Difference between Unique key and Unique index

Hi All,
I've got confused in the difference between unique index & unique key in a table.
While we create a unique index on a table, its created as a unique index.
On the other hand, if we create a unique key/constraint on the table, Oracle also creates an index entry for that. So I can find the same name object in all_constraints as well as in all_indexes.
My question here is that if during creation of unique key/constraint, an index is automatically created than why is the need to create unique key and then two objects , while we can create only one object i.e. unique index.
Thanks
Deepak

This is only my understanding and is not according to any documentation, that is as follows.
The unique key (constraint) needs an unique index for achieving constraint of itself.
Developers and users can make any constraint (unique-key, primary-key, foreign-key, not-null ...) to enable,disable and be deferable. Unique key is able to be enabled, disabled, deferable.
On the other hand, the index is used for performance-up originally, unique index itself doesn't have the concept like constraints. The index (including non-unique, unique) can be rebuilded,enabled,disabled etc. But I think that index cannot be set "deferable-builded" automatic.

Similar Messages

Difference between primary key and primary index

Dear All,
Hi... .Could you pls tell me the difference between primary key and primary index.
Thanks...

Hi,
Primary Key : It is one which makes an entry of the field unique.No two distinct rows in a table can have the same value (or combination of values) in those columns.
Eg: first entry is 111, if you again enter value 111 , it doesnot allow 111 again. similarly for the strings or characters or numc etc. Remember that for char or numc or string 'NAME' is not equal to 'name'.
Primary Index: this is related to the performance .A database index is a data structure that improves the speed of operations in a table. Indices can be created using one or more columns, providing the basis for both rapid random lookups and efficient ordering of access to records. The disk space required to store the index is typically less than the storage of the table (since indices usually contain only the key-fields according to which the table is to be arranged, and excludes all the other details in the table), yielding the possibility to store indices into memory from tables that would not fit into it. In a relational database an index is a copy of part of a table. Some databases extend the power of indexing by allowing indices to be created on functions or expressions. For example, an index could be created on upper(last_name), which would only store the uppercase versions of the last_name field in the index.
In a database , we may have a large number of records. At the time of retrieving data from the database based on a condition , it is a burden to the db server. so whenever we create a primary key , a primary index is automatically created by the system.
If you want to maintain indices on other fields which are frequently used in where condition then you can create secondary indices.
Reward points if helpful.
Thanks,
Sirisha..

Difference between PRIMARY KEY and UNIQUE KEY with NOT NULL

What is the difference between PRIMARY KEY and UNIQUE KEY with NOT NULL constraint?
Message was edited by:
Nilesh Hole

Answer for the master!!!
http://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:8743855576462
Thanks,
Karthick

Difference Between Unique Index vs Unique Constraint

Can you tell me
what is the Difference Between Unique Index vs Unique Constraint.
and
Difference Between Unique Index and bitmap index.
Edited by: Nilesh Hole,Pune, India on Aug 22, 2009 10:33 AM

Nilesh Hole,Pune, India wrote:
Can you tell me
what is the Difference Between Unique Index vs Unique Constraint.http://www.jlcomp.demon.co.uk/faq/uk_idx_con.html
and
Difference Between Unique Index and bitmap index.The documentation is your friend:
http://download.oracle.com/docs/cd/B28359_01/server.111/b28318/schema.htm#CNCPT1157
http://download.oracle.com/docs/cd/B19306_01/server.102/b14220/schema.htm#sthref1008
Regards,
Rob.

