PostgreSQL/Table Joins/CROSS JOIN
A simple CROSS JOIN
<source lang="sql">
postgres=# postgres=# postgres=# CREATE TABLE "books" ( postgres(# "id" integer NOT NULL, postgres(# "title" text NOT NULL, postgres(# "author_id" integer, postgres(# "subject_id" integer, postgres(# Constraint "books_id_pkey" Primary Key ("id") postgres(# ); NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "books_id_pkey" for table "books" CREATE TABLE postgres=# postgres=# postgres=# insert into books values (7808, "Java", 4156, 9); INSERT 0 1 postgres=# insert into books values (4513, "Javascript", 1866, 15); INSERT 0 1 postgres=# insert into books values (4267, "C#", 2001, 15); INSERT 0 1 postgres=# insert into books values (1608, "Oracle", 1809, 2); INSERT 0 1 postgres=# insert into books values (1590, "Sql Server", 1809, 2); INSERT 0 1 postgres=# insert into books values (25908, "Postgre SQL", 15990, 2); INSERT 0 1 postgres=# insert into books values (1501, "Python", 2031, 2); INSERT 0 1 postgres=# insert into books values (190, "Java by API", 16, 6); INSERT 0 1 postgres=# insert into books values (1234, "2D", 25041, 3); INSERT 0 1 postgres=# insert into books values (2038, "C", 1644, 0); INSERT 0 1 postgres=# insert into books values (156, "C++", 115, 9); INSERT 0 1 postgres=# insert into books values (41473, "Programming Python", 7805, 4); INSERT 0 1 postgres=# insert into books values (41477, "Learning Python", 7805, 4); INSERT 0 1 postgres=# insert into books values (41478, "Perl Cookbook", 7806, 4); INSERT 0 1 postgres=# insert into books values (41472, "Practical PostgreSQL", 1212, 4); INSERT 0 1 postgres=# postgres=# select * from books;
id | title | author_id | subject_id
+----------------------+-----------+------------
7808 | Java | 4156 | 9 4513 | Javascript | 1866 | 15 4267 | C# | 2001 | 15 1608 | Oracle | 1809 | 2 1590 | Sql Server | 1809 | 2 25908 | Postgre SQL | 15990 | 2 1501 | Python | 2031 | 2 190 | Java by API | 16 | 6 1234 | 2D | 25041 | 3 2038 | C | 1644 | 0 156 | C++ | 115 | 9 41473 | Programming Python | 7805 | 4 41477 | Learning Python | 7805 | 4 41478 | Perl Cookbook | 7806 | 4 41472 | Practical PostgreSQL | 1212 | 4
(15 rows) postgres=# postgres=# CREATE TABLE "authors" ( postgres(# "id" integer NOT NULL, postgres(# "last_name" text, postgres(# "first_name" text, postgres(# Constraint "authors_pkey" Primary Key ("id") postgres(# ); NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "authors_pkey" for table "authors" CREATE TABLE postgres=# postgres=# postgres=# insert into authors values (1111, "Martin", "Jason"); INSERT 0 1 postgres=# insert into authors values (1212, "Worsley", "Robert"); INSERT 0 1 postgres=# insert into authors values (15990, "Mathews", "John"); INSERT 0 1 postgres=# insert into authors values (25041, "Smith", "Williams"); INSERT 0 1 postgres=# insert into authors values (16, "Alcott", "May"); INSERT 0 1 postgres=# insert into authors values (4156, "King", "Stephen"); INSERT 0 1 postgres=# insert into authors values (1866, "Herbert", "Margaret"); INSERT 0 1 postgres=# insert into authors values (1644, "Hogarth", "Celia"); INSERT 0 1 postgres=# insert into authors values (2031, "Brown", "Wise"); INSERT 0 1 postgres=# insert into authors values (115, "Poe", "Allen"); INSERT 0 1 postgres=# insert into authors values (7805, "Lutz", "Mark"); INSERT 0 1 postgres=# insert into authors values (7806, "Rice", "Tom"); INSERT 0 1 postgres=# insert into authors values (1533, "Black", "Chris"); INSERT 0 1 postgres=# insert into authors values (1717, "Brite", "Linda"); INSERT 0 1 postgres=# insert into authors values (2112, "Larry", "Edward"); INSERT 0 1 postgres=# insert into authors values (2001, "Clarke", "Alison"); INSERT 0 1 postgres=# insert into authors values (1213, "Green", "Mary"); INSERT 0 1 postgres=# postgres=# select * from authors;
id | last_name | first_name
+-----------+------------
1111 | Martin | Jason 1212 | Worsley | Robert 15990 | Mathews | John 25041 | Smith | Williams 16 | Alcott | May 4156 | King | Stephen 1866 | Herbert | Margaret 1644 | Hogarth | Celia 2031 | Brown | Wise 115 | Poe | Allen 7805 | Lutz | Mark 7806 | Rice | Tom 1533 | Black | Chris 1717 | Brite | Linda 2112 | Larry | Edward 2001 | Clarke | Alison 1213 | Green | Mary
(17 rows) postgres=# postgres=# postgres=# -- A simple CROSS JOIN postgres=# postgres=# SELECT b.id, title, a.id, last_name postgres-# FROM books AS b CROSS JOIN authors AS a postgres-# WHERE b.author_id = a.id;
id | title | id | last_name
+----------------------+-------+-----------
7808 | Java | 4156 | King 4513 | Javascript | 1866 | Herbert 4267 | C# | 2001 | Clarke 25908 | Postgre SQL | 15990 | Mathews 1501 | Python | 2031 | Brown 190 | Java by API | 16 | Alcott 1234 | 2D | 25041 | Smith 2038 | C | 1644 | Hogarth 156 | C++ | 115 | Poe 41473 | Programming Python | 7805 | Lutz 41477 | Learning Python | 7805 | Lutz 41478 | Perl Cookbook | 7806 | Rice 41472 | Practical PostgreSQL | 1212 | Worsley
(13 rows) postgres=# postgres=# postgres=# postgres=# drop table authors; DROP TABLE postgres=# drop table books; DROP TABLE postgres=# postgres=#
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CROSS JOIN in action
<source lang="sql">
postgres=# postgres=# CREATE TABLE t1 ( postgres(# num int, postgres(# name varchar(10) postgres(# ); CREATE TABLE postgres=# postgres=# insert into t1 values(1,"a"); INSERT 0 1 postgres=# insert into t1 values(2,"b"); INSERT 0 1 postgres=# insert into t1 values(3,"c"); INSERT 0 1 postgres=# postgres=# CREATE TABLE t2 ( postgres(# num int, postgres(# name varchar(10) postgres(# ); CREATE TABLE postgres=# postgres=# insert into t1 values(1,"xxx"); INSERT 0 1 postgres=# insert into t1 values(3,"yyy"); INSERT 0 1 postgres=# insert into t1 values(5,"zzz"); INSERT 0 1 postgres=# postgres=# SELECT * FROM t1 CROSS JOIN t2;
num | name | num | name
+------+-----+------
(0 rows) postgres=# postgres=# postgres=# drop table t1; DROP TABLE postgres=# drop table t2; DROP TABLE postgres=# postgres=#
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