242 lines
9.3 KiB
Plaintext
242 lines
9.3 KiB
Plaintext
-- from http://www.depesz.com/index.php/2010/04/19/getting-unique-elements/
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CREATE TEMP TABLE articles (
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id int CONSTRAINT articles_pkey PRIMARY KEY,
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keywords text,
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title text UNIQUE NOT NULL,
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body text UNIQUE,
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created date
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);
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NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "articles_pkey" for table "articles"
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NOTICE: CREATE TABLE / UNIQUE will create implicit index "articles_title_key" for table "articles"
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NOTICE: CREATE TABLE / UNIQUE will create implicit index "articles_body_key" for table "articles"
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CREATE TEMP TABLE articles_in_category (
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article_id int,
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category_id int,
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changed date,
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PRIMARY KEY (article_id, category_id)
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);
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NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "articles_in_category_pkey" for table "articles_in_category"
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-- test functional dependencies based on primary keys/unique constraints
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-- base tables
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-- group by primary key (OK)
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SELECT id, keywords, title, body, created
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FROM articles
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GROUP BY id;
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id | keywords | title | body | created
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----+----------+-------+------+---------
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(0 rows)
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-- group by unique not null (fail/todo)
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SELECT id, keywords, title, body, created
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FROM articles
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GROUP BY title;
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ERROR: column "articles.id" must appear in the GROUP BY clause or be used in an aggregate function
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LINE 1: SELECT id, keywords, title, body, created
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^
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-- group by unique nullable (fail)
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SELECT id, keywords, title, body, created
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FROM articles
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GROUP BY body;
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ERROR: column "articles.id" must appear in the GROUP BY clause or be used in an aggregate function
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LINE 1: SELECT id, keywords, title, body, created
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^
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-- group by something else (fail)
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SELECT id, keywords, title, body, created
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FROM articles
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GROUP BY keywords;
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ERROR: column "articles.id" must appear in the GROUP BY clause or be used in an aggregate function
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LINE 1: SELECT id, keywords, title, body, created
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^
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-- multiple tables
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-- group by primary key (OK)
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SELECT a.id, a.keywords, a.title, a.body, a.created
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FROM articles AS a, articles_in_category AS aic
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WHERE a.id = aic.article_id AND aic.category_id in (14,62,70,53,138)
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GROUP BY a.id;
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id | keywords | title | body | created
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----+----------+-------+------+---------
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(0 rows)
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-- group by something else (fail)
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SELECT a.id, a.keywords, a.title, a.body, a.created
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FROM articles AS a, articles_in_category AS aic
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WHERE a.id = aic.article_id AND aic.category_id in (14,62,70,53,138)
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GROUP BY aic.article_id, aic.category_id;
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ERROR: column "a.id" must appear in the GROUP BY clause or be used in an aggregate function
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LINE 1: SELECT a.id, a.keywords, a.title, a.body, a.created
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^
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-- JOIN syntax
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-- group by left table's primary key (OK)
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SELECT a.id, a.keywords, a.title, a.body, a.created
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FROM articles AS a JOIN articles_in_category AS aic ON a.id = aic.article_id
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WHERE aic.category_id in (14,62,70,53,138)
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GROUP BY a.id;
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id | keywords | title | body | created
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----+----------+-------+------+---------
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(0 rows)
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-- group by something else (fail)
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SELECT a.id, a.keywords, a.title, a.body, a.created
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FROM articles AS a JOIN articles_in_category AS aic ON a.id = aic.article_id
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WHERE aic.category_id in (14,62,70,53,138)
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GROUP BY aic.article_id, aic.category_id;
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ERROR: column "a.id" must appear in the GROUP BY clause or be used in an aggregate function
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LINE 1: SELECT a.id, a.keywords, a.title, a.body, a.created
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^
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-- group by right table's (composite) primary key (OK)
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SELECT aic.changed
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FROM articles AS a JOIN articles_in_category AS aic ON a.id = aic.article_id
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WHERE aic.category_id in (14,62,70,53,138)
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GROUP BY aic.category_id, aic.article_id;
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changed
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---------
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(0 rows)
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-- group by right table's partial primary key (fail)
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SELECT aic.changed
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FROM articles AS a JOIN articles_in_category AS aic ON a.id = aic.article_id
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WHERE aic.category_id in (14,62,70,53,138)
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GROUP BY aic.article_id;
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ERROR: column "aic.changed" must appear in the GROUP BY clause or be used in an aggregate function
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LINE 1: SELECT aic.changed
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^
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-- example from documentation
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CREATE TEMP TABLE products (product_id int, name text, price numeric);
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CREATE TEMP TABLE sales (product_id int, units int);
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-- OK
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SELECT product_id, p.name, (sum(s.units) * p.price) AS sales
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FROM products p LEFT JOIN sales s USING (product_id)
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GROUP BY product_id, p.name, p.price;
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product_id | name | sales
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------------+------+-------
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(0 rows)
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-- fail
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SELECT product_id, p.name, (sum(s.units) * p.price) AS sales
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FROM products p LEFT JOIN sales s USING (product_id)
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GROUP BY product_id;
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ERROR: column "p.name" must appear in the GROUP BY clause or be used in an aggregate function
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LINE 1: SELECT product_id, p.name, (sum(s.units) * p.price) AS sales
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^
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ALTER TABLE products ADD PRIMARY KEY (product_id);