Difference between primary eindex and secondary index?

hi experts
pls answer me
difference between primary eindex and secondary index?
rewads apply.
thanks.
naresh.

hi,
check this link.
http://help.sap.com/saphelp_47x200/helpdata/en/cf/21eb2d446011d189700000e8322d00/frameset.htm
A difference is made between Primary & Secondary indexes to a table. the primary index consists of the key fields of the table and a pointer to the non-keys-fields of the table. The Primary index is generated automatically when a table is created and is created in the datebase as the same times as the table. It is also possible to define further indexes to a table in the ABAP/4 dictionary, which are then referred to as Secondary indexes.
Always it is not mandatory that an index should have all the key fields of a table. To see the index of a table
goto SE11->specify table name->click on the indexes... button on the application toolbar.
Based on your requirement you can you any of those index fields in the where clause of your query. Always its a better practice to use the index fields in the order specified. While selecting the records from a table it is always better to select the fields in the same order as specified in the table.

Difference between sy-tabix and sy-index?

tell me about sy-tabix and sy-index?what is the difference between sy-tabix and sy-index?
Moderator Message: Please search before posting. Read the [Forum Rules Of Engagement |https://wiki.sdn.sap.com/wiki/display/HOME/RulesofEngagement] for further details.
Edited by: Suhas Saha on Jun 18, 2011 5:33 PM

HI,
Here is a brief description of difference between SY_TABIX and SY_INDEX and using them with several conditions.
SY-TABIX
Current line of an internal table. SY-TABIX is set by the statements below, but only for index tables. The field is either not set or is set to 0 for hashed tables.
APPEND sets SY-TABIX to the index of the last line of the table, that is, it contains the overall number of entries in the table.
COLLECT sets SY-TABIX to the index of the existing or inserted line in the table. If the table has the type HASHED TABLE, SY-TABIX is set to 0.
LOOP AT sets SY-TABIX to the index of the current line at the beginning of each loop lass. At the end of the loop, SY-TABIX is reset to the value that it had before entering the loop. It is set to 0 if the table has the type HASHED TABLE.
READ TABLE sets SY-TABIX to the index of the table line read. If you use a binary search, and the system does not find a line, SY-TABIX contains the total number of lines, or one more than the total number of lines. SY-INDEX is undefined if a linear search fails to return an entry.
SEARCH <itab> FOR sets SY-TABIX to the index of the table line in which the search string is found.
SY-INDEX
In a DO or WHILE loop, SY-INDEX contains the number of loop passes including the current pass.
Hope this helps.
Thank you,
Pavan.

