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‎202309/20230928_02.md‎

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## DuckDB 语法糖: Reusable column aliases
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### 作者
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digoal
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### 日期
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2023-09-28
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### 标签
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PostgreSQL , PolarDB , duckdb , 语法糖
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----
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## 背景
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duckdb增加了很多SQL语法糖, 目标是要让用户可以随心所欲的写SQL.
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https://duckdb.org/2023/08/23/even-friendlier-sql.html
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Reusable column aliases
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在查询中可以使用前面已经定义过的column alias.
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旧的用法:
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```
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select
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'These are the voyages of the starship Enterprise...' AS intro,
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instr('These are the voyages of the starship Enterprise...', 'starship') AS starship_loc
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substr('These are the voyages of the starship Enterprise...', instr('These are the voyages of the starship Enterprise...', 'starship') + len('starship') + 1) AS trimmed_intro;
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```
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```
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WITH intro_cte AS (
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SELECT
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'These are the voyages of the starship Enterprise...' AS intro
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), starship_loc_cte AS (
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SELECT
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intro,
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instr(intro, 'starship') AS starship_loc
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FROM intro_cte
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)
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SELECT
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intro,
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starship_loc,
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substr(intro, starship_loc + len('starship') + 1) AS trimmed_intro
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FROM starship_loc_cte;
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```
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新用法:
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```
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SELECT
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'These are the voyages of the starship Enterprise...' AS intro,
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instr(intro, 'starship') AS starship_loc,
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substr(intro, starship_loc + len('starship') + 1) AS trimmed_intro;
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```
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intro | starship_loc | trimmed_intro
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---|---|---
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These are the voyages of the starship Enterprise…| 30| Enterprise…
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#### [期望 PostgreSQL|开源PolarDB 增加什么功能?](https://github.com/digoal/blog/issues/76 "269ac3d1c492e938c0191101c7238216")
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#### [PolarDB 云原生分布式开源数据库](https://github.com/ApsaraDB "57258f76c37864c6e6d23383d05714ea")
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#### [PolarDB 学习图谱: 训练营、培训认证、在线互动实验、解决方案、内核开发公开课、生态合作、写心得拿奖品](https://www.aliyun.com/database/openpolardb/activity "8642f60e04ed0c814bf9cb9677976bd4")
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#### [PostgreSQL 解决方案集合](../201706/20170601_02.md "40cff096e9ed7122c512b35d8561d9c8")
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#### [德哥 / digoal's github - 公益是一辈子的事.](https://github.com/digoal/blog/blob/master/README.md "22709685feb7cab07d30f30387f0a9ae")
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![digoal's wechat](../pic/digoal_weixin.jpg "f7ad92eeba24523fd47a6e1a0e691b59")
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‎202309/20230928_03.md‎

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## DuckDB 语法糖: Dynamic column selection 支持通配符,exclude,replace,lambda 等动态列选择|值替换|列选择
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### 作者
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digoal
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### 日期
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2023-09-28
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### 标签
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PostgreSQL , PolarDB , duckdb , 语法糖
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----
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## 背景
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duckdb增加了很多SQL语法糖, 目标是要让用户可以随心所欲的写SQL.
