PostgreSQL/Table Joins/CROSS JOIN
A simple CROSS JOIN
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=#
CROSS JOIN in action
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=#