Urgent - SQL left join bug?

On Wed, Jun 21, 2017 at 9:06 AM, Kaijiang Chen <chenkaijiang@gmail.com>
wrote:

Hi, I'm running PostgreSQL 9.4.10 on CentOS 6.5. It looks like that I
found a bug with left join. It is very URGENT since it is running in the
production servers.

### Conditions: ###

I have 2 tables:

TABLE 1: (2171209 records)
\d prescription_herbs
Table
"public.prescription_herbs"
Column | Type |
Modifiers
---------------------+--------------------------------+-----
------------------------------------------------------------
id | integer | not null default
nextval('prescription_herbs_id_seq'::regclass)
prescription_id | integer | not null
herb_id | integer | not null
weight | integer | not null
created_at | timestamp(0) without time zone | not null
updated_at | timestamp(0) without time zone | not null
deleted_at | timestamp(0) without time zone |
price | numeric(10,5) |
special_manufacture | character varying(255) |
cost | numeric(10,5) |
pharmacy_id | integer |
Indexes:
"prescription_herbs_pkey" PRIMARY KEY, btree (id)
"prescription_herbs_hid" btree (herb_id)
"prescription_herbs_prid" btree (prescription_id)

TABLE 2: (4406 records)

\d pharmacy_herbs
Table "public.pharmacy_herbs"
Column | Type |
Modifiers
-------------+--------------------------------+-------------
------------------------------------------------
id | integer | not null default
nextval('pharmacy_herbs_id_seq'::regclass)
pharmacy_id | integer |
herb_id | integer |
cost | numeric(10,5) |
price | numeric(10,5) |
no | character varying(255) |
deleted_at | timestamp(0) without time zone |
created_at | timestamp(0) without time zone | not null
updated_at | timestamp(0) without time zone | not null
name | character varying(255) |
Indexes:
"pharmacy_herbs_pkey" PRIMARY KEY, btree (id)
"pharmacy_herbs_herb_id" btree (herb_id)

### BUG: ###

I ran a SQL:
select pha.id,ph.herb_id,pha.name,ph.weight
from prescription_herbs as ph *left join* pharmacy_herbs as pha on
ph.herb_id=pha.herb_id
where ph.prescription_id=116285 and ph.deleted_at is null and
pha.deleted_at is null and pha.pharmacy_id=22 order by ph.herb_id;

Expected:

It should have 10 rows because the SQL "select * from prescription_herbs
as ph where ph.prescription_id=116285 and ph.deleted_at is null" returned
10 rows and I'm using *LEFT JOIN *in the above SQL.

Actual Result:

It returned only 9 rows and the result is the same as JOIN (not LEFT
JOIN).

### More info: ###

I explain the SQL:
explain select pha.id,ph.herb_id,pha.name,ph.weight
from prescription_herbs as ph left join pharmacy_herbs as pha on
ph.herb_id=pha.herb_id
where ph.prescription_id=116285 and ph.deleted_at is null and
pha.deleted_at is null and pha.pharmacy_id=22 order by ph.herb_id;

I got:

Sort (cost=131.73..131.76 rows=10 width=24)
Sort Key: ph.herb_id
-> * Hash Join* (cost=122.02..131.56 rows=10 width=24)
Hash Cond: (ph.herb_id = pha.herb_id)
-> Index Scan using prescription_herbs_prid on
prescription_herbs ph (cost=0.43..9.68 rows=23 width=8)
Index Cond: (prescription_id = 116285)
Filter: (deleted_at IS NULL)
-> Hash (cost=113.08..113.08 rows=681 width=20)
-> Seq Scan on pharmacy_herbs pha (cost=0.00..113.08
rows=681 width=20)
Filter: ((deleted_at IS NULL) AND (pharmacy_id = 22))

I think the above* "Hash Join" SHOULD BE "Hash Left Join"*, right?

I tried to explain another SQL:
explain select * from doctors d left join prescriptions p on d.id
=p.doctor_id;

I got:
Hash Right Join (cost=2159.33..31453.58 rows=130330 width=2936)
Hash Cond: (p.doctor_id = d.id)
-> Seq Scan on prescriptions p (cost=0.00..9273.30 rows=130330
width=495)
-> Hash (cost=576.37..576.37 rows=5037 width=2441)
-> Seq Scan on doctors d (cost=0.00..576.37 rows=5037
width=2441)

The "Hash Right Join" is the correct node.

Any help is very appreciated! WAITING...

