in postgres sql creating the table as select dropped the not null constraints on the table.
for example :
create table A (char a not null);
create table B as select * from a;
select * from B;-- no constraint is copied from A table
please let me know how to copy table data as well as constraints in postgres.
There is no single-command solution to this.
To create a table based on an existing one, including all constraints, use:
create table B ( like a including constraints);
Once you have done that, you can copy the data from the old one to the new one:
insert into b
select * from a;
If you do this in a single transaction, it looks like an atomic operation to all other sessions connected to the database.
very detailed and nicely explained tutorial for create table command in PostgreSQL 9.1
http://www.postgresql.org/docs/current/static/sql-createtable.html
Not null constraints are always copied (if creating table by giving reference of parent table in create table command) and even with including constraints, only check constraint will be copied.
Related
I often see these suggestions on how to copy one table into another:
This one should create a table with the same properties (i.e. primary key and constraints), it doesn't actually work in PostgreSQL though:
CREATE TABLE New_Users LIKE Old_Users;
This one should just copy the content, and some posts (like this one)[https://stackoverflow.com/a/11433568] claim you can do it after the first command.
INSERT INTO New_Users SELECT * FROM Old_Users GROUP BY ID;
In PostgreSQL, it seems like the second command creates the table if it does not exist, and fails if the table is already there, but it indeed does not preserve the properties of the original table.
I'd like to atomically drop a table and create a new one with the same name, but with the contents and properties of another existing table. Something like this:
BEGIN;
DROP TABLE New_Users;
CREATE TABLE New_Users (LIKE Old_Users);
INSERT INTO New_Users SELECT * FROM Old_Users;
END;
This should atomically delete the current version of the table, create a skeleton with all properties and finally populate it with the content of the reference table. How can I do this in PostgreSQL?
You can use like with an option
DROP TABLE New_Users;
create table New_Users (like Old_Users including all)
or much faster
TRUNCATE New_Users RESTART IDENTITY;
INSERT INTO New_Users SELECT * FROM Old_Users;
I'm currently working on a project that uses a Redshift table with 51 columns. However, the person who made the table forgot to add a sortkey to our time column which will hurt performance for our use case if we don't add it.
How can I make a version of the table with our time column as the sortkey? I'm aware that you can't make a column a sortkey if its a member of an existing table, but I was hoping there's a way to do it that doesn't involve writing out the CREATE TABLE syntax by hand; for example, something like this would be nice:
timecube=# CREATE TABLE foo (like bar) sortkey(time);
ERROR: CREATE TABLE LIKE is not supported with DISTSTYLE, DISTKEY(), or SORTKEY() clauses
but as you can see its not supported. Is there another way? As we're still developing we don't need any of existing data.
Using traditional tools like pgdump didn't work well because they don't include any of the Redshift extras like encoding.
Redshift supports specifying the DIST and SORT keys as part of CREATE TABLE AS statements, as per the docs.
CREATE TABLE table_name
DISTSTYLE KEY
DISTKEY ( column )
SORTKEY ( column )
AS
(SELECT *
FROM source_table)
;
First step you need to do use get create table statement for existing table. Then create new table this time add sort key to new table.
Check encoding for old table ( when you load data using copy command it automatically adds compression encodings)
select "column", type, encoding
from pg_table_def where tablename = 'old_table'
When creating new table add encoding type for each column. Create table with Sort key .
Once new table is created use below command
insert into new table ( select * from old table order by time asc)
I'm trying to setup temporary tables for unit-testing purposes. So far I managed to create a temporary table which copies the structure of an existing table:
CREATE TEMP TABLE t_mytable (LIKE mytable INCLUDING DEFAULTS);
But this lacks the data from the original table. I can copy the data into the temporary table by using a CREATE TABLE AS statement instead:
CREATE TEMP TABLE t_mytable AS SELECT * FROM mytable;
But then the structure of t_mytable will not be identical, e.g. column sizes and default values are different. Is there a single statement which copies everything?
Another problem with the first query using LIKE is that the key column still references the SEQUENCE of the original table, and thus increments it on insertion. Is there an easy way to create the new table with its own sequence, or will I have to set up a new sequence by hand?
I'm using the following code to do it:
CREATE TABLE t_mytable (LIKE mytable INCLUDING ALL);
ALTER TABLE t_mytable ALTER id DROP DEFAULT;
CREATE SEQUENCE t_mytable_id_seq;
INSERT INTO t_mytable SELECT * FROM mytable;
SELECT setval('t_mytable_id_seq', (SELECT max(id) FROM t_mytable), true);
ALTER TABLE t_mytable ALTER id SET DEFAULT nextval('t_my_table_id_seq');
ALTER SEQUENCE t_mytable_id_seq OWNED BY t_mytable.id;
Postgres 10 or later
Postgres 10 introduced IDENTITY columns conforming to the SQL standard (with minor extensions). The ID column of your table would look something like:
id integer PRIMARY KEY GENERATED BY DEFAULT AS IDENTITY
Syntax in the manual.
Using this instead of a traditional serial column avoids your problem with sequences. IDENTITY columns use exclusive, dedicated sequences automatically, even when the specification is copied with LIKE. The manual:
Any identity specifications of copied column definitions will only be
copied if INCLUDING IDENTITY is specified. A new sequence is created
for each identity column of the new table, separate from the sequences
associated with the old table.