Access path difference between Primary Key and Unique Index

Hi All,
Is there any specific way the oracle optimizer treats Primary key and Unique index differently?
Oracle Version
SQL> select * from v$version;
BANNER
Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production
PL/SQL Release 11.2.0.3.0 - Production
CORE    11.2.0.3.0      Production
TNS for IBM/AIX RISC System/6000: Version 11.2.0.3.0 - Production
NLSRTL Version 11.2.0.3.0 - Production
SQL> Sample test data for Normal Index
SQL> create table t_test_tab(col1 number, col2 number, col3 varchar2(12));
Table created.
SQL> create sequence seq_t_test_tab start with 1 increment by 1 ;
Sequence created.
SQL> insert into t_test_tab select seq_t_test_tab.nextval, round(dbms_random.value(1,999)) , 'B'||round(dbms_random.value(1,50))||'A' from dual connect by level < 100000;
99999 rows created.
SQL> commit;
Commit complete.
SQL> exec dbms_stats.gather_table_stats(USER_OWNER','T_TEST_TAB',cascade => true);
PL/SQL procedure successfully completed.
SQL> select col1 from t_test_tab;
99999 rows selected.
Execution Plan
Plan hash value: 1565504962
| Id | Operation         | Name       | Rows | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT |            | 99999 |   488K|    74   (3)| 00:00:01 |
|   1 | TABLE ACCESS FULL| T_TEST_TAB | 99999 |   488K|    74   (3)| 00:00:01 |
Statistics
          1 recursive calls
          0 db block gets
       6915 consistent gets
        259 physical reads
          0 redo size
    1829388 bytes sent via SQL*Net to client
      73850 bytes received via SQL*Net from client
       6668 SQL*Net roundtrips to/from client
          0 sorts (memory)
          0 sorts (disk)
      99999 rows processed
SQL> create index idx_t_test_tab on t_test_tab(col1);
Index created.
SQL> exec dbms_stats.gather_table_stats('USER_OWNER','T_TEST_TAB',cascade => true);
PL/SQL procedure successfully completed.
SQL> select col1 from t_test_tab;
99999 rows selected.
Execution Plan
Plan hash value: 1565504962
| Id | Operation         | Name       | Rows | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT |            | 99999 |   488K|    74   (3)| 00:00:01 |
|   1 | TABLE ACCESS FULL| T_TEST_TAB | 99999 |   488K|    74   (3)| 00:00:01 |
Statistics
          1 recursive calls
          0 db block gets
       6915 consistent gets
          0 physical reads
          0 redo size
    1829388 bytes sent via SQL*Net to client
      73850 bytes received via SQL*Net from client
       6668 SQL*Net roundtrips to/from client
          0 sorts (memory)
          0 sorts (disk)
      99999 rows processed
SQL> Sample test data when using Primary Key
SQL> create table t_test_tab1(col1 number, col2 number, col3 varchar2(12));
Table created.
SQL> create sequence seq_t_test_tab1 start with 1 increment by 1 ;
Sequence created.
SQL> insert into t_test_tab1 select seq_t_test_tab1.nextval, round(dbms_random.value(1,999)) , 'B'||round(dbms_random.value(1,50))||'A' from dual connect by level < 100000;
99999 rows created.
SQL> commit;
Commit complete.
SQL> exec dbms_stats.gather_table_stats('USER_OWNER','T_TEST_TAB1',cascade => true);
PL/SQL procedure successfully completed.
SQL> select col1 from t_test_tab1;
99999 rows selected.
Execution Plan
Plan hash value: 1727568366
| Id | Operation         | Name        | Rows | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT |             | 99999 |   488K|    74   (3)| 00:00:01 |
|   1 | TABLE ACCESS FULL| T_TEST_TAB1 | 99999 |   488K|    74   (3)| 00:00:01 |
Statistics
          1 recursive calls
          0 db block gets
       6915 consistent gets
          0 physical reads
          0 redo size
    1829388 bytes sent via SQL*Net to client
      73850 bytes received via SQL*Net from client
       6668 SQL*Net roundtrips to/from client
          0 sorts (memory)
          0 sorts (disk)
      99999 rows processed
SQL> alter table t_test_tab1 add constraint pk_t_test_tab1 primary key (col1);
Table altered.
SQL> exec dbms_stats.gather_table_stats('USER_OWNER','T_TEST_TAB1',cascade => true);
PL/SQL procedure successfully completed.
SQL> select col1 from t_test_tab1;
99999 rows selected.
Execution Plan
Plan hash value: 2995826579
| Id | Operation            | Name           | Rows | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT     |                | 99999 |   488K|    59   (2)| 00:00:01 |
|   1 | INDEX FAST FULL SCAN| PK_T_TEST_TAB1 | 99999 |   488K|    59   (2)| 00:00:01 |
Statistics
          1 recursive calls
          0 db block gets
       6867 consistent gets
          0 physical reads
          0 redo size
    1829388 bytes sent via SQL*Net to client
      73850 bytes received via SQL*Net from client
       6668 SQL*Net roundtrips to/from client
          0 sorts (memory)
          0 sorts (disk)
      99999 rows processed
SQL> If you see here the even though statistics were gathered,
     * In the 1st table T_TEST_TAB, the table is still using FULL table access after creation of index.
     * And in the 2nd table T_TEST_TAB1, table is using PRIMARY KEY as expected.
Any comments ??
Regards,
BPat