Thanks,
Kaijiang

This is not a bug. The conditions of the "right" table pha - basically
(pha.pharmacy_id=22) and secondary ((pha.deleted_at is null) )- that you
have put in the WHERE clause make the query act as if it was an INNER join.

Move them to the ON and you'll get your 10 rows.

select ...
from prescription_herbs as ph *left join* pharmacy_herbs as pha
on ph.herb_id=pha.herb_id and pha.deleted_at is null and
pha.pharmacy_id=22
where ph.prescription_id=116285 and ph.deleted_at is null
order by ...

The (pha.deleted_at is null) part may give different results depending on
where it is placed (ON vs WHERE) but my guess - since you want all the 10
rows of the left table - is that it should be in ON, too

Pantelis

Hi, Pantelis and Heikki, thank you very much for such a quick response!

I got it. I was so silly.....

On Wed, Jun 21, 2017 at 4:23 PM, Pantelis Theodosiou <ypercube@gmail.com>
wrote:

On Wed, Jun 21, 2017 at 9:06 AM, Kaijiang Chen <chenkaijiang@gmail.com>
wrote:

Hi, I'm running PostgreSQL 9.4.10 on CentOS 6.5. It looks like that I
found a bug with left join. It is very URGENT since it is running in the
production servers.

### Conditions: ###

I have 2 tables:

TABLE 1: (2171209 records)
\d prescription_herbs
Table
"public.prescription_herbs"
Column | Type |
Modifiers
---------------------+--------------------------------+-----
------------------------------------------------------------
id | integer | not null default
nextval('prescription_herbs_id_seq'::regclass)
prescription_id | integer | not null
herb_id | integer | not null
weight | integer | not null
created_at | timestamp(0) without time zone | not null
updated_at | timestamp(0) without time zone | not null
deleted_at | timestamp(0) without time zone |
price | numeric(10,5) |
special_manufacture | character varying(255) |
cost | numeric(10,5) |
pharmacy_id | integer |
Indexes:
"prescription_herbs_pkey" PRIMARY KEY, btree (id)
"prescription_herbs_hid" btree (herb_id)
"prescription_herbs_prid" btree (prescription_id)

TABLE 2: (4406 records)

\d pharmacy_herbs
Table "public.pharmacy_herbs"
Column | Type |
Modifiers
-------------+--------------------------------+-------------
------------------------------------------------
id | integer | not null default
nextval('pharmacy_herbs_id_seq'::regclass)
pharmacy_id | integer |
herb_id | integer |
cost | numeric(10,5) |
price | numeric(10,5) |
no | character varying(255) |
deleted_at | timestamp(0) without time zone |
created_at | timestamp(0) without time zone | not null
updated_at | timestamp(0) without time zone | not null
name | character varying(255) |
Indexes:
"pharmacy_herbs_pkey" PRIMARY KEY, btree (id)
"pharmacy_herbs_herb_id" btree (herb_id)

### BUG: ###

I ran a SQL:
select pha.id,ph.herb_id,pha.name,ph.weight
from prescription_herbs as ph *left join* pharmacy_herbs as pha on
ph.herb_id=pha.herb_id
where ph.prescription_id=116285 and ph.deleted_at is null and
pha.deleted_at is null and pha.pharmacy_id=22 order by ph.herb_id;

Expected:

It should have 10 rows because the SQL "select * from prescription_herbs
as ph where ph.prescription_id=116285 and ph.deleted_at is null" returned
10 rows and I'm using *LEFT JOIN *in the above SQL.

Actual Result:

It returned only 9 rows and the result is the same as JOIN (not LEFT
JOIN).

### More info: ###

I explain the SQL:
explain select pha.id,ph.herb_id,pha.name,ph.weight
from prescription_herbs as ph left join pharmacy_herbs as pha on
ph.herb_id=pha.herb_id
where ph.prescription_id=116285 and ph.deleted_at is null and
pha.deleted_at is null and pha.pharmacy_id=22 order by ph.herb_id;

I got:

Sort (cost=131.73..131.76 rows=10 width=24)
Sort Key: ph.herb_id
-> * Hash Join* (cost=122.02..131.56 rows=10 width=24)
Hash Cond: (ph.herb_id = pha.herb_id)
-> Index Scan using prescription_herbs_prid on
prescription_herbs ph (cost=0.43..9.68 rows=23 width=8)
Index Cond: (prescription_id = 116285)
Filter: (deleted_at IS NULL)
-> Hash (cost=113.08..113.08 rows=681 width=20)
-> Seq Scan on pharmacy_herbs pha (cost=0.00..113.08
rows=681 width=20)
Filter: ((deleted_at IS NULL) AND (pharmacy_id =
22))

I think the above* "Hash Join" SHOULD BE "Hash Left Join"*, right?

