I have a text column that contains JSON and also plan text. I want to convert it to JSON, and then select a particular property. For example:

```
user_data
_________
{"user": {"name": "jim"}}
{"user": {"name": "sally"}}
some random data string

```

I've tried:

```
select user_data::json#>'{user,name}' from users

```

I get: 

```
ERROR:  invalid input syntax for type json
DETAIL:  Token "some" is invalid.
CONTEXT:  JSON user_data, line 1: some...

```

Is it possible to prevent this?