Major Description
Phoenix doesn't handle NULLs consistently with other SQL dialects, and it doesn't handle them consistently internally either.
In PHOENIX-2422, jamestaylor mentioned that Phoenix's intended behavior is for empty string and NULL to be equivalent. That's inconsistent with other SQL dialects (in which NULL is never equal to anything, including itself), but if that's our documented behavior, then that's fine unless PHOENIX-2422 to change it is ever worked.
But consider the following queries:
SELECT COUNT(*) FROM SYSTEM.CATALOG WHERE TENANT_ID = '';
-- Returns 0 rows
SELECT COUNT(*) FROM SYSTEM.CATALOG WHERE TENANT_ID IS NULL;
-- Returns some number of rows. Call it N
SELECT COUNT(*) FROM SYSTEM.CATALOG WHERE TENANT_ID IN ('');
-- Returns 0 rows
SELECT COUNT(*) FROM SYSTEM.CATALOG WHERE TENANT_ID IN ('', 'FOO');
-- Returns N rows. Note that FOO does not exist, and is just a nonsense string
SELECT COUNT(*) FROM SYSTEM.CATALOG WHERE TENANT_ID = '' OR TENANT_ID = 'FOO'
--Returns 0 rows, but slowly