Creating stored procedure to insert new rows into a table - sql

Question

I am trying to create a stored procedure which fulfill the following question,
Write a stored procedure called event_registration which handles the participant's entry for an event. When a participant registers for an event, they may also choose to create or join a group.
Your procedure must take four input parameters:
participant number
exhibition date
event type description
group name.
The procedure must:
check if the input exhibition date and event name are valid
check if the participants wants to create/join a group (ie. they provide a group name) and, if provided, whether the group name exists for the input exhibition:
If the group does not exist then the procedure should add a new group and assign this participant as the group leader, or
If the group exists then the procedure should add the participant into the existing group
So the below are my tables:
CREATE TABLE group
(
group_id NUMBER(3) NOT NULL,
group_name VARCHAR2(30) NOT NULL,
exhibition_date DATE NOT NULL,
group_no_members NUMBER(2) NOT NULL,
event_id NUMBER(6) NOT NULL,
entry_no NUMBER(5) NOT NULL,
char_id NUMBER(3)
);
CREATE TABLE event
(
event_id NUMBER(6) NOT NULL,
exhibition_date DATE NOT NULL,
eventtype_code CHAR(3) NOT NULL,
event_starttime DATE NOT NULL
);
CREATE TABLE eventtype
(
eventtype_code CHAR(3) NOT NULL,
eventtype_desc VARCHAR2(50) NOT NULL
);
CREATE TABLE exhibition
(
exhibition_date DATE NOT NULL,
exhibition_name VARCHAR2(50) NOT NULL,
exhibition_director VARCHAR2(50) NOT NULL,
exhibition_location VARCHAR2(50) NOT NULL
);
CREATE TABLE entry
(
event_id NUMBER(6) NOT NULL,
entry_no NUMBER(5) NOT NULL,
entry_starttime DATE,
entry_finishtime DATE,
part_no NUMBER(5) NOT NULL,
group_id NUMBER(3),
char_id NUMBER(3)
);
And this is my procedure:
CREATE OR REPLACE PROCEDURE event_registration
(new_part_no IN NUMBER,
new_exhibition_date IN DATE,
new_eventtype_desc IN VARCHAR2,
new_group_name IN VARCHAR2,
output OUT VARCHAR2)
AS
exhibition_date_and_event_found NUMBER; group_found NUMBER;
BEGIN
SELECT COUNT(*)
INTO exhibition_date_and_event_found
FROM event
NATURAL JOIN eventtype
WHERE exhibition_date = new_exhibition_date
AND eventtype_desc = new_eventtype_desc;
IF (exhibition_date_and_event_found = 0) THEN
output := 'Invalid exhibition date/This exhibition does not have this event type';
ELSE
IF(new_group_name != NULL) THEN
SELECT COUNT(*) INTO group_found FROM group NATURAL JOIN exhibition WHERE group_name = new_group_name AND exhibition_date = new_exhibition_date;
IF(group_found = 0) THEN
INSERT INTO group VALUES ((SELECT COUNT(*)+1 FROM group), new_group_name, TO_DATE(new_exhibition_date, 'DD/MM/YYYY'), 1, (SELECT event_id FROM event NATURAL JOIN eventtype WHERE eventtype_desc = new_eventtype_desc AND exhibition_date = TO_DATE(new_exhibition_date,'DD/MM/YYYY')), (SELECT MAX(entry_no)+1 FROM entry WHERE event_id = (SELECT event_id FROM event NATURAL JOIN eventtype WHERE eventtype_desc = new_eventtype_desc AND exhibition_date = TO_DATE(new_exhibition_date, 'DD/MM/YYYY'))), NULL);
INSERT INTO entry VALUES ((SELECT event_id FROM event NATURAL JOIN eventtype WHERE eventtype_desc = new_eventtype_desc AND exhibition_date = TO_DATE(new_exhibition_date, 'DD/MM/YYYY')), (SELECT MAX(entry_no)+1 FROM entry WHERE event_id = (SELECT event_id FROM event NATURAL JOIN eventtype WHERE eventtype_desc = new_eventtype_desc AND exhibition_date = TO_DATE(new_exhibition_date, 'DD/MM/YYYY'))), NULL, NULL, new_part_no, (SELECT group_id FROM group WHERE group_name = new_group_name), NULL);
ELSE --group already exist
--update the group member number by 1
UPDATE group
SET group_no_members = group_no_members + 1
WHERE group_name = new_group_name;
INSERT INTO entry VALUES ((SELECT event_id FROM event NATURAL JOIN eventtype WHERE eventtype_desc = new_eventtype_desc AND exhibition_date = TO_DATE(new_exhibition_date, 'DD/MM/YYYY')), (SELECT MAX(entry_no)+1 FROM entry WHERE event_id = (SELECT event_id FROM event NATURAL JOIN eventtype WHERE eventtype_desc = new_eventtype_desc AND exhibition_date = TO_DATE(new_exhibition_date, 'DD/MM/YYYY'))), NULL, NULL, new_part_no, (SELECT group_id FROM group WHERE group_name = new_group_name), NULL);
END IF;
ELSE
INSERT INTO entry VALUES ((SELECT event_id FROM event NATURAL JOIN eventtype WHERE eventtype_desc = new_eventtype_desc AND exhibition_date = TO_DATE(new_exhibition_date, 'DD/MM/YYYY')), (SELECT MAX(entry_no)+1 FROM entry WHERE event_id = (SELECT event_id FROM event NATURAL JOIN eventtype WHERE eventtype_desc = new_eventtype_desc AND exhibition_date = TO_DATE(new_exhibition_date, 'DD/MM/YYYY'))), NULL, NULL, new_part_no, NULL, NULL);
END IF;
END IF;
END;
/
The procedure is not done yet but I think it is good enough to be compiled, but when I run it, it gives out errors like
Procedure EVENT_REGISTRATION compiled
LINE/COL ERROR
--------- -------------------------------------------------------------
12/9 PL/SQL: SQL Statement ignored
12/21 PL/SQL: ORA-00947: not enough values
18/9 PL/SQL: SQL Statement ignored
18/21 PL/SQL: ORA-00947: not enough values
21/9 PL/SQL: SQL Statement ignored
21/21 PL/SQL: ORA-00947: not enough values
Errors: check compiler log
Can anybody help me with this? Thank you in advance!

