
Consider the test case below. It is unexpected that the second query return `2 NULL`, as `t0.c0` and `t0.c0 IS NULL` could not be evaluated to `True` at the same time.

```sql
DROP TABLE t0;
DROP TABLE t1;

CREATE TABLE t0(c0 VARCHAR);
CREATE TABLE t1(c0 INTEGER);
INSERT INTO t1 (c0) VALUES (2);

SELECT * FROM t1 LEFT  JOIN t0 ON 1; -- 2 NULL
SELECT * FROM t1 LEFT  JOIN t0 ON 1 WHERE t0.c0; -- 2 NULL (unexpected)
SELECT * FROM t1 LEFT  JOIN t0 ON 1 WHERE t0.c0 IS NULL; -- 2 NULL
```

Here's the version I used

```
docker run -i -t pkleef/virtuoso-opensource-7 version

[pkleef/virtuoso-opensource-7:7.2.12-r17.2-g466615d-ubuntu]

This Docker image is using the following version of Virtuoso:

Virtuoso Open Source Edition (Column Store) (multi threaded)
Version 7.2.12-dev.3238-pthreads as of Jan 12 2024 (9df21ea5c)
Compiled for Linux (x86_64-ubuntu_bionic-linux-gnu)
Copyright (C) 1998-2024 OpenLink Software
```

Unexpected Results when using `LEFT JOIN` with `NULL`
This is a GitHub Issue
repo:virtuoso-opensource
owner:openlink
Title : Unexpected Results when using `LEFT JOIN` with `NULL`
Issue date:

--- start body ---

Consider the test case below. It is unexpected that the second query return `2 NULL`, as `t0.c0` and `t0.c0 IS NULL` could not be evaluated to `True` at the same time.

```sql
DROP TABLE t0;
DROP TABLE t1;

CREATE TABLE t0(c0 VARCHAR);
CREATE TABLE t1(c0 INTEGER);
INSERT INTO t1 (c0) VALUES (2);

SELECT * FROM t1 LEFT  JOIN t0 ON 1; -- 2 NULL
SELECT * FROM t1 LEFT  JOIN t0 ON 1 WHERE t0.c0; -- 2 NULL (unexpected)
SELECT * FROM t1 LEFT  JOIN t0 ON 1 WHERE t0.c0 IS NULL; -- 2 NULL
```

Here's the version I used

```
docker run -i -t pkleef/virtuoso-opensource-7 version

[pkleef/virtuoso-opensource-7:7.2.12-r17.2-g466615d-ubuntu]

This Docker image is using the following version of Virtuoso:

Virtuoso Open Source Edition (Column Store) (multi threaded)
Version 7.2.12-dev.3238-pthreads as of Jan 12 2024 (9df21ea5c)
Compiled for Linux (x86_64-ubuntu_bionic-linux-gnu)
Copyright (C) 1998-2024 OpenLink Software
```

--- end body ---
