为什么 MySQL 的 IS TRUE、IS NOT TRUE、IS FALSE、IS NOT FALSE 的行为在 WHERE 和 HAVING 之间是不同的

Question

Consider two tables:

table1

id
1
2
3

table2

id, deleted
2, 0
3, 1

Suppose I want to get all rows from table1 that have not been marked "deleted" in table2, ie row 1 and 2. Consider the following SQL (in MySQL):

SELECT id
FROM table1
LEFT JOIN table2 USING (id)
WHERE deleted <> 1

This SQL obviously returns just row with id = 2.

I can do a perversion like this:

SELECT id
FROM table1
LEFT JOIN table2 USING (id)
WHERE COALESCE(deleted, 0) = 0

And then I'll get row 1 and 2.

But I wanted a more elegant way. MySQL has these nice checks for booleans, IS TRUE, IS NOT TRUE, IS FALSE, IS NOT FALSE that take NULL values into account. So consider this:

SELECT id, deleted, deleted IS NOT TRUE
FROM table1
LEFT JOIN table2 USING (id)

The result:

id, deleted, deleted IS NOT TRUE
1, NULL, TRUE
2, 0, TRUE
3, 1, FALSE

Looks great, right? now if I just put this into the WHERE clause:

SELECT id
FROM table1
LEFT JOIN table2 USING (id)
WHERE deleted IS NOT TRUE

Oh no! I get just row 2 again!

However, if I put the condition into HAVING clause, it starts working:

SELECT id
FROM table1
LEFT JOIN table2 USING (id)
HAVING deleted IS NOT TRUE

I get row 1 and 2.

Totally baffling. Seems like a bug in MySQL.

Answer 1

As I suspected and as pointed out by @BillKarwin, this is an old 2012 bug in MySQL :(

"WHERE var IS NOT TRUE yields too little" ( https://bugs.mysql.com/bug.php?id=67732 )

Answer 2

I think you just want NOT EXISTS :

SELECT t1.id
FROM table1 t1 
WHERE NOT EXISTS (SELECT 1
                  FROM table2 t2
                  WHERE t1.id = t2.id AND t2.is_deleted = 1
                 );