Hedi Hadhri's questions

我编写了以下函数来从我作为参数提供的表和列中查询数据：

create or replace function field_summaries(gap interval , _tbl anyelement, _col text)                                
 returns SETOF anyelement as 
 $func$   
 BEGIN
 RETURN QUERY EXECUTE
 'select                                                                                                                       
 time_bucket(' || gap || ', time)::text as hour,                                                                                      
 avg(' || _col ||'),                                                                                                          
 min(' || _col ||'),                                                                                                          
 max(' || _col ||')                                                                                                         
 from ' || pg_typeof(_tbl) || ' d                                                                                                         
 where d.device_id in (                                                                                                       
     select device_id from sensors)                                                                                           
     group by hour';
 END
 $func$ language sql stable;  

问题是当调用这样的函数时：

select field_summaries('5minutes', NULL:: m_13, 'temperature');   

我收到以下错误：

ERROR:  syntax error at or near ":"  
LINE 2:  time_bucket(00:05:00, time)::text as hour,                 ...                                                                           
                       ^                                                                                                   
QUERY:  select                                                                                                                                                                                                                                         
time_bucket(00:05:00, time)::text as hour,                                                                                                                                                                                                            
avg(temperature),                                                                                                                                                                                                                                     
min(temperature),                                                                                                                                                                                                                                     
max(temperature)                                                                                                           
from m_13 d                                                                                                                
where d.device_id in (                                                                                                                                                                                                                                    
select device_id from sensors)                                                                                                                                                                                                                        
group by hour                                                                                                         
CONTEXT:  PL/pgSQL function field_summaries(interval,anyelement,text) line 3 at RETURN QUERY

有谁知道这可能是什么？