How to search for information based on qualification criteria

It turns out that all the rows in the database are displayed
There are several options in the drop-down box, I choose Beijing, then click Submit, on the same page will be all places are Beijing's row show, ask how to write
How to write if there are several qualifications at the same time.
If the option is empty, it will not be added to the qualifying conditions.

Reply to discussion (solution)

The front end takes the data such as location = ' Beijing ' Post in the past, the backend receives the data, adds the Where condition on the original SQL statement, the condition is the place = ' Beijing ' and so on.

By default, the values of filter conditions such as locations are passed empty
Get all the data in the background

If location = ' Beijing ', SQL takes Beijing related data, other conditions and so on, long term combination

By default, the values of filter conditions such as locations are passed empty
Get all the data in the background

If location = ' Beijing ', SQL takes Beijing related data, other conditions and so on, long term combination

What data will not be displayed if the transfer is just started?

The front end takes the data such as location = ' Beijing ' Post in the past, the backend receives the data, adds the Where condition on the original SQL statement, the condition is the place = ' Beijing ' and so on.

What if you want to work on the same page?

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