When assigning to a single object, a query that returns anything other than a single row will throw a QueryException
.
try {
Account a = [SELECT Id FROM Account WHERE Name = 'Non-existent Account'];
} catch (QueryException e) {
// List has no rows for assignment to SObject
}
try {
Account a = [SELECT Id FROM Account];
} catch (QueryException e) {
// List has more than 1 row for assignment to SObject
}
Attempting to use a field that you did not include in the query will throw a SObjectException
Account a = [SELECT Id FROM Account LIMIT 1];
try {
System.debug( a.Name );
} catch (SObjectException e) {
// SObject row was retrieved via SOQL without querying the requested field: Name
}