 <weizuo@apache.org> Co-authored-by: yiguolei <guoleiyi@tencent.com> Co-authored-by: anneji-dev <85534151+anneji-dev@users.noreply.github.com> Co-authored-by: awakeljw <993007281@qq.com> Co-authored-by: taberylyang <95272637+taberylyang@users.noreply.github.com> Co-authored-by: Cui Kaifeng <48012748+azurenake@users.noreply.github.com> ## Problem Summary: ### 1. Some code from clickhouse **ClickHouse is an excellent implementation of the vectorized execution engine database, so here we have referenced and learned a lot from its excellent implementation in terms of data structure and function implementation. We are based on ClickHouse v19.16.2.2 and would like to thank the ClickHouse community and developers.** The following comment has been added to the code from Clickhouse, eg: // This file is copied from // https://github.com/ClickHouse/ClickHouse/blob/master/src/Interpreters/AggregationCommon.h // and modified by Doris ### 2. Support exec node and query: * vaggregation_node * vanalytic_eval_node * vassert_num_rows_node * vblocking_join_node * vcross_join_node * vempty_set_node * ves_http_scan_node * vexcept_node * vexchange_node * vintersect_node * vmysql_scan_node * vodbc_scan_node * volap_scan_node * vrepeat_node * vschema_scan_node * vselect_node * vset_operation_node * vsort_node * vunion_node * vhash_join_node You can run exec engine of SSB/TPCH and 70% TPCDS stand query test set. ### 3. Data Model Vec Exec Engine Support **Dup/Agg/Unq** table, Support Block Reader Vectorized. Segment Vec is working in process. ### 4. How to use 1. Set the environment variable `set enable_vectorized_engine = true; `(required) 2. Set the environment variable `set batch_size = 4096; ` (recommended) ### 5. Some diff from origin exec engine https://github.com/doris-vectorized/doris-vectorized/issues/294 ## Checklist(Required) 1. Does it affect the original behavior: (No) 2. Has unit tests been added: (Yes) 3. Has document been added or modified: (No) 4. Does it need to update dependencies: (No) 5. Are there any changes that cannot be rolled back: (Yes)
63 lines
1.6 KiB
Markdown
63 lines
1.6 KiB
Markdown
---
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{
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"title": "coalesce",
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"language": "en"
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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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# coalesce
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## Description
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### Syntax
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`VARCHAR coalesce(VARCHAR, ...)`
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`...`
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`INT coalesce(INT, ...)`
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` coalesce ` function will return the first not null value. If it's all value is null, return null
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## example
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```
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MySQL> select coalesce(1,null,2);
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+----------------------+
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| coalesce(1, NULL, 2) |
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+----------------------+
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| 1 |
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+----------------------+
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MySQL> select coalesce(null,"asd",1);
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+--------------------------+
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| coalesce(NULL, 'asd', 1) |
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+--------------------------+
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| asd |
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+--------------------------+
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MySQL> select coalesce(null,null,null);
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+----------------------------+
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| coalesce(NULL, NULL, NULL) |
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+----------------------------+
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| NULL |
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+----------------------------+
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```
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## keyword
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coalesce
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