数据库新手 - Oracle

Question

我对 Oracle 和数据库还很陌生。

我正在尝试使用游标编写存储过程。如何在游标循环内编写 select 语句，以及如何遍历从该游标循环内的 select 获得的结果集？

例如：

    Open Curs1;
    Exit When Curs1%NotFound;
    Loop
       Select column1,column2  from table -- Returns multiple records. How to loop through this record set and perform CRUD operations.
    End loop;
    Close Curs1;

Answer 1

使用 FOR 循环游标 - 它们比打开/获取/关闭语法更快、更简单。

begin
    for results1 in
    (
        select ...
    ) loop
        --Do something here
        for results2 in
        (
            select ...
            where some_table.some_column = results1.some_column
        ) loop
            --Do something here
        end loop;
    end loop;
end;
/

虽然这从字面上回答了这个问题，但您通常不希望在这样的循环内有循环。如果可能的话，最好将两个 SQL 语句用一个连接组合起来，然后循环遍历结果。

Answer 2

尝试使用以下示例，从游标变量 emp_cv 一次获取一行到用户定义的记录 emp_rec：

declare
   TYPE YourType IS ref cursor return YourTable%rowtype;
   tab_cv  YourType;
   tab_rec YourTable%rowtype;
begin
   loop
      fetch tab_cv into emp_rec;
      exit when tab_cv%notfound;
      ...
   end loop;
end;

BULK COLLECT 子句允许您从结果集中获取整个列，或一次获取整个结果集中。以下示例从游标中检索列到集合中：

declare
   type NameList IS table of emp.ename%type;
   names NameList;
   cursor c1 is select ename from emp where job = 'CLERK';
begin
   open c1;
   fetch c1 bulk collect into names;
   ...
   close c1;
end;

以下示例使用 LIMIT 子句。在循环的每次迭代中，FETCH 语句将 100 行（或更少）提取到按索引表 acct_ids 中。之前的值会被覆盖。

declare
   type NumList is table of number index by binary_integer;
   cursor c1 is select acct_id from accounts;
   acct_ids NumList;
   rows natural := 100;  -- set limit
begin
   open c1;
   loop
      /* The following statement fetches 100 rows (or less). */
      fetch c1 bulk collect into acct_ids limit rows;
      exit when c1%notfound;
      ...
   end loop;
   close c1;
end;

Answer 3

您需要在循环中声明CURSOR 和FETCH 记录。

DECLARE
CURSOR  curs1
IS
  SELECT column1,
         column2
  FROM   yourtable;

  v_column1 yourtable.column1%TYPE;
  v_column2 yourtable.column2%TYPE;
BEGIN
 OPEN curs1;
  LOOP

    FETCH curs1
    INTO  v_column1,
          v_column2;
  EXIT
  WHEN curs1%NOTFOUND;

    INSERT INTO yourtable2(col1)VALUES( '000'||v_column1  ); 
    -- A sample DML operation.

    --Do other operations on individual records here.
  END LOOP;
  CLOSE curs1; 
END;