Thanks.
Yes, ignored the NOT NULL part.Did a test and now it is working as expected
SQL> create table t_test_tab(col1 number not null, col2 number, col3 varchar2(12));
Table created.
SQL>
create sequence seq_t_test_tab start with 1 increment by 1 ;SQL>
Sequence created.
SQL> insert into t_test_tab select seq_t_test_tab.nextval, round(dbms_random.value(1,999)) , 'B'||round(dbms_random.value(1,50))||'A' from dual connect by level < 100000;
99999 rows created.
SQL> commit;
Commit complete.
SQL> exec dbms_stats.gather_table_stats('GREP_OWNER','T_TEST_TAB',cascade => true);
PL/SQL procedure successfully completed.
SQL> set autotrace traceonly
SQL> select col1 from t_test_tab;
99999 rows selected.
Execution Plan
Plan hash value: 1565504962
| Id | Operation         | Name       | Rows | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT |            | 99999 |   488K|    74   (3)| 00:00:01 |
|   1 | TABLE ACCESS FULL| T_TEST_TAB | 99999 |   488K|    74   (3)| 00:00:01 |
Statistics
          1 recursive calls
          0 db block gets
       6912 consistent gets
          0 physical reads
          0 redo size
    1829388 bytes sent via SQL*Net to client
      73850 bytes received via SQL*Net from client
       6668 SQL*Net roundtrips to/from client
          0 sorts (memory)
          0 sorts (disk)
      99999 rows processed
SQL> create index idx_t_test_tab on t_test_tab(col1);
Index created.
SQL> exec dbms_stats.gather_table_stats('GREP_OWNER','T_TEST_TAB',cascade => true);
PL/SQL procedure successfully completed.
SQL> select col1 from t_test_tab;
99999 rows selected.
Execution Plan
Plan hash value: 4115006285
| Id | Operation            | Name           | Rows | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT     |                | 99999 |   488K|    63   (2)| 00:00:01 |
|   1 | INDEX FAST FULL SCAN| IDX_T_TEST_TAB | 99999 |   488K|    63   (2)| 00:00:01 |
Statistics
          1 recursive calls
          0 db block gets
       6881 consistent gets
          0 physical reads
          0 redo size
    1829388 bytes sent via SQL*Net to client
      73850 bytes received via SQL*Net from client
       6668 SQL*Net roundtrips to/from client
          0 sorts (memory)
          0 sorts (disk)
      99999 rows processed
SQL>

Is their a difference between primary key and unique key with not null valu

What is the difference in having a column as primary key and having unique key with not null for the column.
vinodh

SBH wrote:
For quick review, below is the link
http://www.dba-oracle.com/data_warehouse/clustered_index.htm
You appear to have stumbled on a site that is a mine of disinformation about Oracle.
>
It would be helpful, if you explain it too..thnx !!
The site is wrong and makes up its own terminology as it goes along.
If the value for clustering factor approaches the number of blocks in the base table, then the index is said to be clustered. http://www.oracle.com/pls/db112/search?remark=quick_search&word=clustered+index
There is no create clustered index in Oracle.
- Clustering factor affects the efficiency of an index.
- There can be clustered tables that you can create indexes on.
- An Index Organized table is a similar concept to the Microsoft SQL Server clustered index, but it isn't the same thing at all.

Difference between Primary Key and Unique Key with NOT NULL constraint

As both can be referred to another table.
Apart from the difference that Primary Key can be only 1 and Unique keys can be multiple,
is there any difference?
Like in terms of type of Index?

PARAG_C wrote:
As both can be referred to another table.
Apart from the difference that Primary Key can be only 1 and Unique keys can be multiple,
is there any difference?
Like in terms of type of Index?Technically there is almost no difference. Logically the two are often used for slightly different concepts.
The PK (and with it the index) is often an ID column filled by a seqeunce. This key can then be refenced by foreign key constraints on other tables. it is very useful to have this as a meaningless technical construct. Because then the chance that such a ID needs to be changed is extremly slim.
The UK (and with it the index) is often one or several columns that represent the logical key for the entity. Foreign key constriants should not point to this. THe chance that this attribute will be changed at some point in time is way higher then for a meaningless number (ID).

Difference between Primary Key and Unique+Not NUll

Hi Guys,
Is there any difference the column being declared as primary key or unique+NOT NULL.
Please let me know the internal and application point of view.
Thanks in advance!
Ranjan

957590 wrote:
Ok,Thanks however I donot think Primary key uses unique indexPK uses whatever index you specify - unique or not (as long as index is on proper column(s)). However, if you do not specify any index, PK creates unique index:
SQL> create table tbl(
2                   id number,
3                   name varchar2(10)
4                  )
5 /
Table created.
SQL> alter table tbl
2    add constraint tbl_pk
3      primary key(
4                  id
5                 )
6 /
Table altered.
SQL> select index_name,
2          uniqueness
3    from user_indexes
4    where table_name = 'TBL'
5 /
INDEX_NAME                     UNIQUENES
TBL_PK                         UNIQUE
SQL> select constraint_name,
2          index_name
3    from user_constraints
4    where table_name = 'TBL'
5 /
CONSTRAINT_NAME                INDEX_NAME
TBL_PK                         TBL_PK
SQL> alter table tbl
2    drop primary key
3 /
Table altered.
SQL> create index tbl_non_unique_pk_index
2    on tbl(
3           id
4          )
5 /
Index created.
SQL> alter table tbl
2    add constraint tbl_pk
3      primary key(
4                  id
5                 )
6        using index tbl_non_unique_pk_index
7 /
Table altered.
SQL> select index_name,
2          uniqueness
3    from user_indexes
4    where table_name = 'TBL'
5 /
INDEX_NAME                     UNIQUENES
TBL_NON_UNIQUE_PK_INDEX        NONUNIQUE
SQL> select constraint_name,
2          index_name
3    from user_constraints
4    where table_name = 'TBL'
5 /
CONSTRAINT_NAME                INDEX_NAME
TBL_PK                         TBL_NON_UNIQUE_PK_INDEX
SQL> insert
2    into tbl
3    values(
4           1,
5           'A'
6          )
7 /
1 row created.
SQL> insert
2    into tbl
3    values(
4           2,
5           'B'
6          )
7 /
1 row created.
SQL> insert
2    into tbl
3    values(
4           1,
5           'C'
6          )
7 /
insert
ERROR at line 1:
ORA-00001: unique constraint (SCOTT.TBL_PK) violated
SQL> SY.

What is difference between sy-tabix and sy-index.

SAP Seniors,
Can you please let me know what is difference between sy-index and sy-tabix.
I read the SAP help, it is confusing for me. it looks like both are same from help. please help me.
Thank you
Anitha.

HI,
Here is a brief description of difference between SY_TABIX and SY_INDEX and using them with several conditions.
SY-TABIX
Current line of an internal table. SY-TABIX is set by the statements below, but only for index tables. The field is either not set or is set to 0 for hashed tables.
APPEND sets SY-TABIX to the index of the last line of the table, that is, it contains the overall number of entries in the table.
COLLECT sets SY-TABIX to the index of the existing or inserted line in the table. If the table has the type HASHED TABLE, SY-TABIX is set to 0.
LOOP AT sets SY-TABIX to the index of the current line at the beginning of each loop lass. At the end of the loop, SY-TABIX is reset to the value that it had before entering the loop. It is set to 0 if the table has the type HASHED TABLE.
READ TABLE sets SY-TABIX to the index of the table line read. If you use a binary search, and the system does not find a line, SY-TABIX contains the total number of lines, or one more than the total number of lines. SY-INDEX is undefined if a linear search fails to return an entry.
SEARCH <itab> FOR sets SY-TABIX to the index of the table line in which the search string is found.
SY-INDEX
In a DO or WHILE loop, SY-INDEX contains the number of loop passes including the current pass.
Hope this helps.
Thank you,
Pavan.

What is the difference between "Invisible" (11g) and "virtual" index?

