PostgreSQL 中的游标循环

Question

以下代码是 PostgreSQL 9.0 中的游标。我想通过加入多个 table 来获取我的记录，并且我正在从该加入中获取 JSON 数据。

所以我想循环这些记录并使用类似

的查询来解析 json

SELECT "Dump"->'activities-steps'->0->'value' as "steps"
FROM "ActivitySessionDump" where "Id"=42594321345021288

然后我必须从这个查询中获取数据并插入到其他table如

insert to table name (key,value);

所以我准备了一个只读游标来完成这个任务

begin work;

DECLARE 
sessionids INSENSITIVE no scroll CURSOR FOR 
SELECT asn."Id",asn."UserId",asn."ActivityId",ad."Dump"
  FROM "ActivitySession" as asn inner join "ActivitySessionDump" as ad 
  on asn."Id"=ad."ActivitySessionId" 
  where asn."CreatedAt" between now() - interval '5 hours' and now() and asn."ActivityId"=1 
for read only;
---- i want her loop should start and i will parse a json Dump by executing query--------

--------insert record to another table---------------

---end loop-----------
FETCH next FROM sessionids;
CLOSE sessionids;
COMMIT WORK;

真的有帮助appreciated.Thanks

Answer 1

由于无法在 SQL 中循环，因此您必须使用 PL/pgSQL，例如使用 DO 语句。

在您的情况下，可能如下所示：

DO
$$DECLARE
   asn_id ...;
   asn_userid ...;
   ...
   c refcursor;
BEGIN
   /* assign the SQL cursor to the refcursor variable */
   c := 'sessionids';

   LOOP
      FETCH c INTO asn_id, asn_userid, ...;
      IF NOT FOUND THEN EXIT; END IF;

      /* process the result row */

   END LOOP;
END;$$;

当然在SQL中声明游标，在PL/pgSQL中使用就有点别扭了。将语句放在 FOR 循环中可能会更好：

FOR asn_id, asn_userid, ... IN
  SELECT ...
LOOP

   /* process the result row */

END LOOP;

也许您甚至可以将整个事情压缩到一个 INSERT 语句中，这样效率最高：

INSERT INTO ...
   (SELECT ...);

Answer 2

这是我的问题的代码，我无法 EXECUTE 'SELECT rec."Dump"::json#>''{activities-steps,0}''->>''value'' 作为步骤' INTO jsonrec;线;

SELECT '{"activities-steps":[{"dateTime":"2016-10-17","value":"4023"}]}'::json#>'{activities-steps,0}'->>'value'作为步数；我在哪里可以在控制台中执行此代码。

但内部函数我不能。

CREATE OR REPLACE FUNCTION ThirdPartyDataParse()
RETURNS text AS $$
DECLARE 
sessionid NO SCROLL CURSOR FOR SELECT asn."Id",asn."UserId",asn."ActivityId",pd."DataSourceId",ad."Dump"::TEXT
   FROM "Development"."ActivitySession" as asn inner join "Development"."PersonDataSource" as pd on pd."UserId" = asn."UserId" inner join "Development"."ActivitySessionDump" as ad 
   on asn."Id"=ad."ActivitySessionId" where asn."CreatedAt" between now() - interval '5 days' and now() and asn."ActivityId"=1  and pd."DataSourceId"=1 for read only;
titles TEXT DEFAULT '';
rec record;
jsonrec record;
 BEGIN
 OPEN sessionid;
loop

FETCH sessionid INTO rec;
--raise notice '%d',rec."UserId";
   if not found then
        exit ;
   end if;
 EXECUTE 'SELECT rec."Dump"::json#>''{activities-steps,0}''->>''value'' as steps ' INTO jsonrec;
titles := titles || ',' || jsonrec."steps";
end loop;
return titles;
END;
$$ LANGUAGE plpgsql;

Answer 3

据我所知，循环或函数是不必要的。它可以替换为使用字符串聚合的简单查询：

SELECT string_agg("Dump"->'activities-steps'->0->'value', ',') as steps 
FROM "ActivitySessionDump" d
WHERE d."ActivitySessionId" IN (SELECT asn."Id"
                                FROM "ActivitySession" as asn 
                                  join "PersonDataSource" as pd on pd."UserId" = asn."UserId" 
                                where asn."CreatedAt" between now() - interval '5 days' and now() 
                                  and asn."ActivityId" = 1  
                                  and pd."DataSourceId" = 1);

无关，但是：你应该真的避免那些可怕的引用标识符

PostgreSQL 中的游标循环

cursor loop in PostgreSQL

json

postgresql

plpgsql

database-cursor