CHAR() on inner table of LEFT JOIN wrongly converts outer join to inner join

CREATE TABLE t0 (vkey INT);

CREATE TABLE t7 (vkey INT);

INSERT INTO t0 VALUES (6);

-- t7 empty → LEFT JOIN always NULL-extends

-- Wrong (empty): CHAR() on inner column treated as null-rejecting

SELECT COUNT(*) AS c_char

FROM t0 LEFT JOIN t7 ON t0.vkey = t7.vkey

WHERE CHAR(t7.vkey) NOT LIKE 'YVR';

-- Actual: 0

-- Expected: 1

-- Correct: same value via CASE → not_null_tables not propagated

SELECT COUNT(*) AS c_case

FROM t0 LEFT JOIN t7 ON t0.vkey = t7.vkey

WHERE CHAR(CASE WHEN FALSE THEN t7.vkey ELSE t7.vkey END) NOT LIKE 'YVR';

-- Actual: 1

-- Expected: 1

-- Semantics: CHAR(NULL) is not SQL NULL

SELECT CHAR(NULL) IS NOT NULL;  -- 1

DROP TABLE t0, t7;

CREATE TABLE t1 (a INT, b INT);

INSERT INTO t1 VALUES (1,1),(2,3);

SELECT COUNT(*) FROM t1 LEFT JOIN t1 t2 ON t1.a = t2.b

WHERE CHAR(t2.b) IS NOT NULL;

-- Actual: 1

-- Expected: 2

-- SELECT-list shows the NULL-extended row still satisfies the predicate:

SELECT t1.a, t2.b, CHAR(t2.b) IS NOT NULL AS p

FROM t1 LEFT JOIN t1 t2 ON t1.a = t2.b;

-- row (2, NULL, 1) is present here but missing from the WHERE query above

DROP TABLE t1;