psql (9.6.1, server 9.5.5)
employees
Column | Type | Modifiers | Storage | Stats target | Description
----------------+-----------------------------+-----------------------------------------------------------------+----------+--------------+---- ---------
employee_id | integer | not null default nextval('employees_employee_id_seq'::regclass) | plain | |
first_name | character varying(20) | | extended | |
last_name | character varying(25) | not null | extended | |
email | character varying(25) | not null | extended | |
phone_number | character varying(20) | | extended | |
hire_date | timestamp without time zone | not null | plain | |
job_id | character varying(10) | not null | extended | |
salary | numeric(8,2) | | main | |
commission_pct | numeric(2,2) | | main | |
manager_id | integer | | plain | |
department_id | integer
For self education I'd like to use a variable.
The result of this request would suit me:
hr=> select last_name, char_length(last_name) as Length from employees where substring(last_name from 1 for 1) = 'H' order by last_name;
last_name | length
-----------+--------
Hartstein | 9
Higgins | 7
Hunold | 6
(3 rows)
But for self education I'd like to use a variable:
\set chosen_letter 'H'
hr=> select last_name, char_length(last_name) as Length from employees where substring(last_name from 1 for 1) = :chosen_letter order by last_name;
ERROR: column "h" does not exist
LINE 1: ...ployees where substring(last_name from 1 for 1) = H order by...
^
Those apostrophes seems to ruin everything. And I can't cope with the problem.
Could you help me understand how to use variable to acquire the result as above?
Try using:
\set chosen_letter '''H'''
Related
I dumped a database and imported it into a different server. One of the tables has a bytea column and has a single row of data. On the original server, if I SELECT * FROM users;, it shows the correct value as #. - however, when I do that same select statement on the second server, I get \x402e for that same field. I have tried to wrap my head around this column type but it is over my head. Why would it appear as an escaped string on one server but not the other? Both servers are running Pg11 and I am accessing both via psql.
Original Server:
=# \d+ users
Table "public.users"
Column | Type | Collation | Nullable | Default | Storage | Stats target | Description
-----------+------------------------+-----------+----------+-----------------------------------+----------+--------------+-------------
id | integer | | not null | nextval('users_id_seq'::regclass) | plain | |
priority | integer | | not null | 7 | plain | |
policy_id | integer | | not null | 1 | plain | |
email | bytea | | not null | | extended | |
fullname | character varying(255) | | | NULL::character varying | extended | |
=# SELECT * FROM users;
id | priority | policy_id | email | fullname
----+----------+-----------+-------+----------
1 | 0 | 1 | #. |
(1 row)
Secondary Server:
=> \d+ users
Table "public.users"
Column | Type | Collation | Nullable | Default | Storage | Stats target | Description
-----------+------------------------+-----------+----------+-----------------------------------+----------+--------------+-------------
id | integer | | not null | nextval('users_id_seq'::regclass) | plain | |
priority | integer | | not null | 7 | plain | |
policy_id | integer | | not null | 1 | plain | |
email | bytea | | not null | | extended | |
fullname | character varying(255) | | | NULL::character varying | extended | |
=> SELECT * FROM users;
id | priority | policy_id | email | fullname
----+----------+-----------+--------+----------
4 | 0 | 1 | \x402e |
(1 row)
set bytea_output to hex;
select '#.'::bytea;
┌────────┐
│ bytea │
├────────┤
│ \x402e │
└────────┘
set bytea_output to escape;
select '#.'::bytea;
┌───────┐
│ bytea │
├───────┤
│ #. │
└───────┘
It seems that you have a different settings at your servers.
Documentation
I have a function below (is_organizer) that works, and lets me use this method as a computed field in Hasura. The function below (is_chapter_member) which is almost identical, doesn't work.
WORKS
CREATE OR REPLACE FUNCTION is_organizer(event_row events, hasura_session json)
RETURNS boolean AS $$
SELECT EXISTS (
SELECT 1
FROM event_organizers o
WHERE
o.user_id::text = hasura_session->>'x-hasura-user-id'
AND
(event_row.id = o.event_id OR event_row.event_template_id = o.event_template_id)
);
$$ LANGUAGE SQL STRICT IMMUTABLE;
BROKEN
CREATE OR REPLACE FUNCTION is_chapter_member(c chapters, hasura_session json)
RETURNS boolean AS $$
SELECT EXISTS (
SELECT 1
FROM chapter_members m
WHERE
m.user_id::text = hasura_session->>'x-hasura-user-id'
AND
c.chapter_id = m.chapter_id
);
$$ LANGUAGE SQL STRICT IMMUTABLE;
When attempting to add this function (not call it, just create it) Postgres gives me the following error:
ERROR: missing FROM-clause entry for table "c"
LINE 9: c.chapter_id = m.chapter_id
Why would a function param need a where clause? Table dumps below...
