[Sqlalchemy-tickets] Issue #4248: PostgreSQL: Insufficient parenthesis-wrapping for (boolean) result of `IS NULL` (zzzeek/sqlalchemy)

[Robert S. <iss...@bi...>]

New issue 4248: PostgreSQL: Insufficient parenthesis-wrapping for (boolean) result of `IS NULL`
https://bitbucket.org/zzzeek/sqlalchemy/issues/4248/postgresql-insufficient-parenthesis

Robert Scott:

Using sqlalchemy 1.1.4 with postgresql 9.6.

The result of an `IS NULL` comparison is a boolean and in postgres it is usable as such - for instance the following works:

```
db=> SELECT (123 IS NULL) = ('blah' IS NULL);
 ?column? 
----------
 t
(1 row)
```

However the following fails due to operator precedence:

```
db=> SELECT 1 IS NULL = 'blah' IS NULL;
ERROR:  invalid input syntax for type boolean: "blah"
LINE 1: SELECT 1 IS NULL = 'blah' IS NULL;
```

sqlalchemy 1.1.4 unfortunately doesn't include these parentheses:

```
>>> str(db.session.query((User.id == None) == (User.name == None)))
'SELECT users.id IS NULL = users.name IS NULL AS anon_1 \nFROM users'
```

which of course fails in a similar way. Luckily this wrapping *is* performed correctly for the result of equalities:

```
>>> str(db.session.query((User.id == 123) == (User.name == "blah")))
'SELECT (users.id = %(id_1)s) = (users.name = %(name_1)s) AS anon_1 \nFROM users'
```

and also the workaround of manually casting the result to a boolean works fine:

```
>>> str(db.session.query(db.cast(User.id == None, db.Boolean) == db.cast(User.name == None, db.Boolean)))
'SELECT CAST(users.id IS NULL AS BOOLEAN) = CAST(users.name IS NULL AS BOOLEAN) AS anon_1 \nFROM users'
```