SQL Using Procedures Along With Triggers - sql

Question

I am trying to create some triggers and procedures to auto populate some tables in my database. I have two tables, Users and Utilities.
Users Table:
CREATE TABLE USERS (
User_id Number(38,0) NOT NULL PRIMARY KEY,
User_name char(18) NULL ,
Storage_Size varchar(18) NULL ,
Memory_Usage Number(38,0) NULL
);
Utilities Table
CREATE TABLE UTILITIES (
Utility_id Number(38,0) NOT NULL PRIMARY KEY,
Utility_Name varchar(18) NULL ,
Utility_Cost Number(38,0) NULL ,
Running char(4) NULL ,
User_id Number(38,0) NULL ,
);
Now what I would like to take place in my DB.
When a User is INSERTED into USERS table it fires off a trigger.
This trigger will then insert a bunch of Utilities into the UTILITIES table (User_ID will match the User_ID that was just created) for the User that was created.
After Utilities have been inserted into UTILITIES table I would then like to run a procedure that will SUM(Utility_Cost) in the UTILITIES table and store the SUM in USERS.Memory_Usage WHERE the USER_ID matches.
What I have created so far:
Trigger to fire after INSERT on USERS table:
CREATE OR REPLACE TRIGGER users_after_insert
AFTER INSERT ON USERS
BEGIN
INSERT INTO UTILITIES (UTILITY_NAME, RUNNING, USER_ID, UTILITY_ID, UTILITY_COST)
VALUES
('Javaw.exe', 'YES', :new.USER_ID, seq_utility_id.nextval
, round(dbms_random.value(25000, 100000)));
sum_data();
END;
Procedure to be called from trigger:
CREATE OR REPLACE PROCEDURE sum_data
IS
BEGIN
UPDATE USERS
SET MEMORY_USAGE = (SELECT SUM(UTILITY_COST)
FROM UTILITIES
WHERE USERS.USER_ID = UTILITIES.USER_ID)
WHERE USERS.User_id = :new.User_id;
END;
However when I try and INSERT into the USERS table I get:
ORA-04091: table STUDENT052.USERS is mutating, trigger/function may not see it
ORA-06512: at "STUDENT052.SUM_DATA", line 4
ORA-06512: at "STUDENT052.USERS_AFTER_INSERT", line 5
ORA-04088: error during execution of trigger 'STUDENT052.USERS_AFTER_INSERT'
Does anyone have any idea why this is happening? Any information would be greatly appreciated. Thanks!