Answer 1

Use constraints on your tables (primary keys, foreign keys, etc.).
Use sequences for primary key values (NEVER use SELECT COUNT(*) + 1 FROM ... to generate ids as you are likely to get duplicates on a parallel system).
If you use constraints then you don't need to check that the exhibition date and event (exhibition?) name are correct as, if they are not, the constraint will raise an exception when you try to against a non-existent relationship.
NEVER use INSERT INTO table_name VALUES (...), you should always explicitly name the columns you are inserting into using:
INSERT INTO table_name (col1, col2, col3) VALUES (value1, value2, value3);
Do not keep using the same query over-and-over to find the event_id. Find it once and store it in a PL/SQL variable and then use the PL/SQL variable the next time.
GROUP is a reserved word; do not use it as an identifier.
You cannot compare a value to NULL using value != NULL as NULL is never equal or not-equal to anything else; you need to use value IS NOT NULL.
Make sure you do not have cyclic referential constraints in your tables (i.e. GROUP has an entry_no which refers to the entry table and the entry table has a group_id column that refers to the GROUP table. You do not need both and when you put constraints in then you will get a cycle.)
Something like:
CREATE TABLE exhibition
(
exhibition_date DATE
PRIMARY KEY
NOT NULL,
exhibition_name VARCHAR2(50)
NOT NULL,
exhibition_director VARCHAR2(50)
NOT NULL,
exhibition_location VARCHAR2(50)
NOT NULL
);
CREATE TABLE eventtype
(
eventtype_code CHAR(3)
PRIMARY KEY
NOT NULL,
eventtype_desc VARCHAR2(50)
NOT NULL
);
CREATE TABLE event
(
event_id NUMBER(6)
NOT NULL
PRIMARY KEY,
exhibition_date REFERENCES exhibition(exhibition_date)
NOT NULL,
eventtype_code REFERENCES eventtype(eventtype_code)
NOT NULL,
event_starttime DATE
NOT NULL
);
CREATE TABLE "GROUP"
(
group_id NUMBER(3)
NOT NULL
PRIMARY KEY,
group_name VARCHAR2(30)
UNIQUE
NOT NULL,
group_no_members NUMBER(2)
NOT NULL,
event_id REFERENCES event(event_id)
NOT NULL,
char_id NUMBER(3)
);
CREATE TABLE entry
(
event_id REFERENCES event(event_id)
NOT NULL,
entry_no NUMBER(5)
PRIMARY KEY
NOT NULL,
entry_starttime DATE,
entry_finishtime DATE,
part_no NUMBER(5)
NOT NULL,
group_id NUMBER(3)
REFERENCES "GROUP"(group_id),
char_id NUMBER(3)
);
Then:
CREATE SEQUENCE group_seq;
CREATE SEQUENCE entry_seq;
Then:
CREATE OR REPLACE PROCEDURE event_registration
(new_part_no IN NUMBER,
new_exhibition_date IN DATE,
new_eventtype_desc IN VARCHAR2,
new_group_name IN VARCHAR2,
output OUT VARCHAR2)
AS
v_event_id EVENT.EVENT_ID%TYPE;
v_group_id "GROUP".GROUP_ID%TYPE;
BEGIN
SELECT e.event_id
INTO v_event_id
FROM event e
INNER JOIN eventtype et
ON (e.eventtype_code = et.eventtype_code)
WHERE exhibition_date = new_exhibition_date
AND eventtype_desc = new_eventtype_desc;
IF new_group_name IS NOT NULL THEN
MERGE INTO "GROUP" g
USING DUAL
ON (g.group_name = new_group_name)
WHEN MATCHED THEN
UPDATE
SET group_no_members = group_no_members + 1
WHEN NOT MATCHED THEN
INSERT (
group_id,
group_name,
group_no_members,
event_id,
char_id
) VALUES (
GROUP_SEQ.NEXTVAL,
new_group_name,
1,
v_event_id,
NULL
);
SELECT group_id
INTO v_group_id
FROM "GROUP"
WHERE group_name = new_group_name;
END IF;
INSERT INTO entry (
event_id,
entry_no,
entry_starttime,
entry_finishtime,
part_no,
group_id,
char_id
)VALUES (
v_event_id,
entry_seq.NEXTVAL,
NULL,
NULL,
new_part_no,
v_group_id,
NULL
);
EXCEPTION
WHEN NO_DATA_FOUND THEN
output := 'Invalid exhibition date/This exhibition does not have this event type';
END;
/
db<>fiddle here