Primary key and relevant not null check constraints....

Question

Hi ,
There are some constraints of primary key type and not null check constraints on columns which constitute each primary key....
Should I/Do I have to drop them....????
Do they burden the db at the time of data validation....????
Thanks...
Sim

Answer 1

Hi,
>>There are some constraints of primary key type and not null check constraints on columns which constitute each primary key..
In fact, a column that constitutes a primary key, by default cannot accept NULL values. In this case, defines a PK column as NOT NULL would not be necessary.
LEGATTI@ORACLE10> create table x (id number constraint pk_x primary key);
Table created.
LEGATTI@ORACLE10> desc x
Name                  Null?    Type
ID                    NOT NULL NUMBER
LEGATTI@ORACLE10> select constraint_name,constraint_type,table_name,search_condition from user_constraints where table_name='X';
CONSTRAINT_NAME                C TABLE_NAME      SEARCH_CONDITION                
PK_X                           P X
LEGATTI@ORACLE10> create table y (id number not null constraint pk_y primary key);
Table created.
LEGATTI@ORACLE10> desc y
Name                  Null?    Type
ID                   NOT NULL NUMBER
LEGATTI@ORACLE10> select constraint_name,constraint_type,table_name,search_condition from user_constraints where table_name='Y';
CONSTRAINT_NAME                C TABLE_NAME      SEARCH_CONDITION
SYS_C006327381 C Y "ID" IS NOT NULL 
PK_Y                           P Y
LEGATTI@ORACLE10> alter table y drop constraint SYS_C006327381;
Table altered.
LEGATTI@ORACLE10> desc y
Name                                      Null?    Type
ID                                        NOT NULL NUMBER
LEGATTI@ORACLE10> insert into y values (NULL);
insert into y values (NULL)
ERROR at line 1:
ORA-01400: cannot insert NULL into ("LEGATTI"."Y"."ID")
LEGATTI@ORACLE10> insert into y values (1);
1 row created.
LEGATTI@ORACLE10> insert into y values (1);
insert into y values (1)
ERROR at line 1:
ORA-00001: unique constraint (LEGATTI.PK_Y) violated
>>Should I/Do I have to drop them....????
I don't see any problem, otherwise, drop the NOT NULL constraint is the same with alter the column table like below:
LEGATTI@ORACLE10> create table z (id number not null constraint pk_z primary key);
Table created.
LEGATTI@ORACLE10> select constraint_name,constraint_type,table_name,search_condition from user_constraints where table_name='Z';
CONSTRAINT_NAME                C TABLE_NAME                     SEARCH_CONDITION
SYS_C006328420 C Z "ID" IS NOT NULL
PK_Z                           P Z
LEGATTI@ORACLE10> desc z
Name                                      Null?    Type
ID                                        NOT NULL NUMBER
LEGATTI@ORACLE10> alter table z modify id NULL;
Table altered.
LEGATTI@ORACLE10> select constraint_name,constraint_type,table_name,search_condition from user_constraints where table_name='Z';
CONSTRAINT_NAME                C TABLE_NAME                     SEARCH_CONDITION
PK_Z                           P Z
LEGATTI@ORACLE10> desc z
Name                                      Null?    Type
ID                                        NOT NULL NUMBERCheers
Legatti