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NOTICE: ALTER TABLE / ADD PRIMARY KEY will create implicit index "products_pkey" for table "products"
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-- OK now
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SELECT product_id, p.name, (sum(s.units) * p.price) AS sales
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FROM products p LEFT JOIN sales s USING (product_id)
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GROUP BY product_id;
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product_id | name | sales
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------------+------+-------
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(0 rows)
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-- Drupal example, http://drupal.org/node/555530
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CREATE TEMP TABLE node (
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nid SERIAL,
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vid integer NOT NULL default '0',
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type varchar(32) NOT NULL default '',
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title varchar(128) NOT NULL default '',
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uid integer NOT NULL default '0',
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status integer NOT NULL default '1',
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created integer NOT NULL default '0',
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-- snip
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PRIMARY KEY (nid, vid)
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);
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NOTICE: CREATE TABLE will create implicit sequence "node_nid_seq" for serial column "node.nid"
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NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "node_pkey" for table "node"
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CREATE TEMP TABLE users (
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uid integer NOT NULL default '0',
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name varchar(60) NOT NULL default '',
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pass varchar(32) NOT NULL default '',
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-- snip
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PRIMARY KEY (uid),
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UNIQUE (name)
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);
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NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "users_pkey" for table "users"
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NOTICE: CREATE TABLE / UNIQUE will create implicit index "users_name_key" for table "users"
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-- OK
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SELECT u.uid, u.name FROM node n
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INNER JOIN users u ON u.uid = n.uid
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WHERE n.type = 'blog' AND n.status = 1
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GROUP BY u.uid, u.name;
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uid | name
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-----+------
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(0 rows)
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-- OK
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SELECT u.uid, u.name FROM node n
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INNER JOIN users u ON u.uid = n.uid
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WHERE n.type = 'blog' AND n.status = 1
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GROUP BY u.uid;
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uid | name
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-----+------
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(0 rows)
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-- Check views and dependencies
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-- fail
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CREATE TEMP VIEW fdv1 AS
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SELECT id, keywords, title, body, created
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FROM articles
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GROUP BY body;
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ERROR: column "articles.id" must appear in the GROUP BY clause or be used in an aggregate function
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LINE 2: SELECT id, keywords, title, body, created
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^
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-- OK
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CREATE TEMP VIEW fdv1 AS
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SELECT id, keywords, title, body, created
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FROM articles
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GROUP BY id;
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-- fail
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ALTER TABLE articles DROP CONSTRAINT articles_pkey RESTRICT;
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ERROR: cannot drop constraint articles_pkey on table articles because other objects depend on it
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DETAIL: view fdv1 depends on constraint articles_pkey on table articles
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HINT: Use DROP ... CASCADE to drop the dependent objects too.
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DROP VIEW fdv1;
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-- multiple dependencies
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CREATE TEMP VIEW fdv2 AS
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SELECT a.id, a.keywords, a.title, aic.category_id, aic.changed
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FROM articles AS a JOIN articles_in_category AS aic ON a.id = aic.article_id
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WHERE aic.category_id in (14,62,70,53,138)
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GROUP BY a.id, aic.category_id, aic.article_id;
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ALTER TABLE articles DROP CONSTRAINT articles_pkey RESTRICT; -- fail
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ERROR: cannot drop constraint articles_pkey on table articles because other objects depend on it
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DETAIL: view fdv2 depends on constraint articles_pkey on table articles
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HINT: Use DROP ... CASCADE to drop the dependent objects too.
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ALTER TABLE articles_in_category DROP CONSTRAINT articles_in_category_pkey RESTRICT; --fail
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ERROR: cannot drop constraint articles_in_category_pkey on table articles_in_category because other objects depend on it
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DETAIL: view fdv2 depends on constraint articles_in_category_pkey on table articles_in_category
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HINT: Use DROP ... CASCADE to drop the dependent objects too.
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DROP VIEW fdv2;
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-- nested queries
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CREATE TEMP VIEW fdv3 AS
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SELECT id, keywords, title, body, created
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FROM articles
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GROUP BY id
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UNION
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SELECT id, keywords, title, body, created
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FROM articles
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GROUP BY id;
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ALTER TABLE articles DROP CONSTRAINT articles_pkey RESTRICT; -- fail
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ERROR: cannot drop constraint articles_pkey on table articles because other objects depend on it
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DETAIL: view fdv3 depends on constraint articles_pkey on table articles
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HINT: Use DROP ... CASCADE to drop the dependent objects too.
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DROP VIEW fdv3;
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CREATE TEMP VIEW fdv4 AS
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SELECT * FROM articles WHERE title IN (SELECT title FROM articles GROUP BY id);
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ALTER TABLE articles DROP CONSTRAINT articles_pkey RESTRICT; -- fail
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ERROR: cannot drop constraint articles_pkey on table articles because other objects depend on it
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DETAIL: view fdv4 depends on constraint articles_pkey on table articles
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HINT: Use DROP ... CASCADE to drop the dependent objects too.
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DROP VIEW fdv4;
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-- prepared query plans: this results in failure on reuse
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PREPARE foo AS
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SELECT id, keywords, title, body, created
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FROM articles
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GROUP BY id;
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EXECUTE foo;
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id | keywords | title | body | created
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----+----------+-------+------+---------
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(0 rows)
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ALTER TABLE articles DROP CONSTRAINT articles_pkey RESTRICT;
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EXECUTE foo; -- fail
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ERROR: column "articles.keywords" must appear in the GROUP BY clause or be used in an aggregate function
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