ORACLE，忽略null求和

Question

我想将一行的两列（数字类型）加在一起，但是当其中一列为空时，结果为空。我通过 NVL 函数 (NVL(col1,0) + NVL(col2,0)) 处理了它。但是当两者都为空（而不是 0）时，我想 return 为空。我该如何处理？ ORACLE中有忽略空值求和一行两列的函数吗？

| col1 | col2  |                                     |
|:---- |:-----:|:-----------------------------------:|
|  1   |   2   |      --> result have to be : 3      |
|  1   |  null |     --> result have to be : 1       |
| null |  null |     --> result have to be : null    |

Answer 1

CASE 表达式可能是最简单的方法：

SELECT CASE WHEN col1 IS NULL AND col2 IS NULL
            THEN NULL
            ELSE NVL(col1, 0) + NVL(col2, 0) END AS output
FROM yourTable;

Answer 2

coalesce(col1+col2,col1,col2) 会更容易：

with t(col1,col2) as (
  select 0,1 from dual union all
  select 2,null from dual union all
  select null,3 from dual union all
  select null,null from dual
  )
select 
  col1,col2,
  coalesce(col1+col2,col1,col2) sum_cols  
from t;

结果：

      COL1       COL2   SUM_COLS
---------- ---------- ----------
         0          1          1
         2       null          2
      null          3          3
      null       null       null

4 rows selected.

如果要求和的列更多，则使用求和子查询：

(select sum(column_value) from table(sys.odcinumberlist(col1,col2,...,colN)))

示例：

with t(col1,col2) as (
  select 0,1 from dual union all
  select 2,null from dual union all
  select null,3 from dual union all
  select null,null from dual
  )
select 
  col1,col2,
  coalesce(col1+col2,col1,col2) sum_cols,
  (select sum(column_value) from table(sys.odcinumberlist(col1,col2))) sum_cols2
from t;

DBFiddle: https://dbfiddle.uk/?rdbms=oracle_18&fiddle=eda8de9746f1d0def3c290420adbb705

ORACLE，忽略null求和

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