Inconsistent capitalisation of boolean or null literal SQL-L040

Inconsistent capitalisation of literals is considered unidiomatic in sql.

Bad practice

In this example, null and false are in lower-case whereas TRUE is in upper-case.

select
    a,
    null,
    TRUE,
    false
from foo

Recommended

select
    a,
    NULL,
    TRUE,
    FALSE
from foo

-- Also good

select
    a,
    null,
    true,
    false
from foo