I have an initialization script I use on Spring Boot application start and I create the table if it doesn't exist. Then I delete all the data from the table and execute a bunch on inserts.
create table if not exists employee (
id serial primary key,
name varchar(255)
);
delete from employee;
-- inserts
With each execution of the script, the sequence still continues, so the new rows don't start from one. I have to reset such sequence too, however, it is generated and I dont know its name unless I call this script:
select pg_get_serial_sequence('employee', 'id');
-- returns public.employee_id_seq
I tried to combine it together and reset the sequence based on the output of this funciton, but with no luck. How to reset the generated sequence without knowing its name? My attempt so far cannot resolve the seq sequence from the variable:
do $$
declare
seq varchar(255);
begin
select pg_get_serial_sequence('employee', 'employee_id') into seq;
alter sequence seq restart with 1;
end; $$;
The simplest solution is to use truncate table . . . restart identity instead of delete:
truncate table employee restart identity;
Here is a db<>fiddle.
Truncate table is recommended for other reasons too. For instance, it reclaims the space the table used immediately. And it is much faster. The one difference is that delete triggers are not called (although your table doesn't have any triggers).
It is basically a bad idea to reset a id serial to any number, so you must be very carefully using the following.
especially when you have foreign keys to the id firld
the camand you are looking for is
ALTER SEQUENCE <table_name>_<id_column>_seq RESTART WITH 1
create table if not exists employee (
id serial primary key,
name varchar(255)
);
INSERT INTO employee (name) VALUES ('a'),('B'),('C')
3 rows affected
delete from employee;
3 rows affected
ALTER SEQUENCE employee_id_seq RESTART WITH 1
INSERT INTO employee (name) VALUES ('a')
1 rows affected
SELECT * FROM employee
id | name
-: | :---
1 | a
db<>fiddle here
Related
I was wondering how can I add an identity column to existing oracle table? I am using oracle 11g. Suppose I have a table named DEGREE and I am going to add an identity column to that.
FYI table is not empty.
You can not do it in one step. Instead,
Alter the table and add the column (without primary key constraint)
ALTER TABLE DEGREE ADD (Ident NUMBER(10));
Fill the new column with data which will fulfill the primary key constraint (unique/not null), e.g. like
UPDATE DEGREE SET Ident=ROWNUM;
Alter the table and add the constraint to the column
ALTER TABLE DEGREE MODIFY (Ident PRIMARY KEY);
After that is done, you can set up a SEQUENCE and a BEFORE INSERT trigger to automatically set the id value for new records.
From Oracle 12c you would use an identity column.
For example, say your table is called demo and has 3 columns and 100 rows:
create table demo (col1, col2, col3)
as
select dbms_random.value(1,10), dbms_random.value(1,10), dbms_random.value(1,10)
from dual connect by rownum <= 100;
You could add an identity column using:
alter table demo add demo_id integer generated by default on null as identity;
update demo set demo_id = rownum;
Then reset the internal sequence to match the data and prevent manual inserts:
alter table demo modify demo_id generated always as identity start with limit value;
and define it as the primary key:
alter table demo add constraint demo_pk primary key (demo_id);
This leaves the new column at the end of the column list, which shouldn’t normally matter (except for tables with a large number of columns and row chaining issues), but it looks odd when you describe the table. However, we can at least tidy up the dictionary order using the invisible/visible hack:
SQL> desc demo
Name Null? Type
-------------------------------- -------- ----------------------
COL1 NUMBER
COL2 NUMBER
COL3 NUMBER
DEMO_ID NOT NULL NUMBER(38)
begin
for r in (
select column_name from user_tab_columns c
where c.table_name = 'DEMO'
and c.column_name <> 'DEMO_ID'
order by c.column_id
)
loop
execute immediate 'alter table demo modify '||r.column_name||' invisible';
execute immediate 'alter table demo modify '||r.column_name||' visible';
end loop;
end;
/
SQL> desc demo
Name Null? Type
-------------------------------- -------- ----------------------
DEMO_ID NOT NULL NUMBER(38)
COL1 NUMBER
COL2 NUMBER
COL3 NUMBER
One thing you can't do (as of Oracle 18.0) is alter an existing column to make it into an identity column, so you have to either go through a process like the one above but copying the existing values and finally dropping the old column, or else define a new table explicitly with the identity column in place and copy the data across in a separate step. Otherwise you'll get:
-- DEMO_ID column exists but is currently not an identity column:
alter table demo modify demo_id generated by default on null as identity start with limit value;
-- Fails with:
ORA-30673: column to be modified is not an identity column
add the column
alter table table_name add (id INTEGER);
create a sequence table_name_id_seq with start with clause, using number of rows in the table + 1 or another safe value(we don't want duplicate ids);
lock the table (no inserts)
alter table table_name lock exclusive mode;
fill the column
update table_name set id = rownum; --or another logic
add a trigger to automaticaly put the id on insert using the sequence(you can find examples on internet, for example this answer)
When you'll fire the create trigger the lock will be released. (it automatically commits).
