The Oracle database fuzzy query statement is a result that is easy to ignore: Empty records

Cause:

The SQL statement is as follows:

Select count (*) from test;

Result 1390.

Select count (*) from test where BB not like '% disable %'

Result 393.

In the actual browsing process, it is found that the result set is not disabled and there are certainly more than 393 records.

Process:

1. First, we suspect that the character set of the client does not match the server character set.

After the preceding SQL statement is used on another machine, the results are the same.

2. I still suspect that it is a character set problem. I have not found the real cause of the problem, and almost went crazy.

3. I accidentally found that many BB fields are empty. After careful analysis, I found that bb not like '% disabled %' does not match null records, so I changed it

Select count (*) from test where BB not like '% disable %' or BB is null

The result is 1356.

Conclusion:

Fuzzy match is not often used, so it will lead to careless use, and eventually lead to human madness.