Shulou(Shulou.com)06/01 Report--

Select 10 + 10 + 10 from dual

The result is 30, no problem at all.

Select null + 10 + 10 from dual

The result is an empty string, but the expected result is 20.

Select nvl (null,0) + 10 + 10 from dual

The result of this treatment is 20. If the query has a null value, it needs to be processed by nvl, otherwise the operation will be incorrect.

Select null | | 10 | | 10 from dual

There is no problem with string concatenation.

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