使用lateral join代替：

select e.errordescription, ge.name
from error_log_gs e left join lateral
     get_empname(e.reworkempid) ge(name)
     on e.reworkempid is not null
where e.qcworkpackageid = 3012175 and e.logno = 1 ;

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我遇到的确切错误是，0A000：在CASE中不允许设置返回函数。
在调查时，发现该语法在Postgres 9.6版中有效，但在11版中无效。
为了克服这个问题，我又添加了一个CTE（公共表表达式），如下所示，解决了我的问题。

cte as  
( 
select string_to_array("StartDate", ',') as "S1_StartDate", 
       string_to_array("EndDate", ',') as "S1_EndDate", 
       case  when "FlatDisc" is  null then '{0}' when "FlatDisc" ='' then '{0}' else string_to_array("FlatDisc", ',') end as "S1_FlatDisc" 
       from TABLE_XYZ 
) 
,cte2 as 
( 
select unnest("S1_StartDate") as "S_StartDate", 
       unnest("S1_EndDate") as "S_EndDate", 
       unnest("S1_FlatDisc") as "S_FlatDisc" 
       from cte 
)
select * from cte2

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