в 13:45, 26 мая 2010

2010-05-26T13:45:56Z

Admin: 1 версия

2010-05-26T10:14:40Z

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==A simple sub-query: subquery return one value==



<source lang="sql">
postgres=#
postgres=# create table job(
postgres(# ID int,
postgres(# title varchar (10));
CREATE TABLE
postgres=#
postgres=#
postgres=# insert into job(ID, title) values(1,"Developer");
INSERT 0 1
postgres=# insert into job(ID, title) values(2,"Tester");
INSERT 0 1
postgres=# insert into job(ID, title) values(3,"Designer");
INSERT 0 1
postgres=# insert into job(ID, title) values(4,"Programmer");
INSERT 0 1
postgres=#
postgres=# select * from job;
id | title
----+------------
1 | Developer
2 | Tester
3 | Designer
4 | Programmer
(4 rows)
postgres=#
postgres=# CREATE TABLE employee (
postgres(# ID int,
postgres(# name varchar(10),
postgres(# salary real,
postgres(# start_date date,
postgres(# city varchar(10),
postgres(# region char(1)
postgres(# );
CREATE TABLE
postgres=#
postgres=# insert into employee (ID, name, salary, start_date, city, region)
postgres-# values (1, "Jason", 40420, "02/01/94", "New York", "W");
INSERT 0 1
postgres=# insert into employee (ID, name, salary, start_date, city, region)
postgres-# values (2, "Robert",14420, "01/02/95", "Vancouver","N");
INSERT 0 1
postgres=# insert into employee (ID, name, salary, start_date, city, region)
postgres-# values (3, "Celia", 24020, "12/03/96", "Toronto", "W");
INSERT 0 1
postgres=# insert into employee (ID, name, salary, start_date, city, region)
postgres-# values (4, "Linda", 40620, "11/04/97", "New York", "N");
INSERT 0 1
postgres=# insert into employee (ID, name, salary, start_date, city, region)
postgres-# values (5, "David", 80026, "10/05/98", "Vancouver","W");
INSERT 0 1
postgres=# insert into employee (ID, name, salary, start_date, city, region)
postgres-# values (6, "James", 70060, "09/06/99", "Toronto", "N");
INSERT 0 1
postgres=# insert into employee (ID, name, salary, start_date, city, region)
postgres-# values (7, "Alison",90620, "08/07/00", "New York", "W");
INSERT 0 1
postgres=# insert into employee (ID, name, salary, start_date, city, region)
postgres-# values (8, "Chris", 26020, "07/08/01", "Vancouver","N");
INSERT 0 1
postgres=# insert into employee (ID, name, salary, start_date, city, region)
postgres-# values (9, "Mary", 60020, "06/09/02", "Toronto", "W");
INSERT 0 1
postgres=#
postgres=# select * from employee;
id | name | salary | start_date | city | region
----+--------+--------+------------+-----------+--------
1 | Jason | 40420 | 1994-02-01 | New York | W
2 | Robert | 14420 | 1995-01-02 | Vancouver | N
3 | Celia | 24020 | 1996-12-03 | Toronto | W
4 | Linda | 40620 | 1997-11-04 | New York | N
5 | David | 80026 | 1998-10-05 | Vancouver | W
6 | James | 70060 | 1999-09-06 | Toronto | N
7 | Alison | 90620 | 2000-08-07 | New York | W
8 | Chris | 26020 | 2001-07-08 | Vancouver | N
9 | Mary | 60020 | 2002-06-09 | Toronto | W
(9 rows)
postgres=#
postgres=#
postgres=# -- A simple sub-query
postgres=#
postgres=# SELECT name FROM employee WHERE id = (SELECT id FROM job where title = "Developer");
name
-------
Jason
(1 row)
postgres=#
postgres=#
postgres=# drop table employee;
DROP TABLE
postgres=# drop table job;
DROP TABLE
postgres=#
postgres=#

