Effect of null value in mysql on expression Calculation

The impact of null value in mysql during expression computation in mysql when any type of field and null value are calculated, the result is still null value www.2cto.com For example, 1 + null = null 'A' + null = null sometimes the null value must be automatically converted to an integer for expression calculation. use the CONVERT and CAST functions to forcibly CONVERT null to an integer type .. failed. finally, the if statement is used to solve this problem. For example, if (a is null, B, B + a) as c indicates that when field a is null, only calculate the value of field B and use the alias c. Otherwise, add the value of field B and field a to obtain the alias c a B null 1 1 1 select if (a is null, B, B + a) as c from table, the final result is c 1 2.