MariaDB 10.5

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create table emp ( 
    emp_no int not null primary key, 
    title varchar(10) not null, 
    salary int not null
    , 
        constraint c1 check (emp_no > 0), 
        constraint c2 check (title in ('BOSS','WORK'))
);

--insert into emp with t (n) as (
--    values (1) 
--    union all 
--    select n+1 from t where n+1 < 1000
--) select n, case when mod(n,10) = 0 then 'BOSS' else 'WORK' end, 
--            case when mod(n,10) = 0 then 110 else 0 end + mod(n,90) 
--from t;

-- (TITLE = BOSS) => (SALARY > 100)
alter table emp add constraint cc1 
    CHECK ( (title <> 'BOSS' OR salary > 100) );
-- (TITLE = WORK) => (SALARY <= 100)
alter table emp add constraint cc2
    CHECK ( (title <> 'WORK' OR salary <= 100) );
-- SQL-Server
-- SET SHOWPLAN_XML ON;
explain 
select * 
from emp 
where title = 'BOSS' and salary <= 100;


id
select_type
table
type
possible_keys
key
key_len
ref
rows
Extra


1
SIMPLE
emp
ALL
null
null
null
null
1
Using where


explain
select * 
from emp 
where title = 'BOSS' and salary <= 100 and 1=0


id
select_type
table
type
possible_keys
key
key_len
ref
rows
Extra


1
SIMPLE
null
null
null
null
null
null
null
Impossible WHERE


explain
select * 
from emp 
where title = 'BOSS' and salary <= 100 and ( (title <> 'BOSS' OR salary > 100) )


id
select_type
table
type
possible_keys
key
key_len
ref
rows
Extra


1
SIMPLE
emp
ALL
null
null
null
null
1
Using where


explain
select * 
from emp 
where title = 'BOSS' and salary <= 100 and ( NOT (title = 'BOSS' AND salary <= 100) )


id
select_type
table
type
possible_keys
key
key_len
ref
rows
Extra


1
SIMPLE
emp
ALL
null
null
null
null
1
Using where