"pdo::exec or pdo::execute?" Code Answer

although both methods have a similar naming (exec,execute) they're meant to be used in different scenarios:

1. exec is used to get the number of affected rows.

   /**
    * (php 5 &gt;= 5.1.0, pecl pdo &gt;= 0.1.0)<br/>
    * execute an sql statement and return the number of affected rows
    * @link http://php.net/manual/en/pdo.exec.php
    * @param string $statement <p>
    * the sql statement to prepare and execute.
    * </p>
    * <p>
    * data inside the query should be properly escaped.
    * </p>
    * @return int <b>pdo::exec</b> returns the number of rows that were modified
    * or deleted by the sql statement you issued. if no rows were affected,
    * <b>pdo::exec</b> returns 0.
    * </p>
    * this function may
    * return boolean <b>false</b>, but may also return a non-boolean value which
    * evaluates to <b>false</b>. please read the section on booleans for more
    * information. use the ===
    * operator for testing the return value of this
    * function.
    * <p>
    * the following example incorrectly relies on the return value of
    * <b>pdo::exec</b>, wherein a statement that affected 0 rows
    * results in a call to <b>die</b>:
    * <code>
    * $db->exec() or die(print_r($db->errorinfo(), true));
    * </code>
    */
   public function exec ($statement) {}
   

   example:

   $myquery = "update users set email = 'testing'";
   $affectedrows = $db->exec($myquery);
   

2. execute is used when you want to pass an array of parameters to be bind in the query.

   /**
    * (php 5 &gt;= 5.1.0, pecl pdo &gt;= 0.1.0)<br/>
    * executes a prepared statement
    * @link http://php.net/manual/en/pdostatement.execute.php
    * @param array $input_parameters [optional] <p>
    * an array of values with as many elements as there are bound
    * parameters in the sql statement being executed.
    * all values are treated as <b>pdo::param_str</b>.
    * </p>
    * <p>
    * you cannot bind multiple values to a single parameter; for example,
    * you cannot bind two values to a single named parameter in an in()
    * clause.
    * </p>
    * <p>
    * you cannot bind more values than specified; if more keys exist in
    * <i>input_parameters</i> than in the sql specified
    * in the <b>pdo::prepare</b>, then the statement will
    * fail and an error is emitted.
    * </p>
    * @return bool <b>true</b> on success or <b>false</b> on failure.
    */
   public function execute (array $input_parameters = null) {}
   

   example (of course this might be an update or delete query as well):

   $myquery = 'select * from users where username = :username';
   $params = array(':username' => 'admin');
   $db->query($myquery)->execute($params);
   

3. query returns a pdostatement object

   /**
    * (php 5 &gt;= 5.1.0, pecl pdo &gt;= 0.2.0)<br/>
    * executes an sql statement, returning a result set as a pdostatement object
    * @link http://php.net/manual/en/pdo.query.php
    * @param string $statement <p>
    * the sql statement to prepare and execute.
    * </p>
    * <p>
    * data inside the query should be properly escaped.
    * </p>
    * @return pdostatement <b>pdo::query</b> returns a pdostatement object, or <b>false</b>
    * on failure.
    */
   public function query ($statement) {}
   

for more information you can visit the php docs or in case you're using phpstorm you can go though the source code of the pdo.php class.