问防止向数据库插入重叠时间戳范围

EN

name            startTime               endTime
---------|------------------------|----------------------
tommy    |   2019-07-10 08:30:00  |   2019-07-10 10:30:00
tommy    |   2019-07-10 10:31:00  |   2019-07-10 11:30:00  
tommy    |   2019-07-10 07:30:00  |   2019-07-10 09:00:00 <=== if I click enter to enter this tird schedulle for this user, the sistem will give me a conflict message because this user already has a schedulle that start from 2019-07-10 08:30:00 to 2019-07-10 10:30:00 on our first row of the table.

$sql = "insert into horarios (name, startTime, endTime) values ('$name', '$startTime', '$endTime');";
$res = @pg_query ($con, $sql);
if ($res == NULL){
    echo "Query failed.";
    exit (0);
}