“How to fix trigger in oracle pl/sql? - oracle

Question

Problem:
Need a TRIGGER for the Table A which does the following:
Each time an INSERT is made into Table A on column TRT_PROCEDURE value, add 1
to the column 'TRT_INS_COUNT' in the table B. If the TRT_PROCEDURE value does
not exist in the table B, add a row to the table B for the procedure setting
TRT_INS_COUNT to 1.
Each time a DELETE is made on Table A, add 1 to the column TRT_DEL_COUNT in
table B for that Procedure value if it exists in the table B. If it does not
exist in the table B, add a row to the table B for the procedure and set
TRT_DEL_COUNT to 1.
Each time an UPDATE occurs for Column TRT_PROCEDURE in TABLE A, add 1 to the
column TRT_UPD_COUNT in table B. If it is not in the table B, add a row to
the table B for the procedure value and set TRT_UPD_COUNT to 1. If the Column
TRT_PROCEDURE value in TABLE A is changed, add 1 to the TRT_UPD_COUNT for the
old procedure value.
Test by doing several INSERTs, DELETEs, and UPDATEs and then display the table B.
Updates: whenever an value of trt_procedure is inserted into table B, the second same trt_procedure (e.g '88-20') cannot be correctly counted into its designated count field. Not sure where went wrong.
TABLE A
Name Null Type
TRT_ID NOT NULL NUMBER(3)
PAT_NBR NUMBER(4)
PHYS_ID NUMBER(3)
TRT_PROCEDURE VARCHAR2(5)
TRT_DATE DATE
TABLE B
Name Null Type
TRT_PROCEDURE NOT NULL VARCHAR2(5)
TRT_INS_COUNT NUMBER(3)
TRT_DEL_COUNT NUMBER(3)
TRT_UPD_COUNT NUMBER(3)
TEST SAMPLES
INSERT INTO A VALUES (11, 8031,101,'88-20',sysdate );
INSERT INTO A VALUES (12, 5872,101,'60-00',sysdate );
UPDATE A SET trt_procedure = '88-20' WHERE trt_id=6;
/*row trt_id =6 cloumn trt_procedure old value '54-60'
new value '88-20', which means Table B row '88-20' and
row '54-60 both trt_upd_count should add 1*/
DELETE FROM A WHERE trt_id=1;
/*row trt_id =1 cloumn trt_procedure value also '88-20', which means
that Table B row '88-20' trt_del_count should also add 1*/
CREATE OR REPLACE TRIGGER trt_stats_trg
BEFORE INSERT OR UPDATE OR DELETE OF TRT_procedure ON A FOR EACH ROW
BEGIN
IF INSERTING THEN
UPDATE B SET trt_ins_count = trt_ins_count+1
WHERE B.trt_procedure = :new.trt_procedure;
IF SQL%NOTFOUND THEN
INSERT INTO B (trt_procedure, trt_ins_count)
VALUES (:new.trt_procedure, 1);
END IF;
ELSIF UPDATING THEN
UPDATE B SET trt_upd_count = trt_upd_count+1
WHERE B.trt_procedure = :old.trt_procedure;
IF SQL%NOTFOUND THEN
INSERT INTO B (trt_procedure, trt_upd_count)
VALUES (:old.trt_procedure, 1);
END IF;
UPDATE B SET trt_upd_count = trt_upd_count+1
WHERE B.trt_procedure = :new.trt_procedure;
IF SQL%NOTFOUND THEN
INSERT INTO B (trt_procedure, trt_upd_count)
VALUES (:new.trt_procedure, 1);
END IF;
ELSIF DELETING THEN
UPDATE B SET trt_del_count = trt_del_count+1
WHERE B.trt_procedure = :old.trt_procedure;
IF SQL%NOTFOUND THEN
INSERT INTO B (trt_procedure, trt_del_count)
VALUES (:old.trt_procedure, 1);
END IF;
END IF;
END trt_stats_trg;

Answer 1

Here you go, with a few fixes.
The tables:
create table a(
TRT_ID NUMBER(3) NOT NULL ,
PAT_NBR NUMBER(4),
PHYS_ID NUMBER(3),
TRT_PROCEDURE VARCHAR2(5),
TRT_DATE DATE
);
create table b(
TRT_PROCEDURE VARCHAR2(5) NOT NULL,
TRT_INS_COUNT NUMBER(3),
TRT_DEL_COUNT NUMBER(3),
TRT_UPD_COUNT NUMBER(3)
);
And the trigger
CREATE OR REPLACE TRIGGER trt_stats_trg
BEFORE INSERT OR UPDATE OR DELETE ON A FOR EACH ROW
BEGIN
IF INSERTING THEN
UPDATE B SET trt_ins_count = nvl(trt_ins_count,0)+1
WHERE B.trt_procedure = :new.trt_procedure;
IF SQL%NOTFOUND THEN
INSERT INTO B (trt_procedure, trt_ins_count)
VALUES (:new.trt_procedure, 1);
END IF;
ELSIF UPDATING('TRT_PROCEDURE') THEN
if nvl(:old.trt_procedure, 'X') <> nvl(:new.trt_procedure, 'X') then
UPDATE B SET trt_upd_count = nvl(trt_upd_count,0)+1
WHERE B.trt_procedure = :old.trt_procedure;
IF SQL%NOTFOUND THEN
INSERT INTO B (trt_procedure, trt_upd_count)
VALUES (:old.trt_procedure, 1);
END IF;
UPDATE B SET trt_upd_count = nvl(trt_upd_count,0)+1
WHERE B.trt_procedure = :new.trt_procedure;
IF SQL%NOTFOUND THEN
INSERT INTO B (trt_procedure, trt_upd_count)
VALUES (:new.trt_procedure, 1);
END IF;
end if;
ELSIF DELETING THEN
UPDATE B SET trt_del_count = nvl(trt_del_count, 0)+1
WHERE B.trt_procedure = :old.trt_procedure;
IF SQL%NOTFOUND THEN
INSERT INTO B (trt_procedure, trt_del_count)
VALUES (:old.trt_procedure, 1);
END IF;
END IF;
END trt_stats_trg;
/
Key points:
You can use UPDATING('COLUMN_NAME') to detect when the SQL affects a specific column.
When UPDATING, you may wish to check for non-changing updates, where a column with value "ABC" is being updated to "ABC". This often happens in frameworks that simply include all columns in an update even when they are not really changing. Detect this with something similar to if nvl(:old.trt_procedure, 'X') <> nvl(:new.trt_procedure, 'X') then.
Table B does not have default values for the counts, so when the original trigger tried to update table B, it succeeded...in updating NULL to NULL, as that's what happens when you add 1 to NULL. This can be addressed by either assigning a default value of 0 to the columns in the table or by using NVL(trt_upd_count,0) + 1 instead of trt_upd_count + 1.
Finally, watch out for usages of :new and :old. It looks like they are correct in this trigger, but it will depend on your business case.

Answer 2

In the IF INSERTING section of your trigger you have
UPDATE B
SET trt_ins_count = trt_ins_count+1
WHERE :old.trt_procedure = :new.trt_procedure;
When inserting a new row all values in the :OLD pseudorow are NULL and thus your UPDATE will never update anything. I think you meant
UPDATE B
SET trt_ins_count = trt_ins_count+1
WHERE B.trt_procedure = :new.trt_procedure;
Give that a try and see if that helps solve your problem.