</source>

==Comparing sub-query result sets==



<source lang="sql">

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=# -- Comparing sub-query result sets
postgres=#
postgres=# (SELECT title FROM books ORDER BY title DESC LIMIT 7)
postgres-# EXCEPT
postgres-# (SELECT title FROM books ORDER BY title ASC LIMIT 11)
postgres-# ORDER BY title DESC;
title
----------------------
Sql Server
Python
Programming Python
Practical PostgreSQL
(4 rows)
postgres=#
postgres=#
postgres=# drop table books;
DROP TABLE
postgres=#
postgres=#

</source>

==Selecting from a sub-query==



<source lang="sql">

postgres=#
postgres=# CREATE TABLE employee (
postgres(# ID int,
postgres(# name varchar(10),
postgres(# salary real,
postgres(# start_date date,
postgres(# city varchar(10),
postgres(# region char(1)
postgres(# );
CREATE TABLE
postgres=#
postgres=# insert into employee (ID, name, salary, start_date, city, region)
postgres-# values (1, "Jason", 40420, "02/01/94", "New York", "W");
INSERT 0 1
postgres=# insert into employee (ID, name, salary, start_date, city, region)
postgres-# values (2, "Robert",14420, "01/02/95", "Vancouver","N");
INSERT 0 1
postgres=# insert into employee (ID, name, salary, start_date, city, region)
postgres-# values (3, "Celia", 24020, "12/03/96", "Toronto", "W");
INSERT 0 1
postgres=# insert into employee (ID, name, salary, start_date, city, region)
postgres-# values (4, "Linda", 40620, "11/04/97", "New York", "N");
INSERT 0 1
postgres=# insert into employee (ID, name, salary, start_date, city, region)
postgres-# values (5, "David", 80026, "10/05/98", "Vancouver","W");
INSERT 0 1
postgres=# insert into employee (ID, name, salary, start_date, city, region)
postgres-# values (6, "James", 70060, "09/06/99", "Toronto", "N");
INSERT 0 1
postgres=# insert into employee (ID, name, salary, start_date, city, region)
postgres-# values (7, "Alison",90620, "08/07/00", "New York", "W");
INSERT 0 1
postgres=# insert into employee (ID, name, salary, start_date, city, region)
postgres-# values (8, "Chris", 26020, "07/08/01", "Vancouver","N");
INSERT 0 1
postgres=# insert into employee (ID, name, salary, start_date, city, region)
postgres-# values (9, "Mary", 60020, "06/09/02", "Toronto", "W");
INSERT 0 1
postgres=#
postgres=# select * from employee;
id | name | salary | start_date | city | region
----+--------+--------+------------+-----------+--------
1 | Jason | 40420 | 1994-02-01 | New York | W
2 | Robert | 14420 | 1995-01-02 | Vancouver | N
3 | Celia | 24020 | 1996-12-03 | Toronto | W
4 | Linda | 40620 | 1997-11-04 | New York | N
5 | David | 80026 | 1998-10-05 | Vancouver | W
6 | James | 70060 | 1999-09-06 | Toronto | N
7 | Alison | 90620 | 2000-08-07 | New York | W
8 | Chris | 26020 | 2001-07-08 | Vancouver | N
9 | Mary | 60020 | 2002-06-09 | Toronto | W
(9 rows)
postgres=#
postgres=# -- Selecting from a sub-query
postgres=#
postgres=# SELECT "test" AS test, id
postgres-# FROM (SELECT id FROM employee)
postgres-# AS example_sub_query;
test | id
------+----
test | 1
test | 2
test | 3
test | 4
test | 5
test | 6
test | 7
test | 8
test | 9
(9 rows)
postgres=#
postgres=# drop table employee;
DROP TABLE
postgres=#
postgres=#
postgres=#

</source>

==To use a normal value operator on the results of a sub-query, only one field must be returned==



<source lang="sql">
postgres=#
postgres=#
postgres=# create table job(
postgres(# ID int,
postgres(# title varchar (10));
CREATE TABLE
postgres=#
postgres=#
postgres=# insert into job(ID, title) values(1,"Developer");
INSERT 0 1
postgres=# insert into job(ID, title) values(2,"Tester");
INSERT 0 1
postgres=# insert into job(ID, title) values(3,"Designer");
INSERT 0 1
postgres=# insert into job(ID, title) values(4,"Programmer");
INSERT 0 1
postgres=#
postgres=# select * from job;
id | title
----+------------
1 | Developer
2 | Tester
3 | Designer
4 | Programmer
(4 rows)
postgres=#
postgres=# CREATE TABLE employee (
postgres(# ID int,
postgres(# name varchar(10),
postgres(# salary real,
postgres(# start_date date,
postgres(# city varchar(10),
postgres(# region char(1)
postgres(# );
CREATE TABLE
postgres=#
postgres=# insert into employee (ID, name, salary, start_date, city, region)
postgres-# values (1, "Jason", 40420, "02/01/94", "New York", "W");
INSERT 0 1
postgres=# insert into employee (ID, name, salary, start_date, city, region)
postgres-# values (2, "Robert",14420, "01/02/95", "Vancouver","N");
INSERT 0 1
postgres=# insert into employee (ID, name, salary, start_date, city, region)
postgres-# values (3, "Celia", 24020, "12/03/96", "Toronto", "W");
INSERT 0 1
postgres=# insert into employee (ID, name, salary, start_date, city, region)
postgres-# values (4, "Linda", 40620, "11/04/97", "New York", "N");
INSERT 0 1
postgres=# insert into employee (ID, name, salary, start_date, city, region)
postgres-# values (5, "David", 80026, "10/05/98", "Vancouver","W");
INSERT 0 1
postgres=# insert into employee (ID, name, salary, start_date, city, region)
postgres-# values (6, "James", 70060, "09/06/99", "Toronto", "N");
INSERT 0 1
postgres=# insert into employee (ID, name, salary, start_date, city, region)
postgres-# values (7, "Alison",90620, "08/07/00", "New York", "W");
INSERT 0 1
postgres=# insert into employee (ID, name, salary, start_date, city, region)
postgres-# values (8, "Chris", 26020, "07/08/01", "Vancouver","N");
INSERT 0 1
postgres=# insert into employee (ID, name, salary, start_date, city, region)
postgres-# values (9, "Mary", 60020, "06/09/02", "Toronto", "W");
INSERT 0 1
postgres=#
postgres=# select * from employee;
id | name | salary | start_date | city | region
----+--------+--------+------------+-----------+--------
1 | Jason | 40420 | 1994-02-01 | New York | W
2 | Robert | 14420 | 1995-01-02 | Vancouver | N
3 | Celia | 24020 | 1996-12-03 | Toronto | W
4 | Linda | 40620 | 1997-11-04 | New York | N
5 | David | 80026 | 1998-10-05 | Vancouver | W
6 | James | 70060 | 1999-09-06 | Toronto | N
7 | Alison | 90620 | 2000-08-07 | New York | W
8 | Chris | 26020 | 2001-07-08 | Vancouver | N
9 | Mary | 60020 | 2002-06-09 | Toronto | W
(9 rows)
postgres=#
postgres=#
postgres=#
postgres=# --To use a normal value operator on
postgres=# -- the results of a sub-query, only one field must be returned
postgres=#
postgres=# SELECT name FROM employee WHERE id = (SELECT id FROM job);
ERROR: more than one row returned by a subquery used as an expression
postgres=#
postgres=# drop table employee;
DROP TABLE
postgres=# drop table job;
DROP TABLE
postgres=#
postgres=#

</source>

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PostgreSQL/Subquery/Subquery Basics - История изменений

в 13:45, 26 мая 2010

Admin: 1 версия