If you are deleting rows from a table that is referenced by the foreign key of another table, then you will get integrity constraints errors(ORA-02292). This can be avoided by using DELETE CASCADE in Oracle
Let’s take an example. In this, we will first create the sample tables, then insert rows and then try for the delete statement
CREATE TABLE "EMP" ( "EMPNO" NUMBER(4,0), "ENAME" VARCHAR2(10), "JOB" VARCHAR2(9), "MGR" NUMBER(4,0), "HIREDATE" DATE, "SAL" NUMBER(7,2), "COMM" NUMBER(7,2), "DEPTNO" NUMBER(2,0), CONSTRAINT "PK_EMP" PRIMARY KEY ("EMPNO"), CONSTRAINT "FK_DEPTNO" FOREIGN KEY ("DEPTNO") REFERENCES "DEPT" ("DEPTNO") ENABLE ); CREATE TABLE "DEPT" ( "DEPTNO" NUMBER(2,0), "DNAME" VARCHAR2(14), "LOC" VARCHAR2(13), CONSTRAINT "PK_DEPT" PRIMARY KEY ("DEPTNO") )
Now once the table is created, we insert a couple of sample rows to demonstrate the situation
SQL>
insert into DEPT values(10, 'ACCOUNTING', 'NEW YORK');
insert into dept values(20, 'RESEARCH', 'DALLAS');
insert into dept values(30, 'RESEARCH', 'DELHI');
insert into dept values(40, 'RESEARCH', 'MUMBAI');
insert into emp values( 7698, 'BLAKE', 'MANAGER', 7839, to_date('1-5-2007','dd-mm-yyyy'), 2850, null, 10 );
insert into emp values( 7782, 'CLARK', 'MANAGER', 7839, to_date('9-6-2008','dd-mm-yyyy'), 2450, null, 10 );
insert into emp values( 7788, 'SCOTT', 'ANALYST', 7566, to_date('9-6-2012','dd-mm-yyyy'), 3000, null, 20 );
insert into emp values( 7789, 'TPM', 'ANALYST', 7566, to_date('9-6-2017','dd-mm-yyyy'), 3000, null, null );
insert into emp values( 7560, 'T1OM', 'ANALYST', 7567, to_date('9-7-2017','dd-mm-yyyy'), 4000, null, 20 );
insert into emp values( 7790, 'TOM', 'ANALYST', 7567, to_date('9-7-2017','dd-mm-yyyy'), 4000, null, null );
commit;
SQL> select * from emp;
EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO
---------- ---------- --------- ---------- --------- ---------- ---------
7698 BLAKE MANAGER 7839 01-MAY-07 2850 10
7782 CLARK MANAGER 7839 09-JUN-08 2450 10
7788 SCOTT ANALYST 7566 09-JUN-12 3000 20
7789 TPM ANALYST 7566 09-JUN-17 3000
7790 TOM ANALYST 7567 09-JUL-17 4000
4534 xyz 1000 20
4576 abc 1000
7560 T1OM ANALYST 7567 09-JUL-17 4000 20
SQL> delete from dept;
delete from dept
*
ERROR at line 1:
ORA-02292: integrity constraints FK_DEPTNO violated -child record found
ORA-02292 can be avoided if we specify on delete cascade option while creating the EMP table. Then when all the rows of the dept are deleted, all the records from EMP are also deleted. This is true to single row delete also, all the records pertaining to that are deleted from the EMP table also
CREATE TABLE "EMP"
( "EMPNO" NUMBER(4,0),
"ENAME" VARCHAR2(10),
"JOB" VARCHAR2(9),
"MGR" NUMBER(4,0),
"HIREDATE" DATE,
"SAL" NUMBER(7,2),
"COMM" NUMBER(7,2),
"DEPTNO" NUMBER(2,0),
CONSTRAINT "PK_EMP" PRIMARY KEY ("EMPNO"),
CONSTRAINT "FK_DEPTNO" FOREIGN KEY ("DEPTNO")
REFERENCES "DEPT" ("DEPTNO") ENABLE
ON DELETE CASCADE
);
CREATE TABLE "DEPT"
( "DEPTNO" NUMBER(2,0),
"DNAME" VARCHAR2(14),
"LOC" VARCHAR2(13),
CONSTRAINT "PK_DEPT" PRIMARY KEY ("DEPTNO")
)
SQL> desc emp
Name Null? Type
----------------------------------------- -------- ----------------
EMPNO NOT NULL NUMBER(4)
ENAME VARCHAR2(10)
JOB VARCHAR2(9)
MGR NUMBER(4)
HIREDATE DATE
SAL NUMBER(7,2)
COMM NUMBER(7,2)
DEPTNO NUMBER(2)
SQL>
SQL> desc dept
Name Null? Type
----------------------------------------- -------- ---------------
DEPTNO NOT NULL NUMBER(2)
DNAME VARCHAR2(14)
LOC VARCHAR2(13)
SQL>insert into DEPT values(10, 'ACCOUNTING', 'NEW YORK');
insert into dept values(20, 'RESEARCH', 'DALLAS');
insert into dept values(30, 'RESEARCH', 'DELHI');
insert into dept values(40, 'RESEARCH', 'MUMBAI');
insert into emp values( 7698, 'BLAKE', 'MANAGER', 7839, to_date('1-5-2007','dd-mm-yyyy'), 2850, null, 10 );
insert into emp values( 7782, 'CLARK', 'MANAGER', 7839, to_date('9-6-2008','dd-mm-yyyy'), 2450, null, 10 );
insert into emp values( 7788, 'SCOTT', 'ANALYST', 7566, to_date('9-6-2012','dd-mm-yyyy'), 3000, null, 20 );
insert into emp values( 7789, 'TPM', 'ANALYST', 7566, to_date('9-6-2017','dd-mm-yyyy'), 3000, null, null );
insert into emp values( 7560, 'T1OM', 'ANALYST', 7567, to_date('9-7-2017','dd-mm-yyyy'), 4000, null, 20 );
insert into emp values( 7790, 'TOM', 'ANALYST', 7567, to_date('9-7-2017','dd-mm-yyyy'), 4000, null, null );
commit;
SQL> select * from emp;
EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO
---------- ---------- --------- ---------- --------- ---------- -------
7698 BLAKE MANAGER 7839 01-MAY-07 2850 10
7782 CLARK MANAGER 7839 09-JUN-08 2450 10
7788 SCOTT ANALYST 7566 09-JUN-12 3000 20
7789 TPM ANALYST 7566 09-JUN-17 3000
7790 TOM ANALYST 7567 09-JUL-17 4000
4534 xyz 1000 20
4576 abc 1000
7560 T1OM ANALYST 7567 09-JUL-17 4000 20
SQL> delete from dept;
4 rows deleted
SQL> commit;
SQL> Select count(*) from emp
0 rows
So all the records from emp are also deleted and we have not received any errors also which we are getting in the earlier example
Hope you like this post on oracle delete cascade
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