如何在SQL的WHERE子句中用通配符char替换空变量

Question

Im passing two variables, via ajax - post method, into WHERE statement in query. Second variable $var2 is optional and it may or may not be sent. That means that second variable can be empty and query would not return any result.

SELECT table1.*
        FROM table1
        LEFT OUTER JOIN table2 ON table1.table2_id = table2.id 
        WHERE table2.field1 = '".$var1."' AND table2.field2 = '".$var2."'
        ORDER BY table2.counter DESC
        LIMIT 10;

My first thought was to write if statement, something like

if(empty($var2)){
   query = ....WHERE table2.field1 = '".$var1."'...
}else{
   WHERE table2.field1 = '".$var1."' AND table2.field2 = '".$var2."'
}

Second thought was to assign * wildcard to $var2 if it is empty(this is not working).

Is there better way than if statement that could handle this problem?

Thanks

Answer 1

I usually do something like this:

$descriptiveName = !empty($var2) ? "AND table2.field2 = '$var2'" : "";

"SELECT table1.*
FROM table1
LEFT OUTER JOIN table2 ON table1.table2_id = table2.id 
WHERE table2.field1 = '$var1'
$descriptiveName
ORDER BY table2.counter DESC
LIMIT 10"

That will set the $descriptiveName variable to a blank string (that will be ignored) if $var2 is empty. It is also easy to add more than one condition this way, but if there are too many it is usually better to have two separate queries.

Answer 2

This approach is correct;

if(empty($var2)){
   query = ....WHERE table2.field1 = '".$var1."'...
}else{
   WHERE table2.field1 = '".$var1."' AND table2.field2 = '".$var2."'
}

Add or take away from the query depending on the arguments. I do not think there is a wildcard like you want. Even if there was it doesn't matter, as omitting the second statement using an if has the same effect.