Answer 1

You will have to call the procedure separately and update the table, since the data is still not committed and the procedure will try update the same table, it wont work. Apart from that I have executed the trigger and it will populate your utilities table.
SQL> CREATE TABLE USERS (
2 User_id Number(38,0) NOT NULL PRIMARY KEY,
3 User_name char(18) NULL ,
4 Storage_Size varchar(18) NULL ,
5 Memory_Usage Number(38,0) NULL
6 );
Table created.
SQL> CREATE TABLE UTILITIES (
2 Utility_id Number(38,0) NOT NULL PRIMARY KEY,
3 Utility_Name varchar(18) NULL ,
4 Utility_Cost Number(38,0) NULL ,
5 Running char(4) NULL ,
6 User_id Number(38,0) NULL
7 );
Table created.
SQL> CREATE SEQUENCE seq_utility
2 MINVALUE 1
3 MAXVALUE 100
4 START WITH 1
5 INCREMENT BY 1
6 CACHE 5;
Sequence created.
SQL> CREATE OR REPLACE PROCEDURE sum_data ( user_id number) is
2 luser_id number:=user_id;
3 BEGIN
4 UPDATE USERS
5 SET MEMORY_USAGE = (SELECT SUM(UTILITY_COST) FROM UTILITIES WHERE USERS.USER_ID =luser_id);
6 END;
7 /
Procedure created.
SQL> CREATE OR REPLACE TRIGGER users_after_insert
2 AFTER INSERT ON USERS
3 FOR EACH ROW
4 BEGIN
5 INSERT INTO UTILITIES (UTILITY_NAME, RUNNING, USER_ID, UTILITY_ID, UTILITY_COST)
6 VALUES
7 ('Javaw.exe', 'YES', :New.USER_ID, seq_utility_id.nextval, round(dbms_random.value(25000, 100000)));
8 --sum_data(:New.USER_ID);
9 END;
10
11 /
Trigger created.
SQL> insert into users (user_id,user_name) values (125,'TESTUSER');
1 row created.
SQL> select * from utilities;
UTILITY_ID UTILITY_NAME UTILITY_COST RUNN USER_ID
---------- ------------------ ------------ ---- ----------
4 Javaw.exe 68271 YES
5 Javaw.exe 62481 YES 124
10 Javaw.exe 60727 YES 125
SQL> select * from users;
USER_ID USER_NAME STORAGE_SIZE MEMORY_USAGE
---------- ------------------ ------------------ ------------
123 TESTUSER
124 TESTUSER
125 TESTUSER
EDIT
SQL> CREATE OR REPLACE TRIGGER users_after_insert
2 AFTER INSERT ON USERS
3 FOR EACH ROW
4 BEGIN
5 INSERT INTO UTILITIES (UTILITY_NAME, RUNNING, USER_ID, UTILITY_ID, UTILITY_COST)
6 VALUES
7 ('Javaw.exe', 'YES', :New.USER_ID, seq_utility_id.nextval, round(dbms_random.value(25000, 100000)));
8 commit;
9 sum_data(:New.USER_ID);
10 END;
11
12 /
Trigger created.
SQL> insert into users (user_id,user_name) values (126,'TESTUSER');
insert into users (user_id,user_name) values (126,'TESTUSER')
*
ERROR at line 1:
ORA-04092: cannot COMMIT in a trigger
ORA-06512: at "SCOTT.USERS_AFTER_INSERT", line 5
ORA-04088: error during execution of trigger 'SCOTT.USERS_AFTER_INSERT'
A commit within autonomous pragma transaction:
SQL> CREATE OR REPLACE TRIGGER users_after_insert
2 AFTER INSERT ON USERS
3 FOR EACH ROW
4 declare
5 PRAGMA AUTONOMOUS_TRANSACTION;
6 BEGIN
7 commit;
8 INSERT INTO UTILITIES (UTILITY_NAME, RUNNING, USER_ID, UTILITY_ID, UTILITY_COST)
9 VALUES
10 ('Javaw.exe', 'YES', :New.USER_ID, seq_utility_id.nextval, round(dbms_random.value(25000, 100000)));
11 sum_data(:New.USER_ID);
12 END;
13
14 /
Trigger created.
SQL> insert into users (user_id,user_name) values (126,'TESTUSER');
insert into users (user_id,user_name) values (126,'TESTUSER')
*
ERROR at line 1:
ORA-06519: active autonomous transaction detected and rolled back
ORA-06512: at "SCOTT.USERS_AFTER_INSERT", line 9
ORA-04088: error during execution of trigger 'SCOTT.USERS_AFTER_INSERT'
EDIT2
SQL> create view users_views as select a.user_id,a.user_name,SUM(p.UTILITY_COST) as "memory_usage"
2 from users a,utilities p where a.user_id=p.user_id group by a.user_id,a.user_name;
View created.
SQL> select * from users_views;
USER_ID USER_NAME memory_usage
---------- ------------------ ------------
125 TESTUSER 60727
124 TESTUSER 62481
SQL>

Answer 2

Yes, read up on mutating triggers. You're trying to update a record being inserted at the same time, and if you're trying to insert multiple utilities, well, it becomes a real mess.
Why not instead create a view on the tables that includes a column computing the memory usage? Or try a virtual column (or function-based column) on the users table that's based on the other table. (I haven't tested that across tables, so I can't say whether it would work or not.)