this question is for performance issue,
For example, if I would add a unique constraint such as:
ALTER TABLE Staffs ADD CONSTRAINT test UNIQUE (Company_Name, Staff_ID);
should I add a unique index for performance issue?
CREATE UNIQUE INDEX test2 ON Staffs (Company_Name, Staff_ID);
For Primary key, I can see there must be a corresponding index in dba_indexes system table,
but I have not seen the equivalent for the case unique constraint
"I have not seen the equivalent for the case unique constraint"
Hmmmm, are you sure?
SQL> create table t23
2 (id number
3 , col1 date)
4 /
Table created.
SQL> alter table t23
2 add constraint t23_uk unique (id)
3 /
Table altered.
SQL> select index_name, uniqueness
2 from user_indexes
3 where table_name='T23'
4 /
INDEX_NAME UNIQUENES
------------------------------ ---------
T23_UK UNIQUE
SQL>
Note that we can use an existing index, and it doesn't have to be unique. But this means the index name might not match the constraint name (this would also work for primary keys):
SQL> alter table t23 drop constraint t23_uk;
Table altered.
SQL> select index_name, uniqueness
2 from user_indexes
3 where table_name='T23'
4 /
no rows selected
SQL> create index t23_idx on t23(id)
2 /
Index created.
SQL> select index_name, uniqueness
2 from user_indexes
3 where table_name='T23'
4 /
INDEX_NAME UNIQUENES
------------------------------ ---------
T23_IDX NONUNIQUE
SQL> alter table t23
2 add constraint t23_uk unique (id)
3 /
Table altered.
SQL>
Does the non-unique index enforce the unique constraint? Yes it does:
SQL> insert into t23 values (1, sysdate)
2 /
1 row created.
SQL> r
1* insert into t23 values (1, sysdate)
insert into t23 values (1, sysdate)
*
ERROR at line 1:
ORA-00001: unique constraint (APC.T23_UK) violated
SQL> drop index t23_idx
2 /
drop index t23_idx
*
ERROR at line 1:
ORA-02429: cannot drop index used for enforcement of unique/primary key
SQL>
We can check the data dictionary to see which index is associated with a constraint:
SQL> select constraint_name, constraint_type, index_name
2 from user_constraints
3 where table_name = 'T23'
4 /
CONSTRAINT_NAME C INDEX_NAME
------------------------------ - ------------------------------
T23_UK U T23_IDX
SQL>
Related
I am trying to Create a list partition Based on the column "REFRESH_FLAG_Y" which has only Y and N as its Values, Below is the Alter Table used to Create the partition
ALTER TABLE "EDW"."LABOR_SCHEDULE_DAY_F" MODIFY
PARTITION BY LIST ("REFRESH_FLAG")
(PARTITION "REFRESH_FLAG_Y" VALUES ('Y') ,
PARTITION "REFRESH_FLAG_N" VALUES ('N')) ;
COMMIT;
But Whenever I execute the code I get an Error message
ERROR at line 1:
ORA-14400: inserted partition key does not map to any partition
You did tag the question with Oracle 11g tag; do you really use it?
This is a 12c example; it works if everything is OK:
SQL> create table labor_schedule_day_f as
2 select 1 id, 'Y' refresh_flag from dual union all
3 select 2 id, 'N' refresh_flag from dual;
Table created.
SQL> alter table labor_schedule_Day_f modify
2 partition by list (refresh_flag)
3 (partition refresh_flag_y values ('Y'),
4 partition refresh_flag_n values ('N')
5 );
Table altered.
Error you reported means this:
SQL> drop table labor_schedule_day_f;
Table dropped.
SQL> create table labor_schedule_day_f as
2 select 1 id, 'Y' refresh_flag from dual union all
3 select 2 id, 'N' refresh_flag from dual;
Table created.
Insert a row whose REFRESH_FLAG isn't Y nor N (so it violates the rule you specified):
SQL> insert into labor_schedule_day_f values (3, 'X');
1 row created.
