Question

我有一个参数的以下功能。我需要显示一个包含select语句和where条件的字符串。

示例：

create or replace function funct(a int)
returns void as
$$
declare
       wrclause varchar := '';
       sqlq varchar ;
       t varchar;
begin
       wrclause := ' AND C IN ('|| a || ')';

       sqlq := ' t :=select string_agg(''select *, abcd as "D" from '' || table_namess  ||, '' Union all '') as namess
        from tablescollection2 ud
        inner join INFORMATION_SCHEMA.Tables so on ud.table_namess = so.Table_name where C = '|| a ||'' || wrclause;

       raise info '%',sqlq;

       perform sqlq;

       raise info '%',t;
end;
$$
language plpgsql;

调用函数：值为1

select funct(1);

输出：

INFO:   t :=select string_agg('select *, abcd as "D" from ' || table_namess ||, ' Union all ') as namess
        from tablescollection2 ud
        inner join INFORMATION_SCHEMA.Tables so on ud.table_namess = so.Table_name where C = 1 AND C IN (1)
INFO:  <NULL>

调用函数：使用空值

select funct(null);

输出：

INFO:  <NULL>
INFO:  <NULL>

注意：在将空字符串分配给wrclause变量之后，我没有收到为什么我收到<NULL>字符串，<NULL>为变量t }。

Answer 1

如果满足所有符合NULL的要求，您可以尝试下面的内容：

create or replace function funct(a int)
returns void as
$$
declare
       wrclause varchar := '';
       sqlq varchar ;
       t varchar;
begin
    IF (a IS NOT NULL ) THEN 
        wrclause := 'where C = '|| a ||' AND C IN ('|| a || ')';
    END IF;


       sqlq := ' t :=select string_agg(''select *, abcd as "D" from '' || table_namess  ||, '' Union all '') as namess
        from tablescollection2 ud
        inner join INFORMATION_SCHEMA.Tables so on ud.table_namess = so.Table_name ' || wrclause;

       raise info '%',sqlq;

       perform sqlq;

       raise info '%',t;
end;
$$
language plpgsql;

select funct(1);

输出：

INFO:   t :=select string_agg('select *, abcd as "D" from ' || table_namess  ||, ' Union all ') as namess
        from tablescollection2 ud
        inner join INFORMATION_SCHEMA.Tables so on ud.table_namess = so.Table_name where C = 1 AND C IN (1)
INFO:  <NULL>

select funct(null)

INFO:   t :=select string_agg('select *, abcd as "D" from ' || table_namess  ||, ' Union all ') as namess
        from tablescollection2 ud
        inner join INFORMATION_SCHEMA.Tables so on ud.table_namess = so.Table_name
INFO:  <NULL>

PostgreSQL：通过将null值传递给函数</null>来获取<null>字符串

1 个答案: