IN A TABLE HAVE ONE COLUMN PRIMARY KEY..IT WILL NOT ALLOWS
NULL VALUES AND DUPLICATE VALUES..INSTEAD OF PRIMARY KEY
WHY CANT WE USE UNIQUE AND NOT NULL.THESE TWO ALSO DOESNT
ACCEPT NULL VALUES IN NOT NULL AND UNIQUE DOESNT ACCEPT
DUPLICATE VALUES?
SO WHAT IS THE DIFEERENCE BETWEEN(UNIQUE,NOT NULL) AND
PRIMARY KEY??????
- 8 Answers
- 8802 Views
- rsystems, I also Faced
- E-Mail Answers
Answer Posted / upendra
Primary key creates Clustered Indexes. Clustered indexes physically sort the data.
Unique can have only Non-clustered indexes, where data are not physically sorted.
| Is This Answer Correct ? | 14 Yes | 1 No |
Post New Answer View All Answers
Explain normalization and what are the advantages of it?
Can you rollback after commit?
What is normalization in sql?
How to look at the current sql*plus system settings?
How do you update sql?
create or replace procedure search_matter(empno varchar2) as sql_stmt varchar2(200); stmt varchar2(200); v_table_name varchar2(200); val_pres number; inp_value varchar2(200); type obj_typ is table of cols.column_name%type index by binary_integer; type all_col is table of varchar2(100) index by binary_integer; typ_obj_typ obj_typ; typ_all_col all_col; begin select object_name bulk collect into typ_obj_typ from user_tables,user_objects where table_name = object_name AND object_type = 'TABLE'; select empno into inp_value from dual; dbms_output.put_line('inp value : '||inp_value); for i in typ_obj_typ.first..typ_obj_typ.last loop v_table_name := NULL; v_table_name := typ_obj_typ(i); dbms_output.put_line(i||':'||typ_obj_typ(i)); dbms_output.put_line('....................'); sql_stmt := 'select column_name from cols where table_name = :1 and data_type in (''CHAR'', ''VARCHAR2'', ''NCHAR'', ''NVARCHAR2'',''NUMBER'')'; EXECUTE IMMEDIATE sql_stmt bulk collect into typ_all_col using typ_obj_typ(i); for inside in typ_all_col.first..typ_all_col.last loop dbms_output.put_line('sql stmt: '||sql_stmt); dbms_output.put_line('column name: '||typ_all_col(inside)||'table name: '||typ_obj_typ(i)); stmt := 'select count(*) from ||typ_obj_typ(i)||'; EXECUTE_IMMEDIATE stmt into val_pres ; if val_pres = 1 then dbms_output.put_line('value present col name: '||typ_all_col(inside)||'table name :'||typ_obj_typ(i)); end if; end loop; dbms_output.put_line('....................'); end loop; exception when others then dbms_output.put_line('sql code '||sqlcode||'Table name: '||v_table_name); dbms_output.put_line('sql message '||sqlerrm); end; Compile-time I am getting below error, Plz help to resolve. LINE/COL ERROR -------- ----------------------------------------------------------------- 47/23 PLS-00103: Encountered the symbol "STMT" when expecting one of the following: := . ( @ % ;
What are tables in sql?
Why commit is not used in triggers?
What is an index in sql with example?
What is nested table in pl sql?
Can a foreign key be null?
What is a primary key sql?
what is the difference difference between procedure and packages
Which column in the user.triggers data dictionary view shows that the trigger is a pl/sql trigger?
How to revise and re-run the last sql command?