I tried to explain another SQL:
explain select * from doctors d left join prescriptions p on d.id
=p.doctor_id;

I got:
Hash Right Join (cost=2159.33..31453.58 rows=130330 width=2936)
Hash Cond: (p.doctor_id = d.id)
-> Seq Scan on prescriptions p (cost=0.00..9273.30 rows=130330
width=495)
-> Hash (cost=576.37..576.37 rows=5037 width=2441)
-> Seq Scan on doctors d (cost=0.00..576.37 rows=5037
width=2441)

The "Hash Right Join" is the correct node.

Any help is very appreciated! WAITING...

Thanks,
Kaijiang

This is not a bug. The conditions of the "right" table pha - basically
(pha.pharmacy_id=22) and secondary ((pha.deleted_at is null) )- that you
have put in the WHERE clause make the query act as if it was an INNER join.

Move them to the ON and you'll get your 10 rows.

select ...
from prescription_herbs as ph *left join* pharmacy_herbs as pha
on ph.herb_id=pha.herb_id and pha.deleted_at is null and
pha.pharmacy_id=22
where ph.prescription_id=116285 and ph.deleted_at is null
order by ...

The (pha.deleted_at is null) part may give different results depending on
where it is placed (ON vs WHERE) but my guess - since you want all the 10
rows of the left table - is that it should be in ON, too

Pantelis

The correct SQL should be:

select pha.id,ph.herb_id,pha.name,ph.weight
from prescription_herbs as ph left join pharmacy_herbs as pha on
ph.herb_id=pha.herb_id *and pha.pharmacy_id=22*
where ph.prescription_id=116285 and ph.deleted_at is null and
pha.deleted_at is null order by ph.herb_id;

On Wed, Jun 21, 2017 at 4:26 PM, Kaijiang Chen <chenkaijiang@gmail.com>
wrote:

Hi, Pantelis and Heikki, thank you very much for such a quick response!

I got it. I was so silly.....

On Wed, Jun 21, 2017 at 4:23 PM, Pantelis Theodosiou <ypercube@gmail.com>
wrote:

On Wed, Jun 21, 2017 at 9:06 AM, Kaijiang Chen <chenkaijiang@gmail.com>
wrote:

Hi, I'm running PostgreSQL 9.4.10 on CentOS 6.5. It looks like that I
found a bug with left join. It is very URGENT since it is running in the
production servers.

### Conditions: ###

I have 2 tables:

TABLE 1: (2171209 records)
\d prescription_herbs
Table
"public.prescription_herbs"
Column | Type |
Modifiers
---------------------+--------------------------------+-----
------------------------------------------------------------
id | integer | not null
default nextval('prescription_herbs_id_seq'::regclass)
prescription_id | integer | not null
herb_id | integer | not null
weight | integer | not null
created_at | timestamp(0) without time zone | not null
updated_at | timestamp(0) without time zone | not null
deleted_at | timestamp(0) without time zone |
price | numeric(10,5) |
special_manufacture | character varying(255) |
cost | numeric(10,5) |
pharmacy_id | integer |
Indexes:
"prescription_herbs_pkey" PRIMARY KEY, btree (id)
"prescription_herbs_hid" btree (herb_id)
"prescription_herbs_prid" btree (prescription_id)

TABLE 2: (4406 records)

\d pharmacy_herbs
Table "public.pharmacy_herbs"
Column | Type |
Modifiers
-------------+--------------------------------+-------------
------------------------------------------------
id | integer | not null default
nextval('pharmacy_herbs_id_seq'::regclass)
pharmacy_id | integer |
herb_id | integer |
cost | numeric(10,5) |
price | numeric(10,5) |
no | character varying(255) |
deleted_at | timestamp(0) without time zone |
created_at | timestamp(0) without time zone | not null
updated_at | timestamp(0) without time zone | not null
name | character varying(255) |
Indexes:
"pharmacy_herbs_pkey" PRIMARY KEY, btree (id)
"pharmacy_herbs_herb_id" btree (herb_id)

### BUG: ###

I ran a SQL:
select pha.id,ph.herb_id,pha.name,ph.weight
from prescription_herbs as ph *left join* pharmacy_herbs as pha on
ph.herb_id=pha.herb_id
where ph.prescription_id=116285 and ph.deleted_at is null and
pha.deleted_at is null and pha.pharmacy_id=22 order by ph.herb_id;

Expected:

It should have 10 rows because the SQL "select * from
prescription_herbs as ph where ph.prescription_id=116285 and ph.deleted_at
is null" returned 10 rows and I'm using *LEFT JOIN *in the above SQL.

