这是对上一个问题的跟进:Dynamicly build select statement in Oracle 12c
我正在尝试动态构建 select 语句,但在构建列别名时遇到问题。必须从 MAIN_TABLE 中检索列别名。请参考下面<>里面的代码:
declare
upper_level number;
t_sql varchar2(1000);
t_sql_val varchar2(500);
l_sql varchar2(1000);
begin
--upper_level will always be given
select 3 into upper_level from dual;
--build the fixed string
l_sql:='SELECT ID,
Title,
Desc,
Type,';
for lvl in 1..upper_level
loop
--build the column names and alias names
t_sql:=t_sql||'TYPE_'||lvl||' <SELECT TYPE_'||lvl||' FROM MAIN_TABLE WHERE ID = 1>,';
end loop;
--finish building the statement
t_sql:=rtrim(t_sql,',');
l_sql:=l_sql||t_sql;
l_sql:=l_sql||' FROM SCHEMA.TABLE
WHERE ID = 1;';
--dbms_output.put_line(l_sql);
end;
这是我的尝试:
declare
upper_level number;
t_sql varchar2(1000);
v_sql varchar2(1000);
v_sql_val varchar2(1000);
t_sql_val varchar2(500);
l_sql varchar2(1000);
begin
--upper_level will always be given
select 3 into upper_level from dual;
--build the fixed string
l_sql:='SELECT ID,
Title,
Desc,
Type,';
for lvl in 1..upper_level
loop
--build the column names and alias names
t_sql:='TYPE_'||lvl||;
v_sql:='SELECT '||t_sql||' FROM MAIN_TABLE WHERE ID=1';
EXECUTE IMMEDIATE v_sql into v_sql_val;
t_sql:=t_sql||' '||v_sql_val||',';
end loop;
--finish building the statement
t_sql:=rtrim(t_sql,',');
l_sql:=l_sql||t_sql;
l_sql:=l_sql||' FROM SCHEMA.TABLE
WHERE ID = 1;';
dbms_output.put_line(l_sql);
end;
我的尝试结果:
SELECT ID,
Title,
Desc,
Type,TYPE_3 LVL_3 FROM SCHEMA.TABLE
WHERE ID = 1;
我的预期结果:
SELECT ID,
Title,
Desc,
Type,TYPE_1 LVL_1, TYPE_2 LVL_2, TYPE_3 LVL_3 FROM SCHEMA.TABLE
WHERE ID = 1;
我怎样才能做到这一点?