Note for processing NULL values in Mysql integer operations: mysqlnull

Note for processing NULL values in Mysql integer operations: mysqlnull

When CleverCode was recently exporting a report, it was found that the integer was null after the integer was subtracted. This is a matter of detail. I hope you will pay attention to it later.

Total and used values in Table 1 are all integer values, which can be null.

2. Incorrect operation statement Subtraction

select id,total,used,(total - used) as have from test_table

3. Use ifnull to handle null.

select id,ifnull(total,0) as total,ifnull(used,0) as used,(ifnull(total,0) - ifnull(used,0)) as have from test_table

4. Suggestions
1) when designing a table, if you find that this column is the column to be computed, we recommend that you set the default value, such as 0; 2) when performing an integer column operation, whether it is adding or subtracting, multiplication, division, etc. You must use ifnull to process columns. Otherwise, the report data is incorrect.
These are all minor details. You can understand them at a Glance. I hope you will pay attention to the details. Otherwise, a financial report calculation error will cause serious consequences!

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