使用表的当前值更新语句

Question

我想通过将一个字段的整数值递增1来更新表中的行。

当前不起作用，为什么？

Update htmIndex SET numObs = numObs+1 where ...

Answer 1

简单案例，更新一行：

SQL> select name
  2         , age
  3  from t23
  4  where id = 2
  5  /

NAME                AGE
------------ ----------
MR KNOX              47

SQL> update t23
  2  set age = age + 6
  3  where id = 2
  4  /

1 row updated.

SQL> select name
  2         , age
  3  from t23
  4  where id = 2
  5  /

NAME                AGE
------------ ----------
MR KNOX              53

SQL>

当列具有空值时更新行：

SQL> select name
  2         , age
  3  from t23
  4  where id = 6
  5  /

NAME                AGE
------------ ----------
SALLY

SQL> update t23
  2  set age=age+5
  3  where id = 6
  4  /

1 row updated.

SQL> select name
  2         , age
  3  from t23
  4  where id = 6
  5  /

NAME                AGE
------------ ----------
SALLY

SQL> update t23
  2  set age = nvl(age,0) +5
  3  where id = 6
  4  /

1 row updated.

SQL> select name
  2         , age
  3  from t23
  4  where id = 6
  5  /

NAME                AGE
------------ ----------
SALLY                 5

SQL>

更新多行时同样直截了当：

 SQL> select name
   2         , age
   3  from t23
   4  where age > 20
   5  /

 NAME                AGE
 ------------ ----------
 MR KNOX              53
 FOX IN SOCKS         37
 CAT                  23
 LORAX               443

 SQL> update t23
   2  set age = age + 1
   3  where age > 20
   4  /

 4 rows updated.

 SQL> select name
   2         , age
   3  from t23
   4  where age > 20
   5  /

 NAME                AGE
 ------------ ----------
 MR KNOX              54
 FOX IN SOCKS         38
 CAT                  24
 LORAX               444

SQL>

Answer 2

它应该工作。但是，如果当前列值为null，则+ 1将返回null。

尝试：Update htmIndex SET numObs = nvl(numObs,0)+1 where ...