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https://duckdb.org/2023/08/23/even-friendlier-sql.html
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Dynamic column selection 支持通配符,exclude等动态列选择
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加载一些测试数据:
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```
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INSTALL httpfs;
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LOAD httpfs;
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CREATE TABLE trek_facts AS
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SELECT * FROM 'https://raw.githubusercontent.com/Alex-Monahan/example_datasets/main/Star_Trek-Season_1.csv';
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DESCRIBE trek_facts;
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```
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结构如下:
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column_name | column_type | null | key | default |extra
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---|---|---|---|---|---
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season_num |BIGINT |YES |NULL |NULL |NULL
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episode_num |BIGINT |YES |NULL |NULL |NULL
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aired_date |DATE |YES |NULL |NULL |NULL
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cnt_kirk_hookups |BIGINT |YES |NULL |NULL |NULL
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cnt_downed_redshirts |BIGINT |YES |NULL |NULL |NULL
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bool_aliens_almost_took_over_planet |BIGINT |YES |NULL |NULL |NULL
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bool_aliens_almost_took_over_enterprise |BIGINT |YES |NULL |NULL |NULL
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cnt_vulcan_nerve_pinch |BIGINT |YES |NULL |NULL |NULL
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cnt_warp_speed_orders |BIGINT |YES |NULL |NULL |NULL
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highest_warp_speed_issued |BIGINT |YES |NULL |NULL |NULL
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bool_hand_phasers_fired |BIGINT |YES |NULL |NULL |NULL
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bool_ship_phasers_fired |BIGINT |YES |NULL |NULL |NULL
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bool_ship_photon_torpedos_fired |BIGINT |YES |NULL |NULL |NULL
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cnt_transporter_pax |BIGINT |YES |NULL |NULL |NULL
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cnt_damn_it_jim_quote |BIGINT |YES |NULL |NULL |NULL
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cnt_im_givin_her_all_shes_got_quote |BIGINT |YES |NULL |NULL |NULL
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cnt_highly_illogical_quote |BIGINT |YES |NULL |NULL |NULL
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bool_enterprise_saved_the_day |BIGINT |YES |NULL |NULL |NULL
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使用columns(正则)
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```
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SELECT
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episode_num,
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COLUMNS('.*warp.*')
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FROM trek_facts;
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```
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episode_num | cnt_warp_speed_orders | highest_warp_speed_issued
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---|---|---
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0 |1 |1
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… |… |…
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27 |1 |1
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columns可以和其他函数结合使用
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```
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SELECT
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MAX(COLUMNS('.*warp.*'))
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FROM trek_facts;
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```
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max(trek_facts.cnt_warp_speed_orders) |max(trek_facts.highest_warp_speed_issued)
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---|---
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5 | 8
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可以放在where中进行计算, 匹配多列相当于and
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```
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SELECT
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episode_num,
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COLUMNS('.*warp.*')
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FROM trek_facts
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WHERE
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COLUMNS('.*warp.*') >= 2;
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-- cnt_warp_speed_orders >= 2
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-- AND
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-- highest_warp_speed_issued >= 2
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```
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episode_num |cnt_warp_speed_orders |highest_warp_speed_issued
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---|---|---
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14 |3 |7
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17 |2 |7
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18 |2 |8
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29 |2 |8
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COLUMNS() with EXCLUDE and REPLACE
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```
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-- 排除 season_num 列名.
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SELECT
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MAX(COLUMNS(* EXCLUDE season_num))
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FROM trek_facts;
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```
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替换列
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```
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-- 使用aired_date::timestamp 替换 aired_date
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SELECT
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MAX(COLUMNS(* REPLACE aired_date::timestamp AS aired_date))
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FROM trek_facts;
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```
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COLUMNS() with lambda functions
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```
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-- 列名符合like ...
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SELECT
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episode_num,
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COLUMNS(col -> col LIKE '%warp%')
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FROM trek_facts
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WHERE
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COLUMNS(col -> col LIKE '%warp%') >= 2;
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```
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episode_num | cnt_warp_speed_orders | highest_warp_speed_issued
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---|---|---
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14 |3 |7
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17 |2 |7
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18 |2 |8
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29 |2 |8
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#### [期望 PostgreSQL|开源PolarDB 增加什么功能?](https://github.com/digoal/blog/issues/76 "269ac3d1c492e938c0191101c7238216")
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#### [PolarDB 云原生分布式开源数据库](https://github.com/ApsaraDB "57258f76c37864c6e6d23383d05714ea")
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#### [PolarDB 学习图谱: 训练营、培训认证、在线互动实验、解决方案、内核开发公开课、生态合作、写心得拿奖品](https://www.aliyun.com/database/openpolardb/activity "8642f60e04ed0c814bf9cb9677976bd4")
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#### [PostgreSQL 解决方案集合](../201706/20170601_02.md "40cff096e9ed7122c512b35d8561d9c8")
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#### [德哥 / digoal's github - 公益是一辈子的事.](https://github.com/digoal/blog/blob/master/README.md "22709685feb7cab07d30f30387f0a9ae")
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![digoal's wechat](../pic/digoal_weixin.jpg "f7ad92eeba24523fd47a6e1a0e691b59")
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‎202309/20230928_04.md‎

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## DuckDB 语法糖: Automatic JSON to nested types conversion
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### 作者
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digoal
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### 日期
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2023-09-28
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### 标签
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PostgreSQL , PolarDB , duckdb , 语法糖
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----
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## 背景
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duckdb增加了很多SQL语法糖, 目标是要让用户可以随心所欲的写SQL.