Using the same ALTER TABLE statement as previously:
SQL> alter table labor_schedule_Day_f modify
2 partition by list (refresh_flag)
3 (partition refresh_flag_y values ('Y'),
4 partition refresh_flag_n values ('N')
5 );
alter table labor_schedule_Day_f modify
*
ERROR at line 1:
ORA-14400: inserted partition key does not map to any partition
SQL>
See? Error you got, which means that
which has only Y and N as its Values
isn't true.
P.S. You'd get the same result even if refresh_flag was NULL for some rows.
as my title, I want to change my identity column by sequence to GENERATED ALWAYS.
For ex, I have a table like this:
CREATE SEQUENCE DPT.Deposit_SEQ
START WITH 1
INCREMENT BY 10
NOCACHE
NOCYCLE;
CREATE TABLE DPT.TEST(
Id NUMBER(10)DEFAULT DPT.Deposit_SEQ.nextval NOT NULL
,Code VARCHAR2(20),
CONSTRAINT PK_TEST PRIMARY KEY (ID)
);
Insert into DPT.TEST (ID, CODE) values (1,'ABC');
COMMIT;
Now, I want to change from sequence to GENERATED ALWAYS like this:
Id NUMBER(10) GENERATED ALWAYS AS IDENTITY START WITH 6
INCREMENT BY 10
NOCACHE
NOCYCLE;
I tried by create one more column and drop old column but failed. How can I do that?
Thanks!
"But failed" is not an Oracle error and is difficult to debug.
Anyway, it works for me:
Create table and a sequence, insert some rows:
SQL> CREATE SEQUENCE Deposit_SEQ START WITH 1 INCREMENT BY 10 NOCACHE NOCYCLE;
Sequence created.
SQL> CREATE TABLE TEST
2 (
3 Id NUMBER (10) DEFAULT Deposit_SEQ.NEXTVAL NOT NULL,
4 Code VARCHAR2 (20),
5 CONSTRAINT PK_TEST PRIMARY KEY (ID)
6 );
Table created.
SQL>
SQL> INSERT INTO TEST (ID, CODE)
2 VALUES (1, 'ABC');
1 row created.
SQL> INSERT INTO TEST (ID, CODE)
2 VALUES (3, 'DEF');
1 row created.
SQL> SELECT * FROM test;
ID CODE
---------- --------------------
1 ABC
3 DEF
Drop current primary key column (ID) and add a new, identity column:
SQL> ALTER TABLE test
2 DROP COLUMN id;
Table altered.
SQL> ALTER TABLE test
2 ADD id NUMBER GENERATED ALWAYS AS IDENTITY START WITH 6;
Table altered.
SQL> SELECT * FROM test;
CODE ID
-------------------- ----------
ABC 6
DEF 7
SQL> ALTER TABLE test ADD CONSTRAINT pk_test PRIMARY KEY (id);
Table altered.
SQL>
As you can see, no problem.
Is there any ways to add autoincrement to primary key in already existing table in Oracle 12c. May be with ALTER TABLE function or smth, I mean without triggers and sequences.
As far as I can tell, you can not "modify" existing primary key column into a "real" identity column.
If you want to do that, you'll have to drop the current primary key column and then alter table and add a new identity column.
Workaround is to use a sequence (or a trigger), but - you said you don't want to do that. Anyway, if you decide to use it:
SQL> create table test
2 (id number constraint pk_test primary key,
3 name varchar2(10));
Table created.
SQL> insert into test values (1, 'LF');
1 row created.
SQL> create sequence seq_test start with 2;
Sequence created.
SQL> alter table test modify id default seq_test.nextval;
Table altered.
SQL> insert into test (name) values ('BF');
1 row created.
SQL> select * from test;
ID NAME
---------- ----------
1 LF
2 BF
SQL>
Or, with dropping current primary key column (note that it won't work easy if there are foreign keys involved):
SQL> alter table test drop column id;
Table altered.