Also, you may add unique constraint on the id column, it is best to do so.
For Oracle :
CREATE TABLE new_table AS (SELECT ROWNUM AS id, ta.* FROM old_table ta)
remember this id column is not auto incremented
I am using PGsql and transferred some data from another database into my new one. The table has records starting at PK 200. The tables primary key (bigint - autoincrementing) is currently starting at 0. If I continue to insert records, eventually it will reach 200. My question is, will these records create an issue when trying to insert record 200? or will PGsql know the conflict, then find the next available AI index (say 234)?
Thanks! If it will cause a conflict, how can I set the current index of my table to the last index of data? (like 234).
My question is, will these records create an issue when trying to insert record 200?
Assuming that you have a serial column or the-like: yes, this will create an issue. The serial has no knowledge that some sequences are not available, sp this will result in a duplicate key error. Meanwhile the sequence increments also on such errors, and the next call will return the next number, and so on.
This is easily reproducible:
create table t (id serial primary key, val text);
insert into t (id, val) values (2, 'blocker');
-- 1 rows affected
insert into t (val) values ('foo');
-- 1 rows affected
insert into t (val) values ('bar');
-- ERROR: duplicate key value violates unique constraint "t_pkey"
-- DETAIL: Key (id)=(2) already exists.
insert into t (val) values ('baz');
-- 1 rows affected
select * from t order by id;
id | val
-: | :------
1 | foo
2 | blocker
3 | baz
One solution is to reset the sequence: the only safe starting point is the high watermark of the table:
select setval(
't_id_seq',
coalesce((select max(id) + 1 from t), 1),
false
);
Demo on DB Fiddlde: you can uncomment the setval() statement to see how it avoids the error.
I am restoring the data of a truncated table in an Oracle Database from an exported csv file. However, I find that the primary key auto-increments and does not insert the actual values of the primary key constrained column from the backed up file.
I intend to do the following:
1. drop the primary key
2. import the table data
3. add primary key constraints on the required column
Is this a good approach? If not, what is recommended? Thanks.
EDIT: After more investigation, I observed there's a trigger to generate nextval on a sequence to be inserted into the primary key column. This is the source of the predicament. Hence, following the procedure above would not solve the problem. It lies in the trigger (and/or sequence) on the table. This is solved!
easier to use your .csv as an external table and then go
create table your_table_temp as select * from external table
examine the data in the new temp table to ensure you know what range of primary keys is present
do a merge into the new table
samples from here and here
CREATE TABLE countries_ext (
country_code VARCHAR2(5),
country_name VARCHAR2(50),
country_language VARCHAR2(50)
)
ORGANIZATION EXTERNAL (
TYPE ORACLE_LOADER
DEFAULT DIRECTORY ext_tab_data
ACCESS PARAMETERS (
RECORDS DELIMITED BY NEWLINE
FIELDS TERMINATED BY ','
MISSING FIELD VALUES ARE NULL
(
country_code CHAR(5),
country_name CHAR(50),
country_language CHAR(50)
)
)
LOCATION ('Countries1.txt','Countries2.txt')
)
PARALLEL 5
REJECT LIMIT UNLIMITED;
and the merge
MERGE INTO employees e
USING hr_records h
ON (e.id = h.emp_id)
WHEN MATCHED THEN
UPDATE SET e.address = h.address
WHEN NOT MATCHED THEN
INSERT (id, address)
VALUES (h.emp_id, h.address);
Edit: after you have merged the data you can drop the temp table and the result is your previous table with the old data and the new data together
Edit you mention " During imports, the primary key column does not insert from the file, but auto-increments". This can only happen when there is a trigger on the table, likely, Before insert on each row. Disable the trigger and then do your import. Re-enable the trigger after committing your inserts.
