有没有办法搜索mySQL数据库中的所有表？

Question

Basically I have a database full of tables and I want to go through them all until I find a result that matches my search query. Is there a way to do this? Or at least a command to return all of the table names so that I could loop through them until I find the right value?

thanks!

Answer 1

Aaah, search engines. Exciting subject, but I would rather build something with internal intelligence rather than using brute force solution. Yes - checking every table/column in database is brute force and may result in sluggishness and false positives.

Let me present you with something I would use instead. With below solution each table/column worth scanning needs to be added manually, but everything else is automatic. Here's the usage:

$e = new SearchEngine();
$e->addTable('users', 'id', 'login'); // table, primary key name, column to be searched in
$e->addTable('users', 'id', 'last_name');
$e->addTable('towns', 'id', 'name');

print_r($e->search('austin')); // we search for exact match for word "austin"

And here's how it was implemented:

class SearchEngine {

    protected $tables = array();

    public function addTable($table, $key, $column) {
        $this->tables[] = array(
            'table' => $table,
            'key' => $key,
            'column' => $column
        );
    }

    public function search($term) {
        $q = array();
        foreach ($this->tables as $t) {
            list($table, $key, $column) = $t;
            $q[] = "
                SELECT
                    $key AS searched_key,
                    '$key' AS searched_key_name,
                    '$table' AS searched_table,
                    '$column' AS searched_column,
                    $column AS searched_value
                FROM $table
                WHERE $column = $term
            ";
        }
        $sql = implode(' UNION ', $q);
        // query the database
        // return results
    }

} // class SearchEngine

Let's analyse example output:

searched_key | searched_key_name | searched_table | searched_column | searched_value
-------------+-------------------+----------------+-----------------+---------------
         276 |                id | users          | login           | austin
        1782 |                id | users          | last_name       | austin
          71 |                id | towns          | name            | austin

From the table above you can figure out that phrase "austin" was found in table users, column login (primary key 276) and column last_name (primary key 1782). It was also found in table towns in column name (primary key 71);

Such search result may be sufficient for you. Or else, you can further process the list to select full row from each table:

$out = array();
foreach ($rows as $row) {
    $sql = "
        SELECT * FROM {$row['searched_table']}
        WHERE {$row['searched_key_name']} = {$row['searched_key']}
        LIMIT 1
    ";
    // query the database
    // append result to $out array
}
return $out;

This way you will end up with full search result (as opposed to intermediate results from previous table):

id: 276, login: austin, last_name: Powers, email: [e-mail]
id: 1782, login: michael, last_name: austin, email: [e-mail]
id: 71, name: austin, state: texas, country: usa

Because current implementation is restricted to fixed comparison operator (WHERE field = value), you may want to introduce some flexibility here. If so, search operator needs to be delegated to external class and injected into search() function:

public function search(SearchOperator $operator, $term) {
...

Then SearchOperator needs to be taken into account by replacing WHERE condition with the below:

WHERE {$operator->toSQL($column, $term)}

Now let's focus on SearchOperator implementation. Since operator implementation provides only one method, namely toSQL, we don't need full class, or even abstract class. Interface will suffice in this case:

interface SearchOperator {

    public function toSQL($column, $term);

} // interface SearchOperator

And let's define couple of implementations representing = (equals) and LIKE operators:

class Equals implements SearchOperator {

    public function toSQL($column, $term) {
        return "$column = '$term'";
    }

} // class Equals

class Like implements SearchOperator {

    public function toSQL($column, $term) {
        return "$column LIKE '$term'";
    }

} // class Like

Naturally, any other implementation is possible - think about classes called StartsWith, EndsWith, or DoesNotContain.

See updated solution usage:

$e = new SearchEngine();
$e->addTable('users', 'id', 'login');
$e->addTable('users', 'id', 'last_name');
$e->addTable('towns', 'id', 'name');

print_r($e->search(new Like(), 'austin%')); // here we search for columns being LIKE 'austin%'

Time to leave some final remarks:

• Above examples are incomplete. Database querying code was omitted for clarity.
• SQL used in examples does not sanitize input data. I strongly urge you to use prepared statements with bound parameters to avoid huge security risk.
• Search algorithm presented above is a naive one. Some optimisation can be done (i.e. grouping queries referring to the same table). But don't optimise prematurely - wait until it becomes a real issue.

Hoping this was helpful.