SQL> alter table test add id number generated always as identity;
Table altered.
SQL> select * From test;
NAME ID
---------- ----------
LF 1
BF 2
SQL> insert into test (name) values ('test');
1 row created.
SQL> select * From test;
NAME ID
---------- ----------
LF 1
BF 2
test 3
SQL>
I have a table with data and need to remove a column, which is marked as unused. But it gives the error due to the compressed table.
I have used the command
ALTER TABLE <table name> MOVE NOCOMPRESS NOLOGGING PARALLEL 4;
But it gives this error:
ORA-14511: cannot perform operation on a partitioned object
How can I disable the partitioned? And how can I remove the unused column?
No, you cannot move partitioned table with one alter table statement, you need to perform relocation of that table into a new segment partition by partition:
Create test table:
SQL> create table t1(
2 col1 number,
3 col2 number
4 )
5 partition by range(col1) (
6 partition p_1 values less than (10) compress,
7 partition p_2 values less than (20) compress
8 );
Table created.
Populate test table with some sample data:
SQL> insert into t1(col1, col2)
2 select level
3 , level
4 from dual
5 connect by level <= 3;
3 rows created.
SQL> commit;
Commit complete.
SQL> select * from t1;
COL1 COL2
---------- ----------
1 1
2 2
3 3
Drop column statement fails:
SQL> alter table t1 drop column col2;
alter table t1 drop column col2
*
ERROR at line 1:
ORA-39726: unsupported add/drop column operation on compressed tables
Table relocation fails:
SQL> alter table t1 move nocompress;
alter table t1 move nocompress
*
ERROR at line 1:
ORA-14511: cannot perform operation on a partitioned object
Perform relocation of each partition:
SQL> alter table t1 move partition p_1 nocompress;
Table altered.
SQL> alter table t1 move partition p_2 nocompress;
Table altered.
When there are too many partitions, you can easily generate alter table statements while querying user_tab_partitions data dictionary view. For example:
SQL> column res format a50
SQL> select 'alter table ' || t.table_name ||
2 ' move partition ' || t.partition_name ||
3 ' nocompress;' as res
4 from user_tab_partitions t
5 where t.table_name = 'T1';
RES
--------------------------------------------------
alter table T1 move partition P_1 nocompress;
alter table T1 move partition P_2 nocompress;
After you have moved all partitions with nocompress option, you can drop column(s) issuing:
alter table t1 drop column col2
statement, or
alter table t1 drop unused columns
statement, if you already marked column(s) as unused before relocation.
Dropping unused columns:
Make col2 unused
SQL> alter table t1 set unused(col2);
Table altered.
List tables with unused columns in our schema
SQL> column table_name format a5
SQL> column table_name format a5
SQL> select *
2 from user_unused_col_tabs;
TABLE COUNT
----- ----------
T1 1
Relocate partitions
SQL> alter table T1 move partition P_1 nocompress;
Table altered.
SQL> alter table T1 move partition P_2 nocompress;
Table altered.
Drop unused columns:
SQL> alter table t1 drop unused columns;
Table altered.
Make sure we dropped everything we wanted to drop. Col2 is gone:
SQL> desc t1;
Name Null? Type
-------- -------- -----------
COL1 NUMBER
There are no tables with unused columns:
SQL> select *
2 from user_unused_col_tabs;
no rows selected
I need to create a sequence and a trigger to auto-increment the primary key on a table but I have no idea on how to do it.
Create the table and the sequence
SQL> create table staff (
2 emp_id number primary key,
3 staff_name varchar2(100)
4 );
Table created.
SQL> create sequence emp_id_seq;
Sequence created.
Now, you can create a trigger that uses the sequence to populate the primary key
SQL> create trigger trg_emp_id
2 before insert on staff
3 for each row
4 begin
5 select emp_id_seq.nextval
6 into :new.emp_id
7 from dual;
8 end;
9 /
Trigger created.
