oracle循环排序

Question

我有 pl/sql 的循环脚本，我的脚本按 i asc 返回顺序，

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;

它返回了

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 return 你想要什么：

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;

不过，那只是因为数据量小。 Oracle 不保证没有 ORDER BY 的结果集的顺序。所以比较安全的方法是：

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 return 排序不同 结果。另一方面 UNION ALL 运算符 return 重复未排序 结果

试试下面的查询：- 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

As 索引的主要起始参考点可能是 i-1 中的 sql 语句的一部分。

因此，以下光标可能是首选：

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

oracle loop ordering

sql

oracle

sql-order-by

oracle11g