Hi
What is the difference between the "Invisible" index and "virtual" index?
Thanks
Balaji

Indexes can be visible or invisible. An invisible index is maintained by DML operations and cannot be used by the optimizer. Actually takes space, but is not to be used as part of a potential access path.
AFAIK, a virtual index is created by the tools used in SQL statement access path tuning to provide an alternative for the optimizer to test. It does not take any real space as it is a pure in memory definition.

Difference between unique constraint and unique index

1. What is the difference between unique constraint and unique index when unique constraint is always indexed ? Which one is better in this case for better performance ?
2. Is Composite index of 3 columns x,y,z better
or having independent/ seperate indexes on 3 columns x,y,z is better for better performance ?
3. It has been very confusing for me to decide which columns to index, I have indexed most foreignkey columns, is it a good idea ? We do lot of selects and DMLS on most of our tables. Is there any query that I can run and find out if indexes are really being used and if they are improving any performance. I have analyzed and computed my indexes using ANALYZE index index_name validate structure and COMPUTE STATISTICS;
null

1. Unique index is part of unique constraint. Of course you can create standalone unique index. But is is no point to skip the logical view of business if you spend same effort to achive.
You create unique const. Oracle create the unique index for you. You may specify index characteristic in unique constraint.
2. Depends. You can't utilize the composite index if the searching condition is not whole or front part of the indexing key. You can't utilize your index if you query the table for y=2. That is.
3. As old words in database arena, Index may be good or bad for a table depending on the size of table, number of columns in the table... etc. It is very environmental dependent. In fact, It is part of database nomalization. Statistic is a way oracle use to determine the execution plan.
Steve
null

Difference between Unique key and Primary key(other than normal difference)

Hello,
1).Can any one tell me any other difference between Unique key and Primary key other than it having NULLs.
2). What is the difference the words 'DISTINCT' and 'UNIQUE' in a sql query.
Thanks in advance.

Hi
If you don't believe me than see the documentation in
OTN.
Ott Karesz
http://www.trendo-kft.hu
SQL> create table scott.tbl_clob
2 (sss CLOB)
3 /
Tabelle wurde angelegt.
SQL> insert into scott.tbl_clob values('wrwrwrw')
2 /
1 Zeile wurde erstellt.
SQL> insert into scott.tbl_clob values('wrwrwrw')
2 /
1 Zeile wurde erstellt.
SQL> select distinct sss from scott.tbl_clob
2 /
select distinct sss from scott.tbl_clob
FEHLER in Zeile 1:
ORA-00932: nicht übereinstimmende Datentypen
SQL> select unique sss from scott.tbl_clob
2 /
select unique sss from scott.tbl_clob
FEHLER in Zeile 1:
ORA-00932: nicht übereinstimmende Datentypen
SQL> select distinct to_char(sss) from scott.tbl_clob
2 /
TO_CHAR(SSS)
wrwrwrw
SQL> select unique to_char(sss) from scott.tbl_clob
2 /
TO_CHAR(SSS)
wrwrwrw
SQL>

Is there any performance difference between unique and no unique index

Hi,
We are working with both databases Oracle and MS-SQL and we have an open channel to MS-SQL server core team.
We got the word from them that there is a difference between unique and no unique index from the optimizer perspective, i.e. the optimizer knowing that the index is unique may choose a more suitable plan for running a specific query, we're still trying to find a specific example.
Anyway, since we do not have an open channel to Oracle core, I thought maybe one of you guys knows something about Oracle optimizer behavior on this issue.
I am interested verified answers from certified sources and not suggestions or thoughts.
Thanks in advanced,
Tal ([email protected]).

Maybe, you will like to check this link for a similar question answered by Tom Kyte
http://asktom.oracle.com/pls/ask/f?p=4950:8:385900000490041683::NO::F4950_P8_DISPLAYID,F4950_P8_CRITERIA:7641143144618,

Difference between Unique key and Unique index

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