光标选择语句中的变量

Question

我试图使用PLSQL获取多个表的计数，有4个表 - 测试，测试1，测试2，测试3。

表测试具有我需要的所有表的详细信息，并使用以下程序使用光标实现相同。

declare 
var varchar2(20); 
var2 varchar2(20); 
cursor C1 is select tab_name from testing; 
begin 
open C1; 
loop 
fetch C1 into var; 
exit when C1%notfound; 
select count(*) into var2 from var; 
dbms_output.put_line(var2); 
end loop; 
end; 
/

但是，得到下面的错误上执行：

select count(*) into var2 from var; 
           * 
ERROR at line 10: 
ORA-06550: line 10, column 32: 
PL/SQL: ORA-00942: table or view does not exist 
ORA-06550: line 10, column 1: 
PL/SQL: SQL Statement ignored 

Answer 1

你必须使用execute immediate与dynamic sql。

declare 
    var varchar2(50); 
    var2 number; 
    cursor C1 is select tab_name from testing; 
begin 
    open C1; 
    loop 
     fetch C1 into var; 
     exit when C1%notfound; 
     execute immediate 'select count(*) from ' || var into var2; 
     dbms_output.put_line(var2); 
    end loop; 
end; 
/

你可以使用Implicit Cursors like;

declare 
    var number; 
begin 
    for i in (select tab_name from testing) loop 
     execute immediate 'select count(*) from ' || i.tab_name into var; 
     dbms_output.put_line(var); 
    end loop; 
end; 
/

Answer 2

set serveroutput on; 
declare 
var varchar2(20); 
var2 varchar2(20); 
cursor c is select field1 from testing; 
begin 
for c1 in c 
loop 
var2:=c1.field1; 
execute immediate 'select count(*) from ' || var2 into var; 
-- below query won't work as we are creating a dynamic SQL statement 
--select count(*) into var from var2; 
dbms_output.put_line(var); 
end loop; 
end;