I used the following procedure to solve it:
drop trigger trigger_name
Imported the table data into target table
drop sequence sequence_name
CREATE SEQUENCE SEQ_NAME INCREMENT BY 1 START WITH start_index_for_next_val MAXVALUE max_val MINVALUE 1 NOCYCLECACHE 20 NOORDER
CREATE OR REPLACE TRIGGER "schema_name"."trigger_name"
before insert on target_table
for each row
begin
select seq_name.nextval
into :new.unique_column_name
from dual;
end;
I would like to link several sequences for generating default values for several columns of a table.
For example:
CREATE SEQUENCE seq1 START WITH 1;
CREATE SEQUENCE seq2 START WITH 1;
CREATE TABLE mytable (rid int GENERATED BY DEFAULT AS SEQUENCE seq1 PRIMARY KEY, p63 int GENERATED BY DEFAULT AS SEQUENCE seq2)
Unfortunately, an error is occured: "identity definition not allowed"
In Postgresql is working.
Any idea ?
Thanks
The first use of the sequence is allowed. You can write a BEFORE INSERT TRIGGER to insert sequence values into the second column.
Having the same issue, I came upon this post. I used another workaround :
CREATE SEQUENCE seq1 START WITH 1;
CREATE SEQUENCE seq2 START WITH 1;
CREATE TABLE mytable (
rid int DEFAULT nextval('seq1') NOT NULL,
p63 int NOT NULL
);
ALTER TABLE mytable ALTER p63 SET DEFAULT NEXTVAL('seq2');
Altering the p63 column after table creation made possible to use the seq2 sequence while it was not accepted when creating the table.
I had created a new table named USERLOG with two fields from a previous VIEW. The table already consist of about 9000 records. The two fields taken from the VIEW, i.e. weblog_views consist of IP (consists of IP address), and WEB_LINK (consists of URL). This is the code I used,
CREATE TABLE USERLOG
AS
SELECT C_IP, WEB_LINK FROM weblog_views;
I want to add another column to this table called the USER_ID, which would consists of a sequence starting with 1 to 9000 records to create a unique id for each existing rows. I need help with this part. I'm using Oracle SQL Developer: ODMiner version 3.0.04.
I tried using the AUTO-INCREMENT option,
ALTER TABLE USERLOG
ADD USER_ID INT UNSIGNED NOT NULL AUTO_INCREMENT;
But I get an error with this,
Error report:
SQL Error: ORA-01735: invalid ALTER TABLE option
01735. 00000 - "invalid ALTER TABLE option"
So, I would really appreciate any help that I can get!
You would need to add a column
ALTER TABLE userlog
ADD( user_id number );
create a sequence
CREATE SEQUENCE user_id_seq
START WITH 1
INCREMENT BY 1
CACHE 20;
Update the data in the table
UPDATE userlog
SET user_id = user_id_seq.nextval
Assuming that you want user_id to be the primary key, you would then add the primary key constraint
ALTER TABLE userlog
ADD CONSTRAINT pk_user_id PRIMARY KEY( user_id );
If you want to use the sequence to automatically add the user_id when you do an INSERT (the other option would be to specifically reference user_id_seq.nextval in your INSERT statements, you would also need a trigger
CREATE OR REPLACE TRIGGER trg_userlog_user_id
BEFORE INSERT ON userlog
FOR EACH ROW
BEGIN
:new.user_id := user_id_seq.nextval;
END;
In addition to Justin's excellent answer you might want to prevent NULL values for your user_id in the future (as they could still be caused by UPDATE statements). Therefore, execute the following statement at the end:
ALTER TABLE userlog MODIFY(user_id number NOT NULL);
Step 1.
Create sequence to be used by the column
eg:
CREATE SEQUENCE user_id_seq
START WITH 1
INCREMENT BY 1
CACHE 20;
Step 2.
Update new column with sequence
eg:
UPDATE userlog
SET user_id = user_id_seq.nextval;
Step 3. - Set Sequence as the default value for the column, will work only above Oracle 12c
ALTER TABLE USERLOG
MODIFY USER_ID INT DEFAULT user_id_seq.nextval;