Table "public.chapters"
Column | Type | Collation | Nullable | Default
-----------------+--------------------------+-----------+----------+--------------------------------------
id | integer | | not null | nextval('chapters_id_seq'::regclass)
title | text | | not null |
slug | text | | not null |
description | jsonb | | |
avatar_url | text | | |
photo_url | text | | |
region | text | | |
maps_api_result | jsonb | | |
lat | numeric(11,8) | | |
lng | numeric(11,8) | | |
created_at | timestamp with time zone | | not null | now()
updated_at | timestamp with time zone | | not null | now()
deleted_at | timestamp with time zone | | |
Table "public.chapter_members"
Column | Type | Collation | Nullable | Default
------------+--------------------------+-----------+----------+---------
user_id | integer | | not null |
chapter_id | integer | | not null |
created_at | timestamp with time zone | | not null | now()
updated_at | timestamp with time zone | | not null | now()
Table "public.events"
Column | Type | Collation | Nullable | Default
-------------------+-----------------------------+-----------+----------+---------------------------------------------------
id | integer | | not null | nextval('events_id_seq'::regclass)
event_template_id | integer | | not null |
venue_id | integer | | |
starts_at | timestamp without time zone | | not null |
duration | interval | | not null |
title | text | | |
slug | text | | |
description | text | | |
photo_url | text | | |
created_at | timestamp without time zone | | not null | now()
updated_at | timestamp without time zone | | not null | now()
deleted_at | timestamp without time zone | | |
ends_at | timestamp without time zone | | | generated always as (starts_at + duration) stored
Table "public.event_organizers"
Column | Type | Collation | Nullable | Default
-------------------+---------+-----------+----------+----------------------------------------------
id | integer | | not null | nextval('event_organizers_id_seq'::regclass)
user_id | integer | | not null |
event_id | integer | | |
event_template_id | integer | | |
This turned out to be using an incorrect column name in the broken function. chapter_id should have just been id on the c argument. I took Richard's prompt and tried putting parens around the arg like (c).chapter_id. This then correctly told me that chapter_id doesn't exist, and allowed me to fix the issue.
I have implemented a tagging system in my application, using Postgres 9.6. There are three tables.
Projects
Table "public.project"
Column | Type | Collation | Nullable | Default
-------------+-----------------------------+-----------+----------+---------------------------------
id | integer | | not null | nextval('tag_id_seq'::regclass)
name | character varying(255) | | not null |
user_id | integer | | |
Tags
Table "public.tag"
Column | Type | Collation | Nullable | Default
-------------+-----------------------------+-----------+----------+---------------------------------
id | integer | | not null | nextval('tag_id_seq'::regclass)
tag | character varying(255) | | not null |
user_id | integer | | |
is_internal | boolean | | not null | false
Project tags
Column | Type | Collation | Nullable | Default
------------------+-----------------------------+-----------+----------+-----------------------------------------
id | integer | | not null | nextval('project_tag_id_seq'::regclass)
tag_id | integer | | not null |
project_id | integer | | | |
user_id | integer | | not null |
Now I want to get a list of all the projects, annotated with a column that indicates (for a particular tag) whether it has that tag.
So I'd like the results to look like this:
id name has_favorite_tag
1 foo true
2 bar false
3 baz false
This is my query so far:
select project.*, CASE(XXXX) as has_project_tag
from project p
join (select * from project_tag where tag_id=1) pt on p.id=pt.project_id
I know that I want to use CASE to be true when the length of project_tag matches is greater than 0 - but how do I do this?
(In reality the project table has many more fields, of course.)
Here's a possibility (unfiltered for tag_id; add to inner select if necessary):
select project.*, exists(select * from project_tag where id=project.id) as has_project_tag from project;
In PostgreSQL 9 on CentOS 6 there are 60000 records in pref_users table:
# \d pref_users
Table "public.pref_users"
Column | Type | Modifiers
------------+-----------------------------+--------------------
id | character varying(32) | not null
first_name | character varying(64) | not null
last_name | character varying(64) |
login | timestamp without time zone | default now()
last_ip | inet |
(... more columns skipped...)
