1. 问题一:实现同一字段的多条记录合并到一条记录
方法一:array_agg(expression) 把表达式变成一个数组 一般配合 array_to_string() 函数使用
方法二:string_agg(expression, delimiter) 直接把一个表达式变成字符串,参数二为拼接连接符
方法三:自定义函数
-- 创建合并方法 CREATE AGGREGATE group_concat(anyelement) ( sfunc = array_append, -- 每行的操作函数,将本行append到数组里 stype = anyarray, -- 聚集后返回数组类型 initcond = ‘{}‘ -- 初始化空数组 );
实现SQL
SELECT pd.project_id, array_agg ( pd.file_name ) AS filename FROM a pp LEFT JOIN b pd ON pp.ID = pd.project_id WHERE pp.ENABLEd = ‘T‘ AND pd.ENABLEd = ‘T‘ GROUP BY pd.project_id;
SELECT pd.project_id, string_agg ( pd.file_name,‘,‘ ) AS filename FROM a pp LEFT JOIN b pd ON pp.ID = pd.project_id WHERE pp.ENABLEd = ‘T‘ AND pd.ENABLEd = ‘T‘ GROUP BY pd.project_id;
SELECT
pd.project_id, group_concat ( pd.file_name ) AS filename
FROM
a pp
LEFT JOIN b pd ON pp.ID = pd.project_id
WHERE
pp.ENABLEd = ‘T‘
AND pd.ENABLEd = ‘T‘
GROUP BY
pd.project_id;
补充:array_agg和string_agg函数还有一些其他操作,如排序,去重,按下表取元素等。之后碰上在补充了
问题二:pg中的json字段操作
SELECT
pp.duty :: json -> 0 ->> ‘label‘ AS 负责人
from a pp
当然这个和json的存储格式有关系,因为库中存的是json数组,所以以上方法使用了 0 这个数字去第一个json,如果直接存储的是json则可以省去
问题三:查询父项目及子项目的数据,并排序。这里涉及了pg中的递归函数
with RECURSIVE cte as ( select a.id,cast(a.name as varchar(100)) from tb a union all select k.id,cast(c.name||‘>‘||k.name as varchar(100)) as name from tb k inner join cte c on c.id = k.pid )select id,name from cte ;
解释下该递归的意思,上半部分为父级,下半部分为递归部分,之后将结果作为临时表,还可以和其他表做关联查询。
问题四:pg中分组,并查询每个分组中最大或者最小的值 row_number () over PARTITION BY 相关函数的使用
SELECT *, ROW_NUMBER ( ) OVER ( PARTITION BY a.proc_inst_id ORDER BY last_modified_date DESC NULLS LAST ) t1 FROM a ) AS TEMP WHERE t1 < 2
row_number有点类似虚列,该SQL的意思是按照实力id(proc_inst_id)分组,并按修改时间降序排序,并取出每一组的第一条记录。即最新修改的数据
附上最终SQL,SQL中的表将用a,b,c代替,以及中文注释随意删除了,请不要太在意
-- 创建合并方法 CREATE AGGREGATE group_concat(anyelement) ( sfunc = array_append, -- 每行的操作函数,将本行append到数组里 stype = anyarray, -- 聚集后返回数组类型 initcond = ‘{}‘ -- 初始化空数组 ); WITH RECURSIVE T AS ( SELECT ID , pid, root_id, name, ID :: TEXT AS PATH, 1 AS LEVEL FROM a WHERE pid IS NULL UNION ALL SELECT D.ID, D.pid, D.root_id, d.name, ( T.PATH || ‘/‘ || D.ID ) :: TEXT AS PATH, ( T.LEVEL + 1 ) AS LEVEL FROM a D JOIN T ON D.pid = T.ID ) SELECT (case when T.LEVEL=‘1‘ then ‘一级计划‘ when T.LEVEL=‘2‘ then ‘二级计划‘ when T.LEVEL=‘3‘ then ‘三级计划‘ when T.LEVEL=‘4‘ then ‘四级计划‘ end ) as 计划, parent.name as 父级项目, ( pp.extent_1 :: json ->> 0 ) :: json ->> ‘label‘ AS 功能,-- 二级功能 pp.assist_depts :: json -> 0 ->> ‘label‘ AS 部门, ((case when ppr.operate =‘ADD‘ then ‘新增流程‘ when ppr.operate =‘UPDATE‘ then ‘更新流程‘ when ppr.operate = ‘FINISH‘ then ‘结束流程‘ END ) || ‘/‘ || ( case when ppr.status =‘active‘ then ‘执行中‘ when ppr.status =‘end‘ then ‘已结束‘ when ppr.status =‘cancel‘ then ‘已取消‘ END ) ) as 展示, pr.CONTENT as 日报, sub.filename as 交, pp.ID, pp.pid FROM a pp INNER JOIN T T ON T.ID = pp.ID LEFT JOIN a parent on pp.pid = parent.ID LEFT JOIN ( SELECT plan_id,operate,status FROM ( SELECT *, row_number ( ) over ( PARTITION BY b.proc_inst_id ORDER BY last_modified_date DESC nulls last ) t1 FROM b) AS temp WHERE t1 < 2) ppr ON pp.ID = ppr.plan_id -- 关联表 LEFT JOIN ( SELECT project_id,content FROM ( SELECT *, row_number ( ) over ( PARTITION BY c.project_id ORDER BY last_modified_date DESC nulls last ) t1 FROM c) AS temp WHERE t1 < 2) pr on pr.project_id = pp.id -- 关联表 LEFT JOIN ( SELECT pd.project_id, group_concat ( pd.file_name ) AS filename FROM a pp LEFT JOIN d pd ON pp.ID = pd.project_id -- 关联表 WHERE pp.ENABLEd = ‘T‘ AND pd.ENABLEd = ‘T‘ GROUP BY pd.project_id ) sub ON sub.project_id = pp.ID ORDER BY T.root_id, T."path";