Actual Result:

It returned only 9 rows and the result is the same as JOIN (not LEFT
JOIN).

### More info: ###

I explain the SQL:
explain select pha.id,ph.herb_id,pha.name,ph.weight
from prescription_herbs as ph left join pharmacy_herbs as pha on
ph.herb_id=pha.herb_id
where ph.prescription_id=116285 and ph.deleted_at is null and
pha.deleted_at is null and pha.pharmacy_id=22 order by ph.herb_id;

I got:

Sort (cost=131.73..131.76 rows=10 width=24)
Sort Key: ph.herb_id
-> * Hash Join* (cost=122.02..131.56 rows=10 width=24)
Hash Cond: (ph.herb_id = pha.herb_id)
-> Index Scan using prescription_herbs_prid on
prescription_herbs ph (cost=0.43..9.68 rows=23 width=8)
Index Cond: (prescription_id = 116285)
Filter: (deleted_at IS NULL)
-> Hash (cost=113.08..113.08 rows=681 width=20)
-> Seq Scan on pharmacy_herbs pha (cost=0.00..113.08
rows=681 width=20)
Filter: ((deleted_at IS NULL) AND (pharmacy_id =
22))

I think the above* "Hash Join" SHOULD BE "Hash Left Join"*, right?

I tried to explain another SQL:
explain select * from doctors d left join prescriptions p on d.id
=p.doctor_id;

I got:
Hash Right Join (cost=2159.33..31453.58 rows=130330 width=2936)
Hash Cond: (p.doctor_id = d.id)
-> Seq Scan on prescriptions p (cost=0.00..9273.30 rows=130330
width=495)
-> Hash (cost=576.37..576.37 rows=5037 width=2441)
-> Seq Scan on doctors d (cost=0.00..576.37 rows=5037
width=2441)

The "Hash Right Join" is the correct node.

Any help is very appreciated! WAITING...

Thanks,
Kaijiang

This is not a bug. The conditions of the "right" table pha - basically
(pha.pharmacy_id=22) and secondary ((pha.deleted_at is null) )- that you
have put in the WHERE clause make the query act as if it was an INNER join.

Move them to the ON and you'll get your 10 rows.

select ...
from prescription_herbs as ph *left join* pharmacy_herbs as pha
on ph.herb_id=pha.herb_id and pha.deleted_at is null and
pha.pharmacy_id=22
where ph.prescription_id=116285 and ph.deleted_at is null
order by ...

The (pha.deleted_at is null) part may give different results depending
on where it is placed (ON vs WHERE) but my guess - since you want all the
10 rows of the left table - is that it should be in ON, too

Pantelis

Thank you PG guys! I fix the SQL and everything works so well!

On Wed, Jun 21, 2017 at 4:28 PM, Kaijiang Chen <chenkaijiang@gmail.com>
wrote:

The correct SQL should be:

select pha.id,ph.herb_id,pha.name,ph.weight
from prescription_herbs as ph left join pharmacy_herbs as pha on
ph.herb_id=pha.herb_id *and pha.pharmacy_id=22*
where ph.prescription_id=116285 and ph.deleted_at is null and
pha.deleted_at is null order by ph.herb_id;

On Wed, Jun 21, 2017 at 4:26 PM, Kaijiang Chen <chenkaijiang@gmail.com>
wrote:

Hi, Pantelis and Heikki, thank you very much for such a quick response!

I got it. I was so silly.....

On Wed, Jun 21, 2017 at 4:23 PM, Pantelis Theodosiou <ypercube@gmail.com

wrote:

On Wed, Jun 21, 2017 at 9:06 AM, Kaijiang Chen <chenkaijiang@gmail.com>
wrote:

Hi, I'm running PostgreSQL 9.4.10 on CentOS 6.5. It looks like that I
found a bug with left join. It is very URGENT since it is running in the
production servers.

