\d does not seem to work except for a table in PostgreSQL.
I want to be able to retrieve the equivalent of \d <table>, but for a SELECT query.
For example, I would like to say:
\d (SELECT statement) AS table2
where the SELECT statement might contain JOINs and so on
just like in TimesTen:
desc (SELECT .. FROM ... WHERE ...)
gives column info like name, type, and length
I can use \pset footer on or --expanded but it doesn't give data type and length.
Do you mind doing it inside a transaction?
begin;
create table x as select * from t with no data;
\d x
Table "public.x"
Column | Type | Modifiers
--------+-----------------------------+-----------
t | timestamp without time zone |
rollback;
Related
As school work we're supposed to create a table that logs all operations done by users on another table. To be more clear, say I have table1 and logtable, table1 can contain any info (names, ids, job, etc), logtable contains info on who did what, when on table1. Using a function and a trigger I managed to get the INSERT, DELETE and UPDATE operations to be a logged in logtable, but we're also supposed to keep a log of SELECTs. To be more specific about the SELECTs, in a View if you do a SELECT, this is supposed to be logged into logtable via an INSERT, essentially the logtable is supposed to have a new row with information telling that somebody did a SELECT. My problem is that I can't figure out any way to accomplish this as SELECTs can't make use of triggers and in turn can't make use of functions, and rules don't allow for two different operations to take place. The only thing that came close was using query logs, however as the database is the school's and not mine I can't make any use of them.
Here is a rough example of what I'm working with (in reality tstamp has hours minutes and such):
id operation hid tablename who tstamp val_new val_old
x INSERT x table1 name YYYY-MM-DD newValues previousValues
That works as intended, but what I also need to get to work is this (Note: Whether val_new and old come out as empty or not in this case is not a concern):
id operation hid tablename who tstamp val_new val_old
x SELECT x table1 name YYYY-MM-DD NULL previousValues
Any and all help is appreciated.
Here is an example:
CREATE TABLE public.test (id integer PRIMARY KEY, value integer);
INSERT INTO test VALUES (1,42),(2,13);
CREATE TABLE test_log(id serial primary key, dbuser varchar,datetime timestamp);
-- get_test() inserts username / timestamp into log, then returns all rows
-- of test
CREATE OR REPLACE FUNCTION get_test() RETURNS SETOF test AS '
INSERT INTO test_log (dbuser,datetime)VALUES(current_user,now());
SELECT * FROM test;'
language 'sql';
-- now a view returns the full row set of test by instead calling our function
CREATE VIEW test_v AS SELECT * FROM get_test();
SELECT * FROM test_v;
id | value
----+-------
1 | 42
2 | 13
(2 rows)
SELECT * FROM test_log;
id | dbuser | datetime
----+----------+----------------------------
1 | postgres | 2020-11-30 12:42:00.188341
(1 row)
If your table has many rows and/or the selects are complex, you don't want to use this view for performance reasons.
For a first time I find very handy way for importing "last year data" to "this year data".
This works well:
DROP TABLE IF EXISTS mytable;
CREATE TABLE mytable AS
SELECT col1, col2, col3, col4
FROM dblink('host=localhost port=xxxx user=xxxx password=xxxx dbname=mylastyeardb',
'SELECT col1, col2, col3, col4
FROM mytable
WHERE TRIM(col1)<>'''' ')
AS x(col1 text, col2 text, col3 text, col4 text);
ALTER TABLE mytable ADD COLUMN cols_id SERIAL PRIMARY KEY;
Since 'cols_id' from old table is not appropriate for a new table maybe some of experienced users know how to setup a table in CREATE TABLE AS that it have 'cols_id' as (serial) primary key nice ordered and as a first column. Maybe such way I can avoid using of second (ALTER) command?
Any other advice for showed situation will be welcome too.
you either create table, defining its structure (with all handy shortcuts and options in one statement), or create table as select, "inheriting" [partially] the structure. Thus if you want primary key, you will need alter tabale any way...
To put id as first column in one statement, you can simply use a dummy value, eg sequential number:
t=# create table s as select row_number() over() as id,chr(n) from generate_series(197,200) n;
SELECT 4
t=# select * from s;
id | chr
----+-----
1 | Å
2 | Æ
3 | Ç
4 | È
(4 rows)
Of course after that you still need to create sequence, assign its value as default to the id column and add primary key on ot. Which makes it even more statements then you have ATM...
I have a table with more than 20 columns, I want to get all columns except for one which I'll use in a conditional expression.
SELECT s.* (BUT NOT column1),
CASE WHEN column1 is null THEN 1 ELSE 2 END AS column1
from tb_sample s;
Can I achieve it in postgresql given the logic above?
It may not be ideal, but you can use information_schema to get the columns and use the column to exclude in the where clause.
That gives you a list of all the column names you DO want, which you can copy/paste into your select query:
select textcat(column_name, ',')
from information_schema.columns
where table_name ='table_name' and column_name !='column_to_exclude';
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
I am new to postgreSql and I used following query to retrieve all the fields from database.
SELECT student.*,row_number() OVER () as rnum FROM student;
I don't know how to delete particular row by row number.Please give me some idea.
This is my table:
Column | Type
------------+------------------
name | text
rollno | integer
cgpa | double precision
department | text
branch | text
with a as
(
SELECT student.*,row_number() OVER () as rnum FROM student
)
delete from student where ctid in (select ctid from a where rnum =1) -- the
-- row_number you want
-- to delete
Quoted from PostgreSQL - System Columns
ctid :
The physical location of the row version within its table. Note
that although the ctid can be used to locate the row version very
quickly, a row's ctid will change each time it is updated or moved by
VACUUM FULL. Therefore ctid is useless as a long-term row identifier.
The OID, or even better a user-defined serial number, should be used
to identify logical rows.
Note : I strongly recommend you to use an unique filed in student table.
As per Craig's comment, I'll give another way to solve OP's issue it's a bit tricky
First create a unique column for table student, for this use below query
alter table student add column stu_uniq serial
this will produce stu_uniq with corresponding unique values for each row, so that OP can easily DELETE any row(s) using this stu_uniq
I don't know whether its a correct alternative for this problem.But it satisfies my problem.What my problem is I need to delete a row without help of anyone of it's column.I created table with OIDS,and with help of oid I deleted the rows.
CREATE TABLE Student(Name Text,RollNo Integer,Cgpa Float,Department Text,Branch Text)WITH OIDS;
DELETE FROM STUDENT WHERE oid=18789;
DELETE FROM STUDENT WHERE oid=18790;
Quoted from PostgreSQL - System Columns
Thanks to #WingedPanther for suggesting this idea.
You could try like this.
create table t(id int,name varchar(10));
insert into t values(1,'a'),(2,'b'),(3,'c'),(4,'d');
with cte as
(
select *,ROW_NUMBER()over(order by id) as rn from t
)
delete from cte where rn=1;
Cte in Postgres