I'm quite new to PostgreSQL, so maybe I'm getting some noob error I cannot recognize, so please, tell me why I cannot get this data deleted.
This is what is happening:
DELETE FROM userprofile WHERE user LIKE (SELECT User FROM User WHERE username LIKE 'testuser');
ERROR: column "username" does not exist
LINE 1: ...file WHERE user LIKE (SELECT User FROM User WHERE username L...
As I'm using django user, I know that username does exists, so, how can I get it deleted?
Chances are (stab in the dark for lack of information) you didn't think of lower-case names.
Start by reading the manual about identifiers.
What do you get for:
SELECT n.nspname, c.relname, a.attnum, a.attname
FROM pg_class c
JOIN pg_attribute a ON a.attrelid = c.oid
JOIN pg_namespace n ON n.oid = c.relnamespace
WHERE c.relname ilike 'user'
AND NOT a.attisdropped -- no dropped (dead) columns
AND a.attnum > 0 -- no system cols
ORDER BY 1,2,3
Pay attention to capitalization of identifiers. Why? Follow the link to the manual above.
You also seem to be confusing the name of a column with a value stored in this column. The error message complains about the name, because it does not exist.
And you should never use reserved words like user as identifiers to avoid problems like the one at hand. Those need to be enclosed in double-quotes at all times.
Related
The goal is to get the table and column which are "using" a sequence, and the query I've come up with is this:
select attrelid::regclass::text, attname
from pg_attribute
where pg_get_serial_sequence(attrelid::regclass::text, attname) = 'public.websession_idcntr_seq';
It's inefficient so any other suggestions are also welcome, but the problem at hand is that this breaks with the following error:
ERROR: permission denied for schema pg_toast
So the next thing I did was try to avoid pg_toast:
select attrelid::regclass::text, attname
from pg_attribute
join pg_class tbl on tbl.oid = pg_attribute.attrelid
join pg_namespace nsp on tbl.relnamespace = nsp.oid
where
nsp.nspname != 'pg_toast'
and pg_get_serial_sequence(attrelid::regclass::text, attname) = 'public.websession_idcntr_seq';
That also fails with exactly the same message.
I have no intention of doing anything with the pg_toast schema, and I can't run this under a superuser account. (EDIT: And I can't modify permissions to get around that).
Why doesn't the workaround with nspname != 'pg_toast' work?
Is there a better way to do this whole operation?
SQL does not guarantee you a certain order in which the conditions in the WHERE clause are evaluated, and EXPLAIN will show you that pg_get_serial_sequence (which causes the error) is executed first.
Try the following that excludes the offending tables earlier on:
SELECT t.oid::regclass, a.attname
FROM pg_class AS t
JOIN pg_attribute AS a ON t.oid = a.attrelid
WHERE t.relkind IN ('r', 'p') /* only normal and partitioned tables */
AND pg_get_serial_sequence(t.oid::regclass::text, attname)
= 'public.websession_idcntr_seq';
For a physical table, I have been using the following SQL:
select column_name, data_type, character_maximum_length
from INFORMATION_SCHEMA.COLUMNS
where table_name = 'a_table_name'
I found that this doesn't work for a view. Is there a way to get the schema of a view by running a SQL command (not via psql).
Postgres has dedicated System Catalog Information Functions to help with that.
To get the full view definition:
SELECT pg_get_viewdef('public.view_name');
Schema-qualification is optional. If no schema is prefixed, the current search_path setting decides visibility.
A quick hack would be to just:
SELECT * FROM public.view_name LIMIT 0;
Depending on your client, column names and types should still be displayed. Or LIMIT n to get some sample values, too. The underlying query is actually executed then (unlike with LIMIT 0).
To list columns and their data type, in order, you might base the query on pg_attribute:
SELECT attname AS column_name, format_type(atttypid, atttypmod) AS data_type
FROM pg_attribute
WHERE attrelid = 'public.view_name'::regclass
-- AND NOT attisdropped
-- AND attnum > 0
ORDER BY attnum;
Type modifiers like maximum length are included in data_type this way.
Internally, a VIEW is implemented as special table with a rewrite rule. Details in the manual here. The table is saved in the system catalogs much like any regular table.
About the cast to regclass:
How to check if a table exists in a given schema
The same query works for tables or materialized views as well. Uncomment the additional filters above to only get visible user columns for tables.
SELECT
a.attname,
t.typname,
a.atttypmod
FROM pg_class c
INNER JOIN pg_attribute a ON a.attrelid = c.oid
INNER JOIN pg_type t ON t.oid = a.atttypid
WHERE c.relkind = 'v'
AND c.relname = 'put_viewname_here';
ATTENTION: Since the viewname is unique only in the schema, you might also want to add an INNER JOIN to pg_namespace and add a condition to the where-clause.
