如何在另一个游标内声明游标答案

【问题标题】：How to declare a cursor inside another cursor如何在另一个游标内声明游标
【发布时间】：2021-08-27 06:59:14
【问题描述】：

如何在游标c_employees内声明另一个游标？

注意：游标c_employees 返回employees_id，并且此id 传递给where 子句中的其他游标。

例如

cursor c_employees
        is
            Select employees_id from employees;
begin
    for e in c_employees loop
        begin
           --How here define other cursor from cursor_employees I get employees_id and put as parameter.

           cursor c_leaves is Select hours from my_table where employees_id = e.employees_id;
           for j in c_leaves loop
                begin
                   Insert into table2(......
                end;
           end loop;

【问题讨论】：

标签： sql oracle plsql

【解决方案1】：

因此游标可以带参数

cursor c_employees    is
            Select employees_id from employees;
cursor c_leaves(e_id int)
  is Select hours from my_table where employess_id = e_id;
            
begin
    for e in c_employees loop
        begin
           for j in c_leaves(e.employees_id) loop
                begin
                   Insert into table2(......
                end;
           end loop;

但一般来说，当您开始看到带有游标等的游标时......也是时候看看是否可以用 JOIN 替换查询。例如，可能上面的代码可能只是

insert into table2
select ..
from employees e, my_table m
where e.employess_id = m.employess_id;

【讨论】：

【解决方案2】：

你需要DECLARE变量：

DECLARE
  cursor c_employees is
    Select employees_id from employees;
begin
    for e in c_employees loop
      DECLARE
        cursor c_leaves is
          Select hours from my_table where employess_id = e.employess_id;
      begin
        for j in c_leaves loop
          begin
            Insert into table2(......
          end;
        end loop;

但是，在这种情况下，您可以根据@ConnorMcDonald 的回答（还需要DECLARE 关键字）使用带有变量的光标DECLARE。

【讨论】：