在PL/SQL的检索语句中，为何出现了相同的表名而进行检索呢？

Question

没问题
受注明細情報 OY,受注明細情報 KO
这是自连接的一种方式

Answer 1

1.尽量不要使用中文命名栏位
2.同样的表名是可以理解的,一般都是用来做自连接或本表数据的有条件计算
for example:
SQL> select * from test_tab;COL_A           COL_B COL_C
---------- ---------- --------------------
A                   1 
A                   2 
B                   2 
B                   3 
C                   4 
D                   1 
D                  12 
D                 121 
D                  12 9 rows selected----下面同时显示2次表TEST_TAB
SQL> select * from test_tab a,test_tab b
  2  where a.col_a = b.col_a
  3  and  a.col_b = b.col_b
  4  /COL_A           COL_B COL_C                COL_A           COL_B COL_C
---------- ---------- -------------------- ---------- ---------- --------------------
A                   1                      A                   1 
A                   2                      A                   2 
B                   2                      B                   2 
B                   3                      B                   3 
C                   4                      C                   4 
D                   1                      D                   1 
D                  12                      D                  12 
D                  12                      D                  12 
D                  12                      D                  12 
D                  12                      D                  12 
D                 121                      D                 121 11 rows selected
----下面计算TEST_TAB的COL_B的相加数(其实这里没有必要做的这么麻烦只是用来做演示:)SQL> select a.col_a,a.col_b+b.col_b sum_num from test_tab a,test_tab b
  2  where a.col_a = b.col_a and  a.col_b = b.col_b
  3  /COL_A         SUM_NUM
---------- ----------
A                   2
A                   4
B                   4
B                   6
C                   8
D                   2
D                  24
D                  24
D                  24
D                  24
D                 24211 rows selected