For example, there is a table named 'testtable' that has following columns: testint (integer) and testtext (varchar(30)).
What i want to do is pretty much something like that:
INSERT INTO testtable VALUES(15, CONTENT_OF_FILE('file'));
While reading postgresql documentation, all I could find is COPY TO/FROM command, but that one's applied to tables, not single columns.
So, what shall I do?
If this SQL code is executed dynamically from your programming language, use the means of that language to read the file, and execute a plain INSERT statement.
However, if this SQL code is meant to be executed via the psql command line tool, you can use the following construct:
\set content `cat file`
INSERT INTO testtable VALUES(15, :'content');
Note that this syntax is specific to psql and makes use of the cat shell command.
It is explained in detail in the PostgreSQL manual:
psql / SQL Interpolation
psql / Meta-Commands
If I understand your question correctly, you could read the single string(s) into a temp table and use that for insert:
DROP SCHEMA str CASCADE;
CREATE SCHEMA str;
SET search_path='str';
CREATE TABLE strings
( string_id INTEGER PRIMARY KEY
, the_string varchar
);
CREATE TEMP TABLE string_only
( the_string varchar
);
COPY string_only(the_string)
FROM '/tmp/string'
;
INSERT INTO strings(string_id,the_string)
SELECT 5, t.the_string
FROM string_only t
;
SELECT * FROM strings;
Result:
NOTICE: drop cascades to table str.strings
DROP SCHEMA
CREATE SCHEMA
SET
NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "strings_pkey" for table "strings"
CREATE TABLE
CREATE TABLE
COPY 1
INSERT 0 1
string_id | the_string
-----------+---------------------
5 | this is the content
(1 row)
Please note that the file is "seen" by the server as the server sees the filesystem. The "current directory" from that point of view is probably $PG_DATA, but you should assume nothing, and specify the complete pathname, which should be reacheable and readable by the server. That is why I used '/tmp', which is unsafe (but an excellent rendez-vous point ;-)
Related
I'm coming from a background in SQL Server where I would create temp tables using the:
select id
into #test
from table A
I've just moved into a PostGresql environment and I was hoping I could do the same, but I'm getting a syntax error. I did a search and it seems like you have to do a Create Table statement.
Is it not possible to easily create temp tables in Postgres?
Postgres supports SELECT INTO, so this should work fine:
SELECT id
INTO TEMP TABLE test
FROM a
You can also use CREATE TABLE AS:
CREATE TEMP TABLE test AS
SELECT id FROM a
This version is generally preferred, as the CREATE statement provides additional options, and can also be used in PL/pgSQL functions (where the SELECT INTO syntax has been hijacked for variable assignment).
Whenever a execute a query such as :
CREATE TABLE myTable (myColumn INTEGER);
PostgreSQL automatically converts the Table and Column names to lowercase like this:
CREATE TABLE mytable (mycolumn INTEGER);
Is there any way to change the source code of PostgreSQL to avoid this automatic change?
I know the Double Quote method... But...
The Application I'm using is very large. So it is very difficult to change every occurrence of the query. Instead, I would like to change the source code of PostgreSQL which is found on GitHub.
You can use double quotes:
CREATE TABLE "myTable" ("myColumn" INTEGER);
Is there a way to COPY the CSV file data directly into a JSON or JSONb array?
Example:
CREATE TABLE mytable (
id serial PRIMARY KEY,
info jSONb -- or JSON
);
COPY mytable(info) FROM '/tmp/myfile.csv' HEADER csv;
NOTE: each CSV line is mapped to a JSON array. It is a normal CSV.
Normal CSV (no JSON-embeded)... /tmp/myfile.csv =
a,b,c
100,Mum,Dad
200,Hello,Bye
The correct COPY command must be equivalent to the usual copy bellow.