For the first version of your question:
SELECT n.nspname
FROM pg_class c
INNER JOIN pg_namespace n ON n.oid = c.relnamespace
WHERE c.relkind = 'v'
AND c.relname = 'put_viewname_here';
ATTENTION: This might give you multiple schemas, since a viewname is only unique inside a schema and thus a viewname does not always identify one view.
I have a Firebird query which I should rewrite into PostgreSQL code.
SELECT TRIM(RL.RDB$RELATION_NAME), TRIM(FR.RDB$FIELD_NAME), FS.RDB$FIELD_TYPE
FROM RDB$RELATIONS RL
LEFT OUTER JOIN RDB$RELATION_FIELDS FR ON FR.RDB$RELATION_NAME = RL.RDB$RELATION_NAME
LEFT OUTER JOIN RDB$FIELDS FS ON FS.RDB$FIELD_NAME = FR.RDB$FIELD_SOURCE
WHERE (RL.RDB$VIEW_BLR IS NULL)
ORDER BY RL.RDB$RELATION_NAME, FR.RDB$FIELD_NAME
I understand SQL, but have no idea, how to work with this system tables like RDB$RELATIONS etc. It would be really great if someone helped me with this, but even some links with this tables explanation will be OK.
This piece of query is in C++ code, and when I'm trying to do this :
pqxx::connection conn(serverAddress.str());
pqxx::work trans(conn);
pqxx::result res(trans.exec(/*there is this SQL query*/));//and there is a mistake
it writes that:
RDB$RELATIONS doesn't exist.
Postgres has another way of storing information about system content. This is called System Catalogs.
In Firebird your query basically returns a row for every column of a table in every schema with an additional Integer column that maps to a field datatype.
In Postgres using system tables in pg_catalog schema something similar can be achieved using this query:
SELECT
TRIM(c.relname) AS table_name, TRIM(a.attname) AS column_name, a.atttypid AS field_type
FROM pg_class c
LEFT JOIN pg_attribute a ON
c.oid = a.attrelid
AND a.attnum > 0 -- only ordinary columns, without system ones
WHERE c.relkind = 'r' -- only tables
ORDER BY 1,2
Above query does return system catalogs as well. If you'd like to exclude them you need to add another JOIN to pg_namespace and a where clause with pg_namespace.nspname <> 'pg_catalog', because this is the schema where system catalogs are stored.
If you'd also like to see datatype names instead of their representative numbers add a JOIN to pg_type.
Information schema consists of collection of views. In most cases you don't need the entire SQL query that stands behind the view, so using system tables will give you better performance. You can inspect views definition though, just to get you started on the tables and conditions used to form an output.
I think you are looking for the information_schema.
The tables are listed here: https://www.postgresql.org/docs/current/static/information-schema.html
So for example you can use:
select * from information_schema.tables;
select * from information_schema.columns;
I'm aware of the psql command that will list these, but I'm attempting to write an extension for Oracle's SQL Developer that will list them on the left-hand navigator panel. The XML format requires a select statement.
For example purposes, I'll include the code I cooked up for sequences:
<sql constrained="true">
<![CDATA[SELECT relname FROM pg_class JOIN pg_namespace ON pg_namespace.oid = pg_class.relnamespace WHERE relkind = 'S' AND nspname = :SCHEMA]]>
</sql>
I've attempted to figure it out for myself, but I don't see anything with my test domain names in pg_class or any other of those internal tables (though it must be in one, somewhere).
Does anyone have a hint?
Asked too soon... here's a select query that will return domains from a specific schema:
SELECT typname FROM pg_catalog.pg_type JOIN pg_catalog.pg_namespace ON pg_namespace.oid = pg_type.typnamespace WHERE typtype = 'd' AND nspname = 'someschema'
Minor tweaking can also return enums, ranges, and composites/rows. More information in the docs.
I want to find all objects (tables, views, ... etc) that have a dependency on a specific table.
What is a query I could write in postgres to accomplish this.
You'd need to query the catalog for that. Probably pg_depend:
http://www.postgresql.org/docs/current/static/catalog-pg-depend.html
Incase you ever need it, don't miss the convenience type converter that lets you turn table oids and text into relnames like so:
select 'pg_statistics'::regclass; -- 'pg_statistics'
select 2619::regclass; -- 'pg_statistics' too, on my install
# select refclassid::regclass from pg_depend where classid = 'pg_class'::regclass group by refclassid;
refclassid
--------------
pg_namespace
pg_type
pg_class