Could you tell me how to check what indexes are created for some table in postgresql ?
The view pg_indexes provides access to useful information about each index in the database, eg.
select *
from pg_indexes
where tablename not like 'pg%';
if you're in psql, then:
\d tablename
show Indexes, Foreign Keys and references...
You can use this query:
select tablename,indexname,tablespace,indexdef from pg_indexes where tablename = 'your_table_name';
where has tablename is a field in pg_indexes ,you an get an accurate indices by matching user defined table at 'your_table_name' at WHERE clause . This will give you the desired details.
You can find all the index related information inside the pg_indexes view. Sometimes, a table may be part of some schema ("owner") or might have had a different name in the past (see: PostgreSQL Rename Table).
So first find out what is the schema ("owner") of the table:
SELECT schemaname, tablename FROM pg_tables WHERE tablename='table_name';
and then query indexes on the table with either of these queries:
SELECT tablename, indexname FROM pg_indexes WHERE tablename='table_name';
-- or
SELECT * FROM pg_indexes WHERE tablename='schema_name.table_name';
As an alternative to all the above, you can also use \d:
\d table_name;
The command
\di
will list all indexes for the current schema.
Related
I am using Postgres 12 in Docker in development.
In my project the primary key using UUID, and when I logged into the pgsql console, and try to setup indices for better performance.
When executing a select on pg_indexes table, it shows all indexes related to our tables.
SELECT
tablename,
indexname,
indexdef
FROM
pg_indexes
WHERE
schemaname = 'public'
ORDER BY
tablename,
indexname;
But when I used \d tablename to show the table info, it only show the table structure, no other information.
try to off the tuple only mode by \t
then run \d tablename
I am trying to query the constraint clauses along with schema and table in postgres. I've gotten as far as identifying information_schema.check_constraints as a useful table. The problem is that doing
select *
from information_schema.check_constraints
Results in constraint_catalog, constraint_schema, constraint_name, check_clause. The check_clause is what I want and this table also gives me the constraint_schema. However, it does not give the table that this constraint is defined on. In my current database, I have constraints with the same name defined on different tables within the same schema (which is in it of itself perhaps poor design but what I need to deal with). Is it possible to get the table name here as well?
select
conname,
connamespace::regnamespace as schemaname,
conrelid::regclass as tablename,
consrc as checkclause,
pg_get_constraintdef(oid) as definition
from
pg_constraint
where
contype = 'c'
and conrelid <> 0; -- to get only table constraints
About pg_constraint
About Object Identifier Types
I want to check column values of a specific table, but forgot the tablename. I only have the column names. What can I do?
I remember that I can get the tablenames from the DB2 catalog with:
select tabname from syscat.tables
What is the query to retrieve the tables related to a particular column in DB2?
The following should do:
select tabschema, tabname
from syscat.columns
where colname='myColumnOfInterest'
The column metadata is stored in SYSCAT.COLUMNS.
In DB2 for i
SELECT TABLE_NAME, SYSTEM_TABLE_NAME, COLUMN_NAME, SYSTEM_COLUMN_NAME
FROM QSYS2/SYSCOLUMNS
WHERE COLUMN_NAME = 'YOUCOLUMNAME' AND TABLE_SCHEMA = 'YOURLIB'
I have a PostgreSQL database table with 4 columns - labeled column_a, column_b, etc. I want to query this table with a simple select query:
select * from table_name;
I get a handful of results looking like:
column_a | column_b
---------+---------
'a value'|'b_value'
But when I use this query:
select * from schema_name.table_name;
I get the full result:
column_a | column_b | column_c | column_d
---------+----------+----------+---------
'a value'|'b value' |'c value' |'d_value'
Columns c and d were added at a later date, after initial table creation. My question is: Why would the database ignore the later columns when the schema name is left out of the select query?
Table names are not unique within a database in Postgres. There can be any number of tables named 'table_name' in different schemas - including the temporary schema, which always comes first unless you explicitly list it after other schemas in the search_path. Obviously, there are multiple tables named table_name. You must understand the role of the search_path to interpret this correctly:
How does the search_path influence identifier resolution and the "current schema"
The first table lives in a schema that comes before schema_name in your search_path (or schema_name is not listed there at all). So the unqualified table name is resolved to this table (or view). Check the list of tables named 'table_name' that your current role has access to in your database:
SELECT *
FROM information_schema.tables
WHERE table_name = 'table_name';
Views are just special tables with an attached RULE internally. They could play the same role as a regular table and are included in the above query.
Details:
How to check if a table exists in a given schema
Does anyone know how to find the OID of a table in Postgres 9.1?
I am writing an update script that needs to test for the existence of a column in a table before it tries to add the column. This is to prevent errors when running the script repeatedly.
To get a table OID, cast to the object identifier type regclass (while connected to the same DB):
SELECT 'mytbl'::regclass::oid;
This finds the first table (or view, etc.) with the given name along the search_path or raises an exception if not found.
Schema-qualify the table name to remove the dependency on the search path:
SELECT 'myschema.mytbl'::regclass::oid;
In Postgres 9.4 or later you can also use to_regclass('myschema.mytbl'), which doesn't raise an exception if the table is not found:
How to check if a table exists in a given schema
Then you only need to query the catalog table pg_attribute for the existence of the column:
SELECT TRUE AS col_exists
FROM pg_attribute
WHERE attrelid = 'myschema.mytbl'::regclass
AND attname = 'mycol'
AND NOT attisdropped -- no dropped (dead) columns
-- AND attnum > 0 -- no system columns (you may or may not want this)
;
The postgres catalog table pg_class is what you should look at. There should be one row per table, with the table name in the column relname, and the oid in the hidden column oid.
You may also be interested in the pg_attribute catalog table, which includes one row per table column.
See: http://www.postgresql.org/docs/current/static/catalog-pg-class.html and http://www.postgresql.org/docs/current/static/catalog-pg-attribute.html
SELECT oid FROM pg_class WHERE relname = 'tbl_name' AND relkind = 'r';
Just to complete the possibilities I'd like to add that there exists a syntax for dropping columns in order to no error out:
ALTER TABLE mytbl
DROP COLUMN IF EXISTS mycol
See http://www.postgresql.org/docs/9.0/static/sql-altertable.html
Then you can safely add your column.