AI代码解释 create tablet1(id1 int,id2varchar(64));insert into t1values(1,’nanjing’),(1,’suzhou’),(2,’xingtai’),(2,’shijiazhuang’);select id1,string_agg(id2,’,’)group by id1;id1|string_agg---1|nanjing,suzhou2|xingtai,shijiazhuang array_agg函数和string_agg函数类似,最主要...
[ GROUP BY grouping_element [, ...] ] [ HAVING condition [, ...] ] [ WINDOW window_name AS ( window_definition ) [, ...] ] [ { UNION | INTERSECT | EXCEPT } [ ALL | DISTINCT ] select ] [ ORDER BY expression [ ASC | DESC | USING operator ] [ NULLS { FIRST | LAST } ...
createuser examplegroup --no-login 2. 登录Postgres shell并添加examplerole到新组: psql postgres GRANT examplegroup TO examplerole; 3. 从Postgres shell中,验证您的更改\du。您将看到该examplerole用户现在被列为该examplegroup组的成员: postgres=# \du List of roles Role name | Attributes | Member of...
group by 和having: select Department_id, count(*) from Course group by Department_id having count(*) = 4; --哪些部门开设了4门课。 avg和group by: select Department_id, avg(Additional_Fees) from Course group by Department_id; 23.EXISTS select Last_Name, Fist_Name from Instructor I where...
.datname)ASsizefrompg_database;datname|size---+---postgres|8242031csqjxiao|8242031template1|8094211template0|8094211test|8389487(5rows)#selectpg_size_pretty(pg_database_size('test'));//以KB,MB,GB的方式来查看数据库大pg_size_pretty---8193kB(1row)# \q 显示用户 $ psql test# \duListofro...
LINE 1: select current_database; ^test@[local]:5432=#select current_database();current_database ---test(1 row)test@[local]:5432=#select current_user;current_user --- pguser (1 row) postgres@[local]:5432=#select * from pg_database;oid | datname | datdba | encoding | datcollate...
PARTITION BY选项用于定义分区,作用类似于GROUP BY的分组。如果指定了分区选项,窗口函数将会分别针对每个分区单独进行分析;如果省略分区选项,所有的数据作为一个整体进行分析,上文中的示例就是如此。 以下语句按照部门进行分组,分析每个部门的平均月薪: SELECTfirst_name,last_name,department_id,salary,AVG(salary)OVER(...
SELECT * FROM users LIMIT 10; PostgreSQL SELECT * FROM users LIMIT 10; 对比:两者的LIMIT用法一致。 8. 排序结果 MySQL SELECT * FROM users ORDER BY name ASC; PostgreSQL SELECT * FROM users ORDER BY name ASC; 对比:排序语法相同。 9. 连接查询 ...
(1 row) Time: 2166.481 ms (00:02.166) 四核并行 postgres=# set max_parallel_workers_per_gather to 4; SET Time: 0.315 ms postgres=# select count(1) from t_count; count --- 20000000 (1 row) Time: 1162.433 ms (00:01.162) postgres=# not in 中包含了null,结果全为真 postgres...
Greenplum会根据group by的字段的distinct值的比例,考虑是直接重分布数据,还是先在本地聚合后再重分布数据(减少重分布的数据量)。 2、非分布键 distinct 例子, tbl 为 随机分布 postgres=# explain analyze select count(distinct c2) from tbl;QUERY PLAN---Aggregate (cost=1549462.55..1549462.56rows=1width=8...