And another table holds around 500 ids of users which are not allowed to play anymore:
# \d pref_ban2
Table "public.pref_ban2"
Column | Type | Modifiers
------------+-----------------------------+---------------
id | character varying(32) | not null
first_name | character varying(64) |
last_name | character varying(64) |
city | character varying(64) |
last_ip | inet |
reason | character varying(128) |
created | timestamp without time zone | default now()
Indexes:
"pref_ban2_pkey" PRIMARY KEY, btree (id)
In a PHP script I am trying to display all 60000 users from pref_users in a jQuery-dataTable. And I would like to mark the banned users (the users found in pref_ban2).
Which means I need a column named ban for each record in my query holding true or false.
So I am trying a left outer join query:
# select
b.id, -- how to make this column a boolean?
u.id,
u.first_name,
u.last_name,
u.city,
u.last_ip,
to_char(u.login, 'DD.MM.YYYY') as day
from pref_users u left outer join pref_ban2 b on u.id=b.id
limit 10;
id | id | first_name | last_name | city | last_ip | day
----+----------+-------------+-----------+-------------+-----------------+------------
| DE1 | Alex | | Bochum | 2.206.0.224 | 21.11.2014
| DE100032 | Княжна Мэри | | London | 151.50.61.131 | 01.02.2014
| DE10011 | Aлександр Ш | | Симферополь | 37.57.108.13 | 01.01.2014
| DE10016 | Semen10 | | usa | 69.123.171.15 | 25.06.2014
| DE10018 | Горловка | | Горловка | 178.216.97.214 | 25.09.2011
| DE10019 | -Дмитрий- | | пермь | 5.140.81.95 | 21.11.2014
| DE10047 | Василий | | Cумы | 95.132.42.185 | 25.07.2014
| DE10054 | Maedhros | | Чикаго | 207.246.176.110 | 26.06.2014
| DE10062 | ssergw | | москва | 46.188.125.206 | 12.09.2014
| DE10086 | Вадим | | Тула | 109.111.26.176 | 26.02.2012
(10 rows)
As you can see the b.id column above is empty - because these 10 users aren't banned.
How to get a false value in that column instead of a String?
And I am not after some coalesceor case expression, but am looking for "the proper" way to do such a query.
"IS NULL" and "IS NOT NULL" return a boolean, so this should make it easy.
I think this is all you need?
SELECT
b.id IS NOT NULL as is_banned, -- The value of "is_banned" will be a boolean
Not sure if you need the "NOT" or not, but you'll get a bool either way.
A CASE or COALESCE statement with an outer join IS the proper way to do this.
select
CASE
WHEN b.id IS NULL THEN true
ELSE false
END AS banned,
u.id,
u.first_name,
u.last_name,
u.city,
u.last_ip,
to_char(u.login, 'DD.MM.YYYY') as day
from pref_users u
left outer join pref_ban2 b
on u.id=b.id
limit 10;
I want to get the last comment in a conversation between two people.
My table structure as follows:
Table "public.comments"
Column | Type | Modifiers | Storage | Stats target | Description
-------------+-----------------------------+-------------------------------------------------------+----------+--------------+-------------
id | integer | not null default nextval('comments_id_seq'::regclass) | plain | |
body | text | not null | extended | |
target_id | integer | | plain | |
target_type | character varying(255) | | extended | |
created_at | timestamp without time zone | not null | plain | |
updated_at | timestamp without time zone | not null | plain | |
user_id | integer | | plain | |
My Attempt:
SELECT
comments.id,
max(SELECT id comments.created_at),
CASE
WHEN user_id = 1 THEN CONCAT(user_id,'_',target_id)
WHEN target_id = 1 THEN CONCAT(target_id,'_',user_id)
END
FROM comments
WHERE
comments.user_id = 1
OR
(comments.target_type = 'User'
AND
comments.target_id = 1)
GROUP BY
CASE
WHEN user_id = 1 THEN CONCAT(user_id,'_',target_id)
WHEN target_id = 1 THEN CONCAT(target_id,'_',user_id)
END
So I figured out how to group the comments but how to order by created_at and get the latest id and information is where I'm stuck.