PostgreSQL/Postgre SQL/For

Nested for loop

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=#
postgres=# CREATE TABLE "subjects" (
postgres(#      "id" integer NOT NULL,
postgres(#      "subject" text,
postgres(#      "location" text,
postgres(#      Constraint "subjects_pkey" Primary Key ("id")
postgres(# );
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "subjects_pkey" for table "subjects"
CREATE TABLE
postgres=#
postgres=# insert into subjects values (0,  "Arts", "Creativity St");
INSERT 0 1
postgres=# insert into subjects values (1,  "Business", "Productivity Ave");
INSERT 0 1
postgres=# insert into subjects values (2,  "Children", "Books  Kids Ct");
INSERT 0 1
postgres=# insert into subjects values (3,  "Classics", "Academic Rd");
INSERT 0 1
postgres=# insert into subjects values (4,  "Computers", "Productivity Ave");
INSERT 0 1
postgres=# insert into subjects values (5,  "Cooking", "Creativity St");
INSERT 0 1
postgres=# insert into subjects values (6,  "Drama", "Main St");
INSERT 0 1
postgres=# insert into subjects values (7,  "Entertainment", "Main St");
INSERT 0 1
postgres=# insert into subjects values (8,  "History", "Academic Rd");
INSERT 0 1
postgres=# insert into subjects values (9,  "Horror", "Black Raven Dr");
INSERT 0 1
postgres=# insert into subjects values (10, "Mystery", "Black Raven Dr");
INSERT 0 1
postgres=# insert into subjects values (11, "Poetry", "Sunset Dr");
INSERT 0 1
postgres=# insert into subjects values (12, "Religion", "Regina");
INSERT 0 1
postgres=# insert into subjects values (13, "Romance", "Main St");
INSERT 0 1
postgres=# insert into subjects values (14, "Science", "Productivity Ave");
INSERT 0 1
postgres=# insert into subjects values (15, "Science Fiction", "Main St");
INSERT 0 1
postgres=#
postgres=# select * from subjects;
 id |     subject     |     location
----+-----------------+------------------
  0 | Arts            | Creativity St
  1 | Business        | Productivity Ave
  2 | Children        | Books   Kids Ct
  3 | Classics        | Academic Rd
  4 | Computers       | Productivity Ave
  5 | Cooking         | Creativity St
  6 | Drama           | Main St
  7 | Entertainment   | Main St
  8 | History         | Academic Rd
  9 | Horror          | Black Raven Dr
 10 | Mystery         | Black Raven Dr
 11 | Poetry          | Sunset Dr
 12 | Religion        | Regina
 13 | Romance         | Main St
 14 | Science         | Productivity Ave
 15 | Science Fiction | Main St
(16 rows)
postgres=#
postgres=#
postgres=#
postgres=# drop function extract_all_titles2();
DROP FUNCTION
postgres=#
postgres=# CREATE FUNCTION "extract_all_titles2" () RETURNS text AS "
postgres"#   DECLARE
postgres"#     sub_id INTEGER;
postgres"#     text_output TEXT = "" "";
postgres"#     sub_title TEXT;
postgres"#     row_data books%ROWTYPE;
postgres"#   BEGIN
postgres"#     FOR i IN 0..15 LOOP
postgres"#       SELECT INTO sub_title subject FROM subjects WHERE id = i;
postgres"#       text_output = text_output || """" || sub_title || "":"";
postgres"#
postgres"#       FOR row_data IN SELECT * FROM books
postgres"#         WHERE subject_id = i  LOOP
postgres"#
postgres"#         text_output := text_output || row_data.title || """";
postgres"#
postgres"#       END LOOP;
postgres"#     END LOOP;
postgres"#     RETURN text_output;
postgres"#   END;
postgres"# " LANGUAGE "plpgsql";
CREATE FUNCTION
postgres=#
postgres=# select extract_all_titles2();
                                                                                                                                extract_all_titles2
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
  Arts:CBusiness:Children:OracleSql ServerPostgre SQLPythonClassics:2DComputers:Programming PythonLearning PythonPerl CookbookPractical PostgreSQLCooking:Drama:Java by APIEntertainment:History:Horror:JavaC++Mystery:Poetry:Religion:Romance:Science:Science Fiction:JavascriptC#
(1 row)
postgres=#
postgres=#
postgres=# drop table books;
DROP TABLE
postgres=# drop table subjects;
DROP TABLE
postgres=#