Question

我有pl / sql的循环脚本，我的脚本由i asc返回，

DECLARE 
    i NUMBER;
BEGIN
    FOR rec IN (
        SELECT 1 as i from dual
        UNION
        SELECT 2 as i from dual
        UNION
        SELECT 3 as i from dual
        UNION
        SELECT 4 as i from dual
    )
    LOOP
        DBMS_OUTPUT.PUT_LINE (rec.i); 
    END LOOP; 
end;

然后它返回

但我需要订购

我应该用什么功能来解决问题，谢谢advence

Answer 1

我希望这可以归还你想要的东西：

DECLARE 
    i NUMBER;
BEGIN
    FOR rec IN (
        SELECT 1 as i from dual
        UNION ALL
        SELECT 4 as i from dual
        UNION ALL
        SELECT 3 as i from dual
        UNION ALL
        SELECT 2 as i from dual
     ) LOOP
        DBMS_OUTPUT.PUT_LINE (rec.i); 
    END LOOP; 
end;

然而，这仅仅是因为数据很小。 Oracle不保证在没有ORDER BY的情况下对结果集进行排序。所以更安全的方法是：

DECLARE 
    i NUMBER;
BEGIN
    FOR rec IN (
        SELECT i
        FROM (SELECT 1 as i, 1 as ord from dual UNION ALL
              SELECT 4 as i, 2 from dual UNION ALL
              SELECT 3 as i, 3 from dual UNION ALL
              SELECT 2 as i, 4 from dual
             ) x
        ORDER BY ord
     ) LOOP
        DBMS_OUTPUT.PUT_LINE (rec.i); 
    END LOOP; 
end;

Answer 2

而不是使用 UNION 运算符使用 UNION ALL 运算符，因为 UNION 运算符返回已排序的结果。另一方面， UNION ALL 运算符返回重复未排序结果

尝试以下查询： - SET SERVEROUTPUT ON; DECLARE i NUMBER; BEGIN FOR rec IN ( SELECT 1 as i from dual UNION ALL SELECT 4 as i from dual UNION ALL SELECT 3 as i from dual UNION ALL SELECT 2 as i from dual ) LOOP DBMS_OUTPUT.PUT_LINE (rec.i); END LOOP; end; /

Answer 3

由于sql语句的一部分，索引的主要起始参考点可能是i-1。

因此，可能会选择以下光标：

SELECT * FROM
(
 SELECT 1 as i from dual
 UNION
 SELECT 2 as i from dual
 UNION
 SELECT 3 as i from dual
 UNION
 SELECT 4 as i from dual
)
ORDER BY sign(i-1), (i-1) desc;

SQL Fiddle Demo

oracle循环排序

3 个答案: