PostgreSQL/Select Query/LIMIT

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Correct operator usage: LIMIT

   <source lang="sql">

postgres=# 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=# -- Correct operator usage postgres=# postgres=# SELECT id + 1 AS id_plus_one, name FROM employee postgres-# ORDER BY id DESC LIMIT 5; 

id_plus_one |  name
+-------- 
         10 | Mary
          9 | Chris
          8 | Alison
          7 | James
          6 | David

(5 rows) postgres=# postgres=# postgres=# postgres=# drop table employee; DROP TABLE postgres=# 

      </source>


Using LIMIT for Natural Join

   <source lang="sql">

postgres=# postgres=# postgres=# CREATE TABLE "editions" ( postgres(# "isbn" text NOT NULL, postgres(# "book_id" integer, postgres(# "edition" integer, postgres(# "publisher_id" integer, postgres(# "publication" date, postgres(# "type" character(1), postgres(# CONSTRAINT "integrity" CHECK (((book_id NOTNULL) AND (edition NOTNULL))), postgres(# Constraint "pkey" Primary Key ("isbn") postgres(# ); NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "pkey" for table "editions" CREATE TABLE postgres=# postgres=# insert into editions values("039480001X", 1608, 1, 59, "1957-03-01", "h"); INSERT 0 1 postgres=# insert into editions values("0451160916", 7808, 1, 75, "1981-08-01", "p"); INSERT 0 1 postgres=# insert into editions values("0394800753", 1590, 1, 59, "1949-03-01", "p"); INSERT 0 1 postgres=# insert into editions values("0590445065", 25908, 1, 150, "1987-03-01", "p"); INSERT 0 1 postgres=# insert into editions values("0694003611", 1501, 1, 65, "1947-03-04", "p"); INSERT 0 1 postgres=# insert into editions values("0679803335", 1234, 1, 102, "1922-01-01", "p"); INSERT 0 1 postgres=# insert into editions values("0760720002", 190, 1, 91, "1868-01-01", "p"); INSERT 0 1 postgres=# insert into editions values("0394900014", 1608, 1, 59, "1957-01-01", "p"); INSERT 0 1 postgres=# insert into editions values("0385121679", 7808, 2, 75, "1993-10-01", "h"); INSERT 0 1 postgres=# insert into editions values("1885418035", 156, 1, 163, "1995-03-28", "p"); INSERT 0 1 postgres=# insert into editions values("0929605942", 156, 2, 171, "1998-12-01", "p"); INSERT 0 1 postgres=# insert into editions values("0441172717", 4513, 2, 99, "1998-09-01", "p"); INSERT 0 1 postgres=# insert into editions values("044100590X", 4513, 3, 99, "1999-10-01", "h"); INSERT 0 1 postgres=# insert into editions values("0451457994", 4267, 3, 101, "2000-09-12", "p"); INSERT 0 1 postgres=# insert into editions values("0451198492", 4267, 3, 101, "1999-10-01", "h"); INSERT 0 1 postgres=# insert into editions values("0823015505", 2038, 1, 62, "1958-01-01", "p"); INSERT 0 1 postgres=# insert into editions values("0596000855", 41473, 2, 113, "2001-03-01", "p"); INSERT 0 1 postgres=# postgres=# select * from editions; 

   isbn    | book_id | edition | publisher_id | publication | type
+---------+---------+--------------+-------------+------ 
039480001X |    1608 |       1 |           59 | 1957-03-01  | h
0451160916 |    7808 |       1 |           75 | 1981-08-01  | p
0394800753 |    1590 |       1 |           59 | 1949-03-01  | p
0590445065 |   25908 |       1 |          150 | 1987-03-01  | p
0694003611 |    1501 |       1 |           65 | 1947-03-04  | p
0679803335 |    1234 |       1 |          102 | 1922-01-01  | p
0760720002 |     190 |       1 |           91 | 1868-01-01  | p
0394900014 |    1608 |       1 |           59 | 1957-01-01  | p
0385121679 |    7808 |       2 |           75 | 1993-10-01  | h
1885418035 |     156 |       1 |          163 | 1995-03-28  | p
0929605942 |     156 |       2 |          171 | 1998-12-01  | p
0441172717 |    4513 |       2 |           99 | 1998-09-01  | p
044100590X |    4513 |       3 |           99 | 1999-10-01  | h
0451457994 |    4267 |       3 |          101 | 2000-09-12  | p
0451198492 |    4267 |       3 |          101 | 1999-10-01  | h
0823015505 |    2038 |       1 |           62 | 1958-01-01  | p
0596000855 |   41473 |       2 |          113 | 2001-03-01  | p

(17 rows) 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=# --Using LIMIT and OFFSET postgres=# postgres=# SELECT isbn, title, publication postgres-# FROM editions NATURAL JOIN books AS b (book_id) postgres-# ORDER BY publication DESC postgres-# LIMIT 5; 

   isbn    |       title        | publication
+--------------------+------------- 
0596000855 | Programming Python | 2001-03-01
0451457994 | C#                 | 2000-09-12
044100590X | Javascript         | 1999-10-01
0451198492 | C#                 | 1999-10-01
0929605942 | C++                | 1998-12-01

(5 rows) postgres=# postgres=# postgres=# postgres=# drop table books cascade; DROP TABLE postgres=# drop table editions cascade; DROP TABLE postgres=# postgres=# 

      </source>
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