how would the query on:
Update the field total_horas with the hours worked on each project
I have:
insert into proyecto(total_horas)
select trabaja.nhoras
from trabaja;
But it's trying to insert in the first firld of "proyecto" instead on the field "total_horas"
my table:
CREATE TABLE proyecto (
cdpro CHAR(3) NOT NULL PRIMARY KEY,
nombre VARCHAR(30),
coddep CHAR(2),
FOREIGN KEY (coddep)
REFERENCES departamento(cddep)
ON DELETE CASCADE
);
also altered with: alter table proyecto ADD total_horas char ;
You have to put a where condition in select statement.And please elaborate you question. trabaja.nhoras is the column name and you are selecting it from table trabaja
Example:
INSERT INTO proyecto
(total_horas)
SELECT trabaja.nhoras
FROM trabaja
WHERE 'condition' = 'some condition';
Related
I have these three tables in postgres database:
create table staff (
e_id int primary key,
first_name text,
last_name text,
job text,
branch_name text);
create table temp_staff (
t_id int primary key,
t_first_name text,
t_last_name text,
t_job text );
create table replacements(
e_id int ,
t_id int,
from_date date,
until_date date,
primary key(e_id, t_id, from_date) );
Now I want to add a constraint to the replacements table so you can insert a replacement with e_id and t_id only if e_id exists in the staff table and t_id exists in the temp_staff table.
I tried this:
alter table replacements
add constraint check_existence
check(exists (select 1 from staff where e_id = e_id) and exists (select 1 from temp_staff where t_id = t_id));
And got the error:
ERROR: cannot use subquery in check constraint
Thanks in advance for any help.
Is it not supposed to delete null values before altering the table? I'm confused...
My query looks roughly like this:
BEGIN;
DELETE FROM my_table
WHERE my_column IS NULL;
ALTER TABLE my_table DROP CONSTRAINT my_table_pk;
ALTER TABLE my_table ADD PRIMARY KEY (id, my_column);
-- this is to repopulate the data afterwards
INSERT INTO my_table (name, other_table_id, my_column)
SELECT
ya.name,
ot.id,
my_column
FROM other_table ot
LEFT JOIN yet_another ya
ON ya.id = ot."fileId"
WHERE NOT EXISTS (
SELECT
1
FROM my_table mt
WHERE ot.id = mt.other_table_id AND ot.my_column = mt.my_column
) AND my_column IS NOT NULL;
COMMIT;
sorry for naming
There are two possible explanations:
A concurrent session inserted a new row with a NULL value between the start of the DELETE and the start of ALTER TABLE.
To avoid that, lock the table in SHARE mode before you DELETE.
There is a row where id has a NULL value.
I'm trying to use the performance of COPY FROM command in PostgreSQL to get all data of 1 table of a CSV file (CSV -> table1) and I need to insert other data, but, in a new table. I will need of a primary key of first table to put as a foreign key in second table.
Example:
I need to insert 1,000,000 of names in table1 and 500,000 of names in table2, but, all names in table2 reference to 1 tuple in table1.
CREATE TABLE table1 (
table1Id bigserial NOT NULL,
Name varchar(100) NULL,
CONSTRAINT table1Id PRIMARY KEY (table1Id)
);
CREATE TABLE table2 (
table2Id bigserial NOT NULL,
Other_name varchar(100) NOT NULL
table1_table1Id int8 NOT NULL,
CONSTRAINT table2_pk PRIMARY KEY (table2Id)
);
Command COPY does not allow table manipulations while copying data (such as look up to other table for fetching proper foreign keys to insert). To insert into table2 ids for corresponding rows from table1 you need to drop NOT NULL constraint for that field, COPY data and then UPDATE that fields separately.
Assuming table1 and table2 tables can be joined by table1.Name = table2.Other_name, the code is:
Before COPY:
ALTER TABLE table2 ALTER COLUMN table1_table1Id DROP NOT NULL;
After COPY:
UPDATE table2 SET table2.table1_table1Id = table1.table1Id
FROM table1
WHERE table1.Name = table2.Other_name;
ALTER TABLE table2 ALTER COLUMN table1_table1Id SET NOT NULL;
I'm still a newbie.
I created db like this :
DROP DATABASE IF EXISTS image_store_db;
CREATE DATABASE image_store_db;
\c image_store_db;
CREATE TABLE categories_images (
categories_images_id SERIAL PRIMARY KEY,
title VARCHAR NOT NULL,
image_url VARCHAR NOT NULL,
design_url VARCHAR NOT NULL
);
CREATE TABLE images (
images_id SERIAL PRIMARY KEY,
title VARCHAR NOT NULL,
rating REAL NOT NULL,
image_url VARCHAR NOT NULL,
desc_short TEXT NOT NULL,
desc_full TEXT NOT NULL
);
CREATE TABLE ref_categories_images (
categories_images_id integer REFERENCES categories_images (categories_images_id) ON UPDATE CASCADE,
images_id integer REFERENCES images (images_id) ON UPDATE CASCADE ON DELETE CASCADE,
CONSTRAINT ref_categories_images_pkey PRIMARY KEY (images_id, categories_images_id)
);
INSERT INTO categories_images(title, image_url, design_url)
VALUES ('SIMPLE TITLE TEST', '/TEST_URL.PNG', '/TEST_URL.PNG');
INSERT INTO images(title, rating, image_url, desc_short, desc_full)
VALUES ('SIMPLE TITLE TEST', 4.5, '/TEST_URL.PNG', 'TEST_SHORT', 'TEST_FULL');
Pls, help. Teach me, how write a query : insert (for image in category) and select (image from category id) and etc ...
pls ...
My answer assumes that categories_images is the table of categories and images is the table of images. The table and attribute names seem to suggest that the concept of many-to-many join is not all clear to you yet; I would have called the three tables category, image and category_image_map.
For INSERT: if your problem are the serial primary keys, use INSERT ... RETURNING.
You can insert into all three tables in a single statement:
WITH im(im_id) AS (
INSERT INTO categories_images ...
RETURNING categories_images_id
),
cat(cat_id) AS (
INSERT INTO images ...
RETURNING images_id
)
INSERT INTO ref_categories_images (categories_images_id, images_id)
VALUES ((SELECT cat_id FROM cat), (SELECT im_id FROM im));
For the query, you just join the three tables:
SELECT ...
FROM categories_images c
JOIN ref_categories_images r
ON r.categories_images_id = c.categories_images_id
JOIN images i
ON r.images_id = i.images_id
and add a WHERE clause for your condition, for example
WHERE c.categories_images_id = 42
or
WHERE i.image_title = 'Mona Lisa'
To create table I use:
CREATE TABLE category
(
cat_id serial NOT NULL,
cat_name character varying NOT NULL,
parent_id integer NOT NULL,
CONSTRAINT cat_id PRIMARY KEY (cat_id)
)
WITH (
OIDS=FALSE
);
ALTER TABLE category
OWNER TO pgsql;
parent_id is a id to another category. Now I have a problem: how to cascade delete record with its children? I need to set parent_id as foreign key to cat_id.
I try this:
ALTER TABLE category
ADD CONSTRAINT cat_cat_id_fkey FOREIGN KEY (parent_id)
REFERENCES category (cat_id) MATCH SIMPLE
ON UPDATE CASCADE ON DELETE CASCADE
But it falls with:
ERROR: insert or update on table "category" violates foreign key constraint "cat_cat_id_fkey"
DETAIL: Key (parent_id)=(0) is not present in table "category".
The problem you have - what would be the parent_id of a category at the top of the hierarchy?
If it will be null - it will break the NOT NULL constratint.
If it will be some arbitrary number like 0 - it will break the foreign key (like in your example).
The common solution - drop the NOT NULL constratint on the parent_id and set parent_id to null for top categories.
-- create some fake data for testing
--
DROP SCHEMA tmp CASCADE;
CREATE SCHEMA tmp ;
SET search_path=tmp;
CREATE TABLE category
(
cat_id serial NOT NULL,
cat_name character varying NOT NULL,
parent_id integer NOT NULL,
CONSTRAINT cat_id PRIMARY KEY (cat_id)
);
INSERT INTO category(cat_name,parent_id)
SELECT 'Name_' || gs::text
, gs % 3
FROM generate_series(0,9) gs
;
-- find the records with the non-existing parents
SELECT ca.parent_id , COUNT(*)
FROM category ca
WHERE NOT EXISTS (
SELECT *
FROM category nx
WHERE nx.cat_id = ca.parent_id
)
GROUP BY ca.parent_id
;
-- if all is well: proceed
-- make parent pointer nullable
ALTER TABLE category
ALTER COLUMN parent_id DROP NOT NULL
;
-- set non-existing parent pointers to NULL
UPDATE category ca
SET parent_id = NULL
WHERE NOT EXISTS (
SELECT *
FROM category nx
WHERE nx.cat_id = ca.parent_id
)
;
-- Finally, add the FK constraint
ALTER TABLE category
ADD CONSTRAINT cat_cat_id_fkey FOREIGN KEY (parent_id)
REFERENCES category (cat_id) MATCH SIMPLE
ON UPDATE CASCADE ON DELETE CASCADE
;
This is quite simple.
Here the foreign key parent_id refers to cat_id.
Here a record with parent_id=0 exists but not a record with cat_id=0.