如何减少为此工作所需的 SQL 查询的数量？

Question

So.. I know a little bit of programming but my skills are limited. Today I'm trying to make a simple query to get the health personal working at the hospital I currently work in between the dates I choose.

I want to have 4 input dates like

Its in spanish so here is the traduction:

The date inputs are "filters"

Started working >= to this date
Started working <= to this date
Quit the job >= to this date
Quit the job <= to this date

And the 2 selects inputs are the title and specialization degree that personal have. (I need the option that both can be null)

So I can work around this making an SQL query for every possible case like this:

    if ($titulo == '0' && $especialidad == '0' && $date1!=null && $date2==null && 
$bdesde==null && $bhasta==null){     

$sql_query= "select * from personal where starting_date >= '$date1'" }
    
elseif ( ... and so on  

The database is MySQL.

But I was wondering if there is a way to do what I want with less code.

Answer 1

You could use case expressions and conditional logic:

select * 
from personal 
where 
    (:starting_date_after      is null or starting_date >= :starting_date_after)
    and (:starting_date_before is null or starting_date <= :starting_date_before)
    and (:ending_date_after    is null or ending_date   >= :ending_date_after)
    and (:ending_date_before   is null or ending_date   <= :ending_date_before)

This assumes that your query accepts 4 parameters, which may be null (ie not provided by the user) or set (ie given by the user): parameters :starting_date_after and :starting_date_before are meant to filter table column starting_date , while :ending_date_after and :ending_date_before apply to ending_date .

Note that you should be using parameterized queries (as shown above) rather than concatenating variables in the query string, to make your code more efficient, and, more importantly, to prevent SQL injection.