Question

我有一个Postgresql函数，该函数从树中不同的postgresql函数收集数据（数据相同）。但是，应该仅可以基于过滤器运行这三个功能中的某些功能。例子

FROM (SELECT events.id,
            events.slug,
            events.picture_url,
            events.lat,
            events.lng,
            events.user_id,
            events.inserted_at,
            events.updated_at,
            events.geom,
            events.address,
            events.place
            FROM (
              -- DO FILTERING CASE WHEN (filter = 'global' OR filter = 'self') THEN
                  SELECT * from my_events(param_user_id)
              END
              UNION
              -- DO FILTERING CASE WHEN (filter = 'global' OR filter = 'friends') THEN
                --by starting from follows table
                SELECT * FROM follows(param_user_id)
              END
              UNION
              -- DO FILTERING CASE WHEN (filter = 'global' OR filter = 'friends') THEN
                SELECT * FROM friends_events(param_user_id)
              END

            ) AS events ORDER BY events.inserted_at DESC LIMIT limit_count OFFSET limit_count * page
          ) AS e;  END; $function$

过滤器是文本字符串，例如filter =“ function 1”。如果filter =“ function 1”，则仅执行SELECT并忽略其他两个。

If filter = "all" then run all of them. Lambda example
SELECT (<fields>) FROM(
IF filter = "function1" OR filter = "all" then
SELECT <function 1>
IF filter = "function 2" OR filter = "all" THEN

SELECT <function2>

以此类推。

Answer 1

您可以按以下方式使用独立IF：

IF filter = 'func1' THEN
  RETURN QUERY SELECT ...;
ELSEIF filter = 'func2' THEN
  RETURN QUERY SELECT ...;
ELSEIF
  ...
END IF;

或者更好的是，动态查询不重复大的SELECT：

DECLARE
  _str text;
BEGIN
  ...
  --Build dynamic query:
  _str = 'SELECT ... FROM '||filter||'('||param_user_id||') ...';
  --Print to console (Use to debug only)
  RAISE NOTICE '_str = %', _str;
  --Execute and return results
  RETURN QUERY EXECUTE _str;
  ...
END

来自filter的文本与查询串联在一起，并用作函数名称。如果您不能在filter中输入函数名称，请使用

CASE filter WHEN 'func1' THEN 'name_of_func1' WHEN 'func2' THEN 'name_of_func2' ... ELSE 'name_of_default_func' END

串联，而不是filter本身。

使用这种方式，使您的案例更具可读性。

Answer 2

或者您可以修改查询和一些变量以选择要运行的功能。

CREATE FUNCTION a1() RETURNS TABLE (t text, k text) AS $f$
       SELECT f1, f2 FROM t1;
$f$ LANGUAGE sql;


EXPLAIN ANALYZE
 SELECT * FROM a1() WHERE true
  UNION ALL
 SELECT * FROM a2() WHERE false
  UNION ALL
 SELECT * FROM a3() WHERE false;
                                              QUERY PLAN                                                  
--------------------------------------------------------------------------------------------------------------
 Append  (cost=0.25..20.25 rows=1000 width=64) (actual time=0.677..0.865 rows=291 loops=1)
   ->  Function Scan on a1  (cost=0.25..10.25 rows=1000 width=64) (actual time=0.676..0.758 rows=291 loops=1)
 Planning time: 0.222 ms
 Execution time: 0.981 ms

您可以一起调用所有三个功能：

EXPLAIN ANALYZE
 SELECT * FROM a1() WHERE true
  UNION ALL
 SELECT * FROM a2() WHERE true
  UNION ALL
 SELECT * FROM a3() WHERE true ;
                                              QUERY PLAN                                                  
--------------------------------------------------------------------------------------------------------------
 Append  (cost=0.25..60.75 rows=3000 width=64) (actual time=0.682..2.324 rows=873 loops=1)
   ->  Function Scan on a1  (cost=0.25..10.25 rows=1000 width=64) (actual time=0.681..0.770 rows=291 loops=1)
   ->  Function Scan on a2  (cost=0.25..10.25 rows=1000 width=64) (actual time=0.512..0.599 rows=291 loops=1)
   ->  Function Scan on a3  (cost=0.25..10.25 rows=1000 width=64) (actual time=0.557..0.644 rows=291 loops=1)
 Planning time: 0.227 ms
 Execution time: 2.615 ms

或者全部都不是

EXPLAIN ANALYZE
 SELECT * FROM a1() WHERE false
  UNION ALL
 SELECT * FROM a2() WHERE false
  UNION ALL
 SELECT * FROM a4() WHERE false ;
                                 QUERY PLAN                                      
-------------------------------------------------------------------------------------
 Result  (cost=0.00..0.00 rows=0 width=64) (actual time=0.002..0.002 rows=0 loops=1)
   One-Time Filter: false
 Planning time: 0.191 ms
 Execution time: 0.036 ms

PostgreSQL-是否可以基于过滤器运行不同的SELECT函数？

2 个答案: