Problems related to the return value of PDO: exec ()

PDO: exec () returned value. // Set the script running time to set_time_limit (0); // use PDO to create a pgsql connection try {$ pgLink = newPDO ('pgsql: host = localhostport = 5432 dbname = db2user = root PDO: exec () returned value.
// Set the script running time to unlimited
Set_time_limit (0 );

// Use PDO to create a pgsql connection
Try {
$ PgLink = new PDO ('pgsql: host = localhost port = 5432 dbname = db2 user = root password = 661 ');
} Catch (Exception $ e ){
Echo $ e-> getMessage ();
}

// Define the SQL modification statement
$ SQL = "UPDATE trade. membership SET gender = 1, birth_type = 0, name = 'wsy', birthday = '2017-01-01 ', email = '', join_date = '2017-01-02 ', status = 1, address = 'AAA', id_number = '000000', postcode = '000000', phone = '000000', type_id = 1 WHERE mobile = '000000 ';";

// Execute the SQL statement
$ Result = $ pgLink-> exec ($ SQL );

// Output SQL results
Echo $ result. ''. $ SQL;

Output result:
1 UPDATE trade. membership SET gender = 1, birth_type = 0, name = 'wsy', birthday = '2017-01-01 ', email = '', join_date = '2017-01-02 ', status = 1, address = 'AAA', id_number = '000000', postcode = '000000', phone = '000000', type_id = 1 WHERE mobile = '000000 ';

The problem is as follows:
There is no row of mobile = '000000' in this table at all. getting the $ SQL statement to the local SQL server is also "0 affected rows ".
But why is the result in the program "1 "? Shouldn't the output result of PDO: exec () be the number of affected rows added, deleted, and modified?

------ Solution --------------------
This should be a pdo bug, which can be correctly handled by preprocessing and then using PDO: rowCount.