mysql - if value = 0 shorten where statement - php

Question

I wonder if it's possible to shorten query depending on some variable value in elegant way.
For example: I have value named $var = 0 and I would like to send a query that looks like this:
$query = "SELECT id, name, quantity FROM products WHERE quantity > 100";
But whan the $var != 1 I'd like to send a query like this:
$query = "SELECT id, name, quantity FROM products WHERE quantity > 100 AND id = '$var'";
So depending on value of $var I want to execute one of queries. They differ only with last expression.
I found two possible solutions but they are not elegant and I dont like them at all.
One is made in php:
if ( $var == 0 ) {
$query_without_second_expression
} else {
$query_with_second_expression
}
Second is made in mysql:
SELECT WHEN '$var' <> 0 THEN id, name, quantity
FROM products WHERE quantity > 100 AND id = '$var' ELSE id, name, quantity
FROM products WHERE quantity > 100 END
but i dont like it - each idea doubles queries in some whay. Can I do something like this?
SELECT id, name, quantity
FROM products WHERE quantity > 100
CASE WHEN $var <> 0 THEN AND id = '$var'
It's much shorter, and adds part of query if needed. Of course real query is much more complicated and shorter statement would be really expected. Anyone has an idea?

Answer 1

If I understand well..
$query = "SELECT id, name, quantity FROM products WHERE quantity > 100";
if ( $var != 0 ) {
$query .= " AND id = '$var'";
}
do you like it?

Answer 2

You could so something like this on the SQL side:
"SELECT id, name, quantity FROM products WHERE quantity > 100 AND (id = '$var' OR '$var' = 0)
But performance could be impacted. I would suggest building the appropriate query on the PHP side.

Answer 3

I'm no PHP developer (it is PHP, right?), but wouldn't it be easiest to build your query from a concatenated string?
Pseudo-code:
$my_query = "SELECT id, name, quantity FROM products WHERE quantity > 100"
if ($var != 1)
$my_query = $my_query + " AND id = '$var'";
end if;
/*go ahead with your query*/

Answer 4

You can do this:
SELECT id, name, quantity
FROM products
WHERE 1 = 1
AND ( $q IS NULL OR quantity > $q)
AND ( $var IS NULL OR id = $var)
If you want only the first condition to run then pass $q = 100 and $var = NULL, therefore the second condition will be ignored. And for the second query pass the $q = 100 and $var = id value and you will got the your second query.

Answer 5

If they only differ in additional where-statements, I would probably still stay in PHP and do the following:
$conditions = array();
$conditions[] = "(quantity > 100)"
if ($var == 0)
$conditions[] = "(id = '$var')";
if (some-other-expression)
$conditions[] = "(myfield = 'foo' OR myfield = 'bar')";
$sql = "
SElECT id, name, quantity
FROM products
WHERE
";
$sql .= $conditions.join(" AND ");
/ Carsten

Answer 6

I would use a ternary for this:
$query = "SELECT id, name, quantity FROM products WHERE quantity > 100" . ( $var != 0 ? " AND id = '$var'" : '' );

Answer 7

I'm an Oracle guy, but could you use the IF() function in your constraints, e.g.:
SELECT id, name, quantity
FROM products
WHERE quantity > 100
AND id = IF('$var'=0,'%','$var');
The '%' is a wildcard that would match anything, effectively ignoring the 2nd expression.

Answer 8

So if you are using the
If or the CASE
Why don't you use them in your sql query.
It would be some like
if ( $var == 0 ) {
$query_without_second_expression
}
else
{
$query_with_second_expression
}
But in you sql query.
DECLARE #var int
if(#var=1)
BEGIN
query 1
END
else
BEGIN
query 2
end
I guess this will solve your problem.
But as a personal advice try to make one query. Even with the variable. We don't believe in changing standard query depending on the conditions.
Still your wish and your desire
Cheers!!

Answer 9

For this particular problem, go with Paper-bat's simple condition append snippet.
However, if you have entirely different where statements, consider appending the appropriate where statement to the query once you know what you want. For instance,
$query = "SELECT id, name, quantity FROM products ";
if ( $var == 0 ) {
$query .= "quantity > 100";
} elseif {
$query .= "quantity > 120 AND id = '$var'";
} elseif {
...
}
...
It all depends on your needs, but neither this or Paper-bat's solutions duplicate query code.