I logged into my postgresql database in a cloud server, and I know that \d is used for showing all tables in my database, and \d mytablename is used for showing all columns in the table.
However, can anyone tell me how to show the contents of each column in the table?
I have tried to use SELECT * FROM mytablename, but it does not make any difference.
Related
I have create a redshift cluster and created a db inside.
My schema is new_schema
I have created 2 tables inside two tables inside table1, table2
My Question.
I want to list the datatypes of table1
I need to change the datatype of description which is inside the table1 which is of VARCHAR to TEXT
I have tried to list the datatypes of table1 with below query but nothing listing
SELECT * FROM PG_TABLE_DEF WHERE schemaname = 'new_schema';
A few possibilities as to why you are not seeing the expected results. Most likely is that new_schema isn't in your search_path. Pg_table_info only return info for tables in your search_path - see: https://docs.aws.amazon.com/redshift/latest/dg/r_PG_TABLE_DEF.html
Another possibility is that the tables have no data rows (no blocks assigned) and this can lead to incomplete info from some system tables.
Another possibility is that the tables were not committed by the creating session and being checked by a different session. Since you say that you are creating a new db this comes to mind.
Are the tables visible in svv_table_info?
Also the premise of changing varchar to text is a bit off. From https://docs.aws.amazon.com/redshift/latest/dg/r_Character_types.html#r_Character_types-text-and-bpchar-types
You can create an Amazon Redshift table with a TEXT column, but it is
converted to a VARCHAR(256) column that accepts variable-length values
with a maximum of 256 characters.
So it seems like the objective you are trying to achieve is a bit off.
On Google Data Studio, I cannot create a chart from Postgres data if table columns are in camelCase. I have data in PostgreSQL where I want to get charts from. Integrating it as a data source works fine. Now, I have a problem when creating a chart.
After creating a chart and selecting a data source, I try to add a column, which results in this error:
Error with SQL statement: ERROR: column "columnname" does not exist Hint: Perhaps you meant to reference the column "table.columnName". Position: 8
It just so happens that all my columns are in camelCase. Is there no way around this? Surely this is a basic question that has been resolved.
When connecting to your data source, try using 'Custom query' instead of selecting a table from your database. Then manually write your SQL query where you cast your camel case column names to lower case using sql alias. Worked for me.
example:
SELECT
"camelCaseColA" as cola,
"camelCaseColB" as colb,
"camelCaseColC" as colc
FROM
tableName as table
I have many tables in different databases and want to bring them to a database.
It seems like I have to create foreign table in the database (where I want to merge them all) with schemas of all the tables.
I am sure, there is a way to automate this (by the way, I am going to use psql command) but I do not know where to start.
what I have found so far is I can use
select * from information_schema.columns
where table_schema = 'public' and table_name = 'mytable'
I added more detail explanation.
I wanted to copy tables from another database
the tables have same column names and data type
using postgres_fdw, I needed to set up a field name and data type for each tables (the table names are also same)
then, I want to union the tables have same name all to have one single table.
for that, I am going to add prefix on table
for instance, mytable in db1, mytable in db2, mytable in db3 as in
db1_mytable, db2_mytable, db3_mytable in my local database.
Thanks to Albe's comment, I managed it and now I need to figure out doing 4th step using psql command.
i want to create a simple table inside a database in postgresql.
From the Documentation i have CREATE TABLE will create a new, initially empty table in the current database. The table will be owned by the user issuing the command.
With this command
CREATE TABLE *table_name*;
I thought i get a new empty table.But psql throws ERROR: syntax error at or near ";". When i user an empty argument list like:
CREATE TABLE *table_name*();
psql tells me that the table was created through
postgres=# create table *table_name*();
CREATE TABLE
But \l shows is not showing the newly created table. And its also not possible to login with psql -d table_name -U user_name. Can anyone help?
You can have a table with no columns, and even with some rows in it:
CREATE TABLE nocolumn (dummy INTEGER NOT NULL PRIMARY KEY)
;
INSERT INTO nocolumn(dummy) VALUES (1);
ALTER TABLE nocolumn
DROP COLUMN dummy;
\d nocolumn
SELECT COUNT(*) FROM nocolumn;
Output:
CREATE TABLE
INSERT 0 1
ALTER TABLE
Table "tmp.nocolumn"
Column | Type | Modifiers
--------+------+-----------
count
-------
1
(1 row)
You seem to be confusing the terms database and table
But \l is not showing the newly created table.
Of course \l will not show you that table, because \l will list databases not relations. To see all tables you need to use \d or \dt.
And its also not possible to login with psql -d table_name -U user_name
Of course this is not possible, because the -d parameter is used to specify a database, not a table
I'm not sure why other answers suggest to create a table with a column and then ignore that column. It is certainly possible, but it seems different from what you tried to do.
It seems you have to use parenthesis:
postgres=# CREATE TABLE t ();
CREATE TABLE
To insert a row:
postgres=# INSERT INTO t DEFAULT VALUES;
INSERT 0 1
To count the rows you inserted:
postgres=# SELECT FROM t;
--
(2 rows)
You can't delete a single rows, because all rows are equal. But to completely empty the table, you can use DELETE without WHERE, or TRUNCATE TABLE.
You can find more info here: PostgreSQL: Tables without columns.
That said, I have to say that I understand "empty table" as "table without rows", not necessarily without columns.
An hour ago i suggested to add at least one column like this:
create table tab1 (columnname varchar(42) not null)
But this seems to be not necessary as a commentator just told. (I consider to keep the wrong answer here instead of deleting it, to prevent that others suggest the same)
I am developing a windows application and using Postgres as backend database. At some point in my application i am dynamically creating table e.g Table1, then Table2 and so on. In this way i have many dynamic table in my database. Now i provide a button "Clean Database", so i need to remove all those dynamic tables using SQL query. Should some one guide me how to write SQL Query that automatically delete all such tables?
You should just be able to say
DROP TABLE {tablename}
for each dynamically created table. Try that and see if it works.