### Conditions: ###

I have 2 tables:

TABLE 1: (2171209 records)
\d prescription_herbs
Table
"public.prescription_herbs"
Column | Type |
Modifiers
---------------------+--------------------------------+-----
------------------------------------------------------------
id | integer | not null
default nextval('prescription_herbs_id_seq'::regclass)
prescription_id | integer | not null
herb_id | integer | not null
weight | integer | not null
created_at | timestamp(0) without time zone | not null
updated_at | timestamp(0) without time zone | not null
deleted_at | timestamp(0) without time zone |
price | numeric(10,5) |
special_manufacture | character varying(255) |
cost | numeric(10,5) |
pharmacy_id | integer |
Indexes:
"prescription_herbs_pkey" PRIMARY KEY, btree (id)
"prescription_herbs_hid" btree (herb_id)
"prescription_herbs_prid" btree (prescription_id)

TABLE 2: (4406 records)

\d pharmacy_herbs
Table "public.pharmacy_herbs"
Column | Type |
Modifiers
-------------+--------------------------------+-------------
------------------------------------------------
id | integer | not null default
nextval('pharmacy_herbs_id_seq'::regclass)
pharmacy_id | integer |
herb_id | integer |
cost | numeric(10,5) |
price | numeric(10,5) |
no | character varying(255) |
deleted_at | timestamp(0) without time zone |
created_at | timestamp(0) without time zone | not null
updated_at | timestamp(0) without time zone | not null
name | character varying(255) |
Indexes:
"pharmacy_herbs_pkey" PRIMARY KEY, btree (id)
"pharmacy_herbs_herb_id" btree (herb_id)

### BUG: ###

I ran a SQL:
select pha.id,ph.herb_id,pha.name,ph.weight
from prescription_herbs as ph *left join* pharmacy_herbs as pha on
ph.herb_id=pha.herb_id
where ph.prescription_id=116285 and ph.deleted_at is null and
pha.deleted_at is null and pha.pharmacy_id=22 order by ph.herb_id;

Expected:

It should have 10 rows because the SQL "select * from
prescription_herbs as ph where ph.prescription_id=116285 and ph.deleted_at
is null" returned 10 rows and I'm using *LEFT JOIN *in the above SQL.

Actual Result:

It returned only 9 rows and the result is the same as JOIN (not LEFT
JOIN).

### More info: ###

I explain the SQL:
explain select pha.id,ph.herb_id,pha.name,ph.weight
from prescription_herbs as ph left join pharmacy_herbs as pha on
ph.herb_id=pha.herb_id
where ph.prescription_id=116285 and ph.deleted_at is null and
pha.deleted_at is null and pha.pharmacy_id=22 order by ph.herb_id;

I got:

Sort (cost=131.73..131.76 rows=10 width=24)
Sort Key: ph.herb_id
-> * Hash Join* (cost=122.02..131.56 rows=10 width=24)
Hash Cond: (ph.herb_id = pha.herb_id)
-> Index Scan using prescription_herbs_prid on
prescription_herbs ph (cost=0.43..9.68 rows=23 width=8)
Index Cond: (prescription_id = 116285)
Filter: (deleted_at IS NULL)
-> Hash (cost=113.08..113.08 rows=681 width=20)
-> Seq Scan on pharmacy_herbs pha (cost=0.00..113.08
rows=681 width=20)
Filter: ((deleted_at IS NULL) AND (pharmacy_id =
22))

I think the above* "Hash Join" SHOULD BE "Hash Left Join"*, right?

I tried to explain another SQL:
explain select * from doctors d left join prescriptions p on d.id
=p.doctor_id;

I got:
Hash Right Join (cost=2159.33..31453.58 rows=130330 width=2936)
Hash Cond: (p.doctor_id = d.id)
-> Seq Scan on prescriptions p (cost=0.00..9273.30 rows=130330
width=495)
-> Hash (cost=576.37..576.37 rows=5037 width=2441)
-> Seq Scan on doctors d (cost=0.00..576.37 rows=5037
width=2441)

The "Hash Right Join" is the correct node.

Any help is very appreciated! WAITING...

Thanks,
Kaijiang

This is not a bug. The conditions of the "right" table pha - basically
(pha.pharmacy_id=22) and secondary ((pha.deleted_at is null) )- that you
have put in the WHERE clause make the query act as if it was an INNER join.

Move them to the ON and you'll get your 10 rows.

select ...
from prescription_herbs as ph *left join* pharmacy_herbs as pha
on ph.herb_id=pha.herb_id and pha.deleted_at is null and
pha.pharmacy_id=22
where ph.prescription_id=116285 and ph.deleted_at is null
order by ...

The (pha.deleted_at is null) part may give different results depending
on where it is placed (ON vs WHERE) but my guess - since you want all the
10 rows of the left table - is that it should be in ON, too

Pantelis