Question

I’m using php + mysql, I have such table in DB:

col1-col2-col3
A - val1 - str1
A - val2 - str2
A - val3 - str3
B - val4 - str4
B - val5 - str5
...

And also assoc array in php:

$arr = array('A'=>'value1','B'=>'value2', ...);

Then I’m passing this array in placeholders in MySql string to make complete SELECT statement.

How to choose column 3 values where value of column 1 equals to key of array AND column 2 values are less than array value respectively? Maybe using somehow GROUP with two selects and joining them together…

The result should be just list of all column 3 values that satisfied requirements.

It can be done using sth like this:

$aReturn = array();
$sql = "SELECT col3 FROM MyTab WHERE col1 = ? AND col2 < ?d";
foreach ($arr as $k=>$v) {
    $aReturn = array_merge($aReturn, $this->select($sql, $k, $v));
}

Where select is method which makes select to DB and returns values of last column in list of values, then we add list to result $aReturn. But in this case it will query several times,
but is there a way how to do it in only one SELECT?

Answer 1

I don’t think this can be done with placeholders, because the structure of the query isn’t fixed — you need as many conditions in the WHERE clause as you have elements in the array. Here’s untested code:

UPDATED: uses prepared statement

$wheres = array();
$types = '';
$col1s = array();
$params = array(null, null);
$i = 0;
foreach ($assoc as $key => $val) {
  $wheres[] = '(col1 = ? AND col2 < ?)';
  $types .= 'ss';
  $col1s[$i] = $key;
  $params[] = &$col1s[$i];
  $params[] = &$assoc[$key];
  $i++;
}
$whereclause = implode(' OR ', $wheres);
$sql = "SELECT * FROM my_table WHERE $whereclause";
$stmt = mysqli_prepare($link, $sql);
$params[0] = $stmt;
$params[1] = $types;
call_user_func_array('mysqli_stmt_bind_params', $params);
mysqli_stmt_execute($stmt);