Unknown column '? 'In' WHERE clause'

When writing PHP, there are many problems with database interaction, but the solution provided by the prompt is still very clear.

This error is caused by the SQL syntax. The statement is as follows:

Select food_num from foodlist where food_name = $ fname

The reason for this error is that the data type of food_name is varchar (255). When the varchar type is matched, It is a string. Therefore, it is not considered a string without quotation marks. Solution:

Select food_num from foodlist where food_name = '$ fname'

Similarly, statements such as update and insert must be processed in the same way.

Unknown column '? 'In' WHERE clause'