Usual COPY (ugly but works fine)
CREATE TEMPORARY TABLE temp1 (
a int, b text, c text
);
COPY temp1(a,b,c) FROM '/tmp/myfile.csv' HEADER csv;
INSERT INTO mytable(info) SELECT json_build_array(a,b,c) FROM temp1;
It is ugly because:
need the a priory knowledge about fields, and a previous CREATE TABLE with it.
for "big data" need a big temporary table, so lost CPU, disk and my time — the table mytable have CHECKs and UNIQUEs constraints for each line.
... Needs more than 1 SQL command.
Perfect solution!
Not need to know all the CSV columns, only extract what you know.
Use at SQL CREATE EXTENSION PLpythonU;: if the command produce an error like "could not open extension control file ... No such file" you need to install pg-py extra-packages. In standard UBUNTU (16 LTS) is simple, apt install postgresql-contrib postgresql-plpython.
CREATE FUNCTION get_csvfile(
file text,
delim_char char(1) = ',',
quote_char char(1) = '"')
returns setof text[] stable language plpythonu as $$
import csv
return csv.reader(
open(file, 'rb'),
quotechar=quote_char,
delimiter=delim_char,
skipinitialspace=True,
escapechar='\\'
)
$$;
INSERT INTO mytable(info)
SELECT jsonb_build_array(c[1],c[2],c[3])
FROM get_csvfile('/tmp/myfile1.csv') c;
The split_csv() function was defined here. The csv.reader is very reliable (!).
Not tested for big-big CSV... But expected Python do job.
PostgreSQL workaround
It is not a perfect solution, but it solves the main problem, that is the
... big temporary table, so lost CPU, disk and my time"...
This is the way we do it, a workaround with file_fdw!
Adopt your conventions to avoid file-copy and file-permission confusions... The standard file path for a CSV. Example: /tmp/pg_myPrj_file.csv
Initialise your database or SQL script with the magic extension,
CREATE EXTENSION file_fdw;
CREATE SERVER files FOREIGN DATA WRAPPER file_fdw;
For each CSV file, myNewData.csv,
3.1. make a symbolic link (or scp remote copy) for your new file ln -sf $PWD/myNewData.csv /tmp/pg_socKer_file.csv
3.2. configure the file_fdw for your new table (suppose mytable).
CREATE FOREIGN TABLE temp1 (a int, b text, c text)
SERVER files OPTIONS (
filename '/tmp/pg_socKer_file.csv',
format 'csv',
header 'true'
);
PS: after running SQL script with psql, when having some permission problem, change owner of the link by sudo chown -h postgres:postgres /tmp/pg_socKer_file.csv.
3.3. use the file_fdw table as source (suppose populating mytable).
INSERT INTO mytable(info)
SELECT json_build_array(a,b,c) FROM temp1;
Thanks to #JosMac (and his tutorial)!
NOTE: if there is a STDIN way to do it (exists??), will be easy, avoiding permission problems and use of absolute paths. See this answer/discussion.
I've used the psql module to create a new database using the following syntax:
CREATE DATABASE fish
I can open the database. However, when I try to create tables or columns it gives me a syntax error for the following message.
CREATE TABLE salmon;
this is the error message:
ERROR: syntax error at or near ";"
LINE 1: CREATE TABLE species;
I've checked a lot of online postgreSQL resources and they haven't been of much help. To the best of my knowledge, I haven't messed up the syntax. Thanks.
you can use this syntax for empty table:
create table salmon();
You must create atleast one column in a table:
CREATE TABLE salmon ( column_name data_type ...........);
Postgres create table link: https://www.postgresql.org/docs/9.1/static/sql-createtable.html
You can't create an empty table - it must have at least one column. E.g.:
CREATE TABLE salmon (name VARCHAR(10));
psql is not a module. Please read https://www.postgresql.org/docs/current/static/app-psql.html
you odn't open a database - you connect to it.
Establishes a new connection to a PostgreSQL server
https://www.postgresql.org/docs/current/static/sql-createtable.html
{ column_name | ( expression ) }
Either column list (create table a (a int);) or expression (create table b as select now() time_column) is obligatory part.
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)