MySql WHERE子句是否有通配符运算符？

Question

The following MySql SELECT via PHP successfully returns rows containing a color specified by the variable $my_color .

$my_color = "red";
$a = $pdo->prepare("SELECT * FROM my_table WHERE color=:color");
$a->bindParam('color', $my_color);
$a->execute();
$data = fetchAll(PDO::FETCH_ASSOC);

I would also like to perform searches that are not dependent on specific colors. I can do this with an if-then block to use a different SELECT pattern but...

Question: Does MySQL have the ability to set a WHERE condition to something that translates to "accept anything" ( WHERE = * )?

Answer 1

You can use a LIKE clause with the input being a wildcard character like this:

$my_color = "%";
$a = $pdo->prepare("SELECT * FROM my_table WHERE color LIKE :color");
$a->bindParam('color', $my_color);
$a->execute();
$data = fetchAll(PDO::FETCH_ASSOC);

More Info on the LIKE clause

Answer 2

Use LIKE instead of = . If the value doesn't contain any wildcard characters, LIKE performs an exact equivalence check. But then you can use % as a wildcard to match anything. So:

$color = '%';
$a = $pdo->prepare("SELECT * FROM my_table WHERE color LIKE :color");
$a->bindParam('color', $my_color);
$a->execute();
$data = fetchAll(PDO::FETCH_ASSOC);

However, a better option might be to put the logic in PHP rather than SQL.

if ($color) {
    $a = $pdo->prepare("SELECT * FROM my_table WHERE color=:color");
    $a->bindParam('color', $my_color);
} else {
    $a = $pdo->prepare("SELECT * FROM my_table");
}
$a->execute();

See https://stackoverflow.com/a/28909923/1491895 for a more general technique for building the WHERE clause dynamically from multiple form inputs.