create index, Oracle - sql

Question

I have Oracle database. I want to create INDEX:
CREATE INDEX indexID ON Employee(id_employee);
But it writes -> SQL Error: ORA-01408: such column list already indexed
So before create index I put:
DROP INDEX indexID;
But it writes -> SQL Error: ORA-01418: specified index does not exist
my Employee table:
CREATE TABLE Employee (
id_employee NUMBER(5) NOT NULL,
name VARCHAR(25) NOT NULL,
surname VARCHAR(25) NOT NULL,
day_of_birth DATE NOT NULL,
salary NUMBER(6) NOT NULL,
PRIMARY KEY(id_employee)
);
Have you some idea? it looks like index does not create.

Answer 1

You have a different index on that column.
Say you create the table like this:
SQL> CREATE TABLE Employee (
2 id_employee NUMBER(5) NOT NULL ,
3 name VARCHAR(25) NOT NULL,
4 surname VARCHAR(25) NOT NULL,
5 day_of_birth DATE NOT NULL,
6 salary NUMBER(6) NOT NULL
7 );
Table created.
Then you add the PK constraint:
SQL> alter table employee add primary key(id_employee);
Table altered.
Now Oracle already created a unique index on the PK field, so you already have it, with no need for manual creation.
SQL> select index_name, column_name
2 from user_ind_columns c
3 inner join user_indexes i
4 using (index_name)
5 where i.table_name = 'EMPLOYEE';
INDEX_NAME COLUMN_NAME
-------------------- --------------------
SYS_C007892 ID_EMPLOYEE
In your example:
SQL> CREATE TABLE Zamestnanec (
2 id_zamestnance NUMBER(5) PRIMARY KEY ,
3 jmeno VARCHAR(25) NOT NULL,
4 prijmeni VARCHAR(25) NOT NULL,
5 datum_narozeni DATE NOT NULL,
6 prava CHAR(3) CHECK(prava IN ('ano', 'ne')) NOT NULL,
7 plat NUMBER(6) NOT NULL
8 );
Table created.
SQL> select index_name, column_name
2 from user_ind_columns c
3 inner join user_indexes i
4 using (index_name)
5 where i.table_name = 'ZAMESTNANEC';
INDEX_NAME COLUMN_NAME
-------------------- --------------------
SYS_C007899 ID_ZAMESTNANCE
I slightly modified your syntax; besides, you can avoid the NOT NULL constraint on a PK field: the PK will force the field to be NOT NULL.
See here for a similar problem.

Answer 2

The CREATE TABLE for ZAMESTNANEC is
CREATE TABLE Zamestnanec (
id_zamestnance NUMBER(5) NOT NULL,
jmeno VARCHAR(25) NOT NULL,
prijmeni VARCHAR(25) NOT NULL,
datum_narozeni DATE NOT NULL,
prava CHAR(3) CHECK(prava IN ('ano', 'ne')) NOT NULL,
plat NUMBER(6) NOT NULL,
PRIMARY KEY(id_zamestnance)
);
You've created a primary key constraint for ID_ZAMESTNANCE, which by default creates an index on ID_ZAMESTNANCE; thus you don't need to create another index on ID_ZAMESTNANCE.

Answer 3

I would suggest a freakish solution, but I guarantee you that it will work.
Drop the primary key constraint from the table.
ALTER TABLE Employee
DROP CONSTRAINT pk_id_employee
Drop the index, then…
Create the primary key constraint