Now, when you insert data, you woon't need to specify the EMP_ID column-- it will automatically be populated by the trigger
SQL> insert into staff( staff_name ) values ('Justin');
1 row created.
SQL> select * from staff;
EMP_ID STAFF_NAME
---------- --------------------
1 Justin
Read this, Beautiful article.
how sequence [auto increment in oracle]
syntax
Create sequence sequence_name
start with value
increment by value
minvalue value
maxvalue value;
example
SQL> create table emp (
emp_id number(10),
fname varchar2(25),
lname varchar2(25),
constraint pk_emp_id PRIMARY KEY(emp_id)
);
SQL> Create sequence emp_sequence
start with 1
increment by 1
minvalue 1
maxvalue 10000;
SQL> insert into emp (emp_id,fname,lname) values(emp_sequence.nextval,'Darvin','Johnson');
SQL> insert into emp (emp_id,fname,lname) values(emp_sequence.nextval,'Mig','Andrews');
SQL> insert into emp (emp_id,fname,lname) values(emp_sequence.nextval,'Alex','Martin');
SQL> insert into emp (emp_id,fname,lname) values(emp_sequence.nextval,'Jon','paul');
SQL> insert into emp (emp_id,fname,lname) values(emp_sequence.nextval,'Yatin','Bones');
in emp_sequence.nextval where emp_sequence is the name of sequence we created above and nextval is a function that is used to assign the next number from emp_sequence to emp_id column in emp table.
SQL> select * from emp;
EMP_ID FNAME LNAME
---------- ------------------------- -------------------------
1 Darvin Johnson
2 Mig Andrews
3 Alex Martin
4 Jon paul
5 Yatin Bones
Try this:
create sequence seq_EmpID start with 1 increment by 1
insert into Emp_Table values(seq_EmpID.nextval,'Ram')
I am not sure which version of Oracle you are using, but the following will work in 19c:
create table staff (
emp_id NUMBER GENERATED BY DEFAULT ON NULL AS IDENTITY PRIMARY KEY,
staff_name varchar2(100)
);
https://docs.oracle.com/en/database/other-databases/nosql-database/19.3/java-driver-table/creating-tables-identity-column.html
The command above creates a system sequence that is automatically employed to populate the key value. you cannot drop the sequence created as it is a system sequence, but because of the dependency on the column when the table is dropped and the recycle bin purged it is removed.
Very good question!!
Probably sequence can be used in this way - also, I am not sure if there really is a difference :
CREATE SEQUENCE emp_id_seq MINVALUE 1 START WITH 1 INCREMENT BY 1 CACHE 10;
First creating the table :
sql-> create table item(id int primary key, name varchar(25),qty int, price int);
Now we want to make auto increment sequence to the first column i.e. id
sql-> CREATE SEQUENCE id MINVALUE 1 START WITH 1 CACHE 10; //system saves the last 10 items in temp memory
This will create auto increment.
Now we are inserting data:
sql-> insert into item VALUES(id.nextval,'ddcd',2,4);
sql-> insert into item VALUES(id.nextval,'ddcd',676,4);
Finally Displaying the table :
SQL> select * from item;
ID NAME QTY PRICE
1 ddcd 2 4
2 ddcd 676 4
If you use a sequence for several tables, because the value of the sequence is inconsistent example:
we have two tables emp and depeartement:
If I use the sequence on emp I would have: ID_dept = 6 because the 5 is already used in the other table.
example :
SQL> insert into emp values(masequence.nextval,'aaa');
1 ligne crÚÚe.
SQL> insert into departement values(masequence.nextval,'aaa');
1 ligne crÚÚe.
SQL> select * from emp;
ID_EMP NOM_EMP
---------- -------------------------
5 aaa
SQL> select * from departement;
ID_DEPT NOM_DEPT
---------- ----------
6 aaa
SQL>