Do not be driven nuts by multiple nots

Multiple nots. Complex
    firstname != 'Juan' || lastname != 'Cruz'
English-speak: 
    If your firstname is not Juan or your lastname is not Cruz, therefore you are not Juan Cruz

Don't use the above, it has multiple nots. Use this:

Single not, simple. Translates well to English:
    !(firstname == 'Juan' && lastname == 'Cruz')
English-speak (reading from inside out): 
    If you are Juan Cruz, then don't.
English-speak (reading from left to right): 
    If you are not Juan Cruz, then do.
Postgres tuple test:
    (firstname, lastname) != ('Juan', 'Cruz')
Languages without tuple:
    firstname + ' ' + lastname != 'Juan Cruz'

**Schema (PostgreSQL v13)**

    create table person(firstname text, lastname text);
    
    insert into person(firstname, lastname) values
    ('Juan', 'Cruz'),
    ('Juan', 'Buen'),
    ('Michael', 'Cruz'),
    ('Michael', 'Buen');
    

---

**Query #1**

    select
        firstname, lastname,
        
        firstname != 'Juan' or lastname != 'Cruz' as test1,
        not (firstname = 'Juan' and lastname = 'Cruz') as test2,
        
        (firstname, lastname) != ('Juan', 'Cruz') as test3,
        (firstname || ' ' || lastname) != 'Juan Cruz' as test4
        
    from 
    	person;

| firstname | lastname | test1 | test2 | test3 | test4 |
| --------- | -------- | ----- | ----- | ----- | ----- |
| Juan      | Cruz     | false | false | false | false |
| Juan      | Buen     | true  | true  | true  | true  |
| Michael   | Cruz     | true  | true  | true  | true  |
| Michael   | Buen     | true  | true  | true  | true  |

---

[View on DB Fiddle](https://www.db-fiddle.com/f/nxbuszjT4zgmdj4pGaZeuQ/0)


-------------

Multiple nots. Complex
    firstname != 'Juan' && lastname != 'Cruz'

Single not, simple. Translates well to English:
    !(firstname == 'Juan' || lastname == 'Cruz')
English-speak: 
    If your firstname is Juan or lastname is Cruz, then don't.


**Schema (PostgreSQL v13)**

    create table person(firstname text, lastname text);
    
    insert into person(firstname, lastname) values
    ('Juan', 'Cruz'),
    ('Juan', 'Buen'),
    ('Michael', 'Cruz'),
    ('Michael', 'Buen');
    

---

**Query #1**

    select
        firstname, lastname,
        
        firstname != 'Juan' and lastname != 'Cruz' as test1,
        not (firstname = 'Juan' or lastname = 'Cruz') as test2
        
    from 
    	person;

| firstname | lastname | test1 | test2 |
| --------- | -------- | ----- | ----- |
| Juan      | Cruz     | false | false |
| Juan      | Buen     | false | false |
| Michael   | Cruz     | false | false |
| Michael   | Buen     | true  | true  |

---

[View on DB Fiddle](https://www.db-fiddle.com/f/nxbuszjT4zgmdj4pGaZeuQ/1)