为什么这个mysql查询不起作用？

Question

I have this query:

$q = $dbc -> prepare("SELECT * FROM mailbox WHERE msgTo = ? && read = 0");
$q -> execute(array($user['id']));
$mailboxCount = $q -> rowCount();

Now in my table I have

msgTo = 1, read = 0

$user['id'] is equal to 1

But the row count returns 0 why is this?

Answer 1

from Manual

PDOStatement->rowCount — Returns the number of rows affected by the last SQL statement

PDOStatement::rowCount() returns the number of rows affected by the last DELETE, INSERT, or UPDATE statement executed by the corresponding PDOStatement object.

SEE this example and written clearly

For most databases, PDOStatement::rowCount() does not return the number of rows affected by a SELECT statement. Instead, use PDO::query() to issue a SELECT COUNT(*) statement with the same predicates as your intended SELECT statement, then use PDOStatement::fetchColumn() to retrieve the number of rows that will be returned.

Answer 2

IMHO rowCount() only matches on UPDATE and DELETE statements and not on SELECT queries. By selecting * you fetch all data from the database. Since you only want the number of rows, use the count()-function instead - that is much more efficient.

SELECT count(*) FROM mailbox WHERE msgTo = ? && read = 0