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https://duckdb.org/2023/08/23/even-friendlier-sql.html
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Automatic JSON to nested types conversion , 支持自动识别JSON
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```
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INSTALL httpfs;
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LOAD httpfs;
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INSTALL json;
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LOAD json;
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SELECT
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starfleet[10].model AS starship
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FROM 'https://raw.githubusercontent.com/vlad-saling/star-trek-ipsum/master/src/content/content.json';
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```
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```
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starship
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USS Farragut - NCC-1647 - Ship on which James Kirk served as a phaser station operator. Attacked by the Dikironium Cloud Creature, killing half the crew. ad.
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```
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#### [期望 PostgreSQL|开源PolarDB 增加什么功能?](https://github.com/digoal/blog/issues/76 "269ac3d1c492e938c0191101c7238216")
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#### [PolarDB 云原生分布式开源数据库](https://github.com/ApsaraDB "57258f76c37864c6e6d23383d05714ea")
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#### [PolarDB 学习图谱: 训练营、培训认证、在线互动实验、解决方案、内核开发公开课、生态合作、写心得拿奖品](https://www.aliyun.com/database/openpolardb/activity "8642f60e04ed0c814bf9cb9677976bd4")
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#### [PostgreSQL 解决方案集合](../201706/20170601_02.md "40cff096e9ed7122c512b35d8561d9c8")
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#### [德哥 / digoal's github - 公益是一辈子的事.](https://github.com/digoal/blog/blob/master/README.md "22709685feb7cab07d30f30387f0a9ae")
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![digoal's wechat](../pic/digoal_weixin.jpg "f7ad92eeba24523fd47a6e1a0e691b59")
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‎202309/20230928_05.md‎

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## DuckDB 语法糖: FROM first in SELECT statements
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### 作者
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digoal
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### 日期
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2023-09-28
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### 标签
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PostgreSQL , PolarDB , duckdb , 语法糖
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----
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## 背景
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duckdb增加了很多SQL语法糖, 目标是要让用户可以随心所欲的写SQL.
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https://duckdb.org/2023/08/23/even-friendlier-sql.html
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FROM first in SELECT statements
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```
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FROM my_table SELECT my_column;
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```
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```
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FROM my_table;
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-- 相当于 SELECT * FROM my_table
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```
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```
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COPY (FROM trek_facts) TO 'phaser_filled_facts.parquet';
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```
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#### [期望 PostgreSQL|开源PolarDB 增加什么功能?](https://github.com/digoal/blog/issues/76 "269ac3d1c492e938c0191101c7238216")
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#### [PolarDB 云原生分布式开源数据库](https://github.com/ApsaraDB "57258f76c37864c6e6d23383d05714ea")
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#### [PolarDB 学习图谱: 训练营、培训认证、在线互动实验、解决方案、内核开发公开课、生态合作、写心得拿奖品](https://www.aliyun.com/database/openpolardb/activity "8642f60e04ed0c814bf9cb9677976bd4")
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#### [PostgreSQL 解决方案集合](../201706/20170601_02.md "40cff096e9ed7122c512b35d8561d9c8")
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#### [德哥 / digoal's github - 公益是一辈子的事.](https://github.com/digoal/blog/blob/master/README.md "22709685feb7cab07d30f30387f0a9ae")
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![digoal's wechat](../pic/digoal_weixin.jpg "f7ad92eeba24523fd47a6e1a0e691b59")
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