And:
INCLUDING ALL is an abbreviated form of INCLUDING DEFAULTS INCLUDING IDENTITY INCLUDING CONSTRAINTS INCLUDING INDEXES INCLUDING STORAGE INCLUDING COMMENTS.
The solution is simpler now:
CREATE TEMP TABLE t_mytable (LIKE mytable INCLUDING ALL);
INSERT INTO t_mytable TABLE mytable;
SELECT setval(pg_get_serial_sequence('t_mytable', 'id'), max(id)) FROM tbl;
As demonstrated, you can still use setval() to set the sequence's current value. A single SELECT does the trick. pg_get_serial_sequence()]6 gets the name of the sequence.
db<>fiddle here
Related:
How to reset postgres' primary key sequence when it falls out of sync?
Is there a shortcut for SELECT * FROM?
Creating a PostgreSQL sequence to a field (which is not the ID of the record)
Original (old) answer
You can take the create script from a database dump or a GUI like pgAdmin (which reverse-engineers database object creation scripts), create an identical copy (with separate sequence for the serial column), and then run:
INSERT INTO new_tbl
SELECT * FROM old_tbl;
The copy cannot be 100% identical if both tables reside in the same schema. Obviously, the table name has to be different. Index names would conflict, too. Retrieving serial numbers from the same sequence would probably not be in your best interest, either. So you have to (at least) adjust the names.
Placing the copy in a different schema avoids all of these conflicts. While you create a temporary table from a regular table like you demonstrated, that's automatically the case since temp tables reside in their own temporary schema.
Or look at Francisco's answer for DDL code to copy directly.
I need a query to create a table which is the exact replica but with different table name and without any data from the source table using a sql query!
You can try this
SELECT * INTO Table_Copy
FROM Table
where 1=2
It will create a empty table with the same structure.
SQL Server Management Studio
Object Explorer
Connect -> Your server
Databases -> Choose Database
Tables
Right Click Your Table
Script Table as -> Create To -> New Query Editor Window
Jonathan has it (upvoted), and you should probably go with that because it's more portable. I normally use something similar:
SELECT TOP 0 * INTO [New_Table] FROM [Old_Table]
I think this better expresses what you're doing, but I like Jonathan's because 'TOP 0' is SQL Server specific, and so his is more portable.
For MySQL, you can call SHOW CREATE TABLE table_name;
It will display a CREATE TABLE query. Simply change the table name in that query and you're good to go.
http://dev.mysql.com/doc/refman/5.1/en/show-create-table.html
If you use Postgresql:
CREATE TABLE LIKE table_name
http://www.postgresql.org/docs/8.1/static/sql-createtable.html
SELECT * INTO Table_Copy
FROM Table
where 1=2
This worked very well, when i tried to create a replica of the table without any data's.
SELECT * INTO Table_Copy
FROM Table
This will create a replica with the data's too.
This can help you:
CREATE TABLE foo AS SELECT...
Read more here
select * into newtablename from sourcetablename
go
truncate newtablename
go
That will result in an exact copy but it also copies the data at first which you remove with the truncate statement.
create table <new table name> as select * from <old tale name from which you would like to extract data>
It will create a new table with a different name but will copy all existing data from the old table to new table.
in postgres you can use INHERITS or LIKE keyword to make replica of a table(only copies structure of the table)
CREATE TABLE client_new (LIKE client);
or
CREATE TABLE client_new () INHERITS (client)
Use of INHERITS creates a persistent relationship between the new child table and its parent table(s). Schema modifications to the parent(s) normally propagate to children as well, and by default the data of the child table is included in scans of the parent(s).
LIKE clause specifies a table from which the new table automatically copies all column names, their data types, and their not-null constraints.Unlike INHERITS, the new table and original table are completely decoupled after creation is complete. Changes to the original table will not be applied to the new table, and it is not possible to include data of the new table in scans of the original table.
I know the statement:
create table xyz_new as select * from xyz;
Which copies the structure and the data, but what if I just want the structure?
Just use a where clause that won't select any rows:
create table xyz_new as select * from xyz where 1=0;
Limitations
The following things will not be copied to the new table:
sequences
triggers
indexes
some constraints may not be copied
materialized view logs
This also does not handle partitions
I used the method that you accepted a lot, but as someone pointed out it doesn't duplicate constraints (except for NOT NULL, I think).
A more advanced method if you want to duplicate the full structure is:
SET LONG 5000
SELECT dbms_metadata.get_ddl( 'TABLE', 'MY_TABLE_NAME' ) FROM DUAL;
This will give you the full create statement text which you can modify as you wish for creating the new table. You would have to change the names of the table and all constraints of course.
(You could also do this in older versions using EXP/IMP, but it's much easier now.)
Edited to add
If the table you are after is in a different schema:
SELECT dbms_metadata.get_ddl( 'TABLE', 'MY_TABLE_NAME', 'OTHER_SCHEMA_NAME' ) FROM DUAL;
create table xyz_new as select * from xyz where rownum = -1;
To avoid iterate again and again and insert nothing based on the condition where 1=2
Using sql developer select the table and click on the DDL tab
You can use that code to create a new table with no data when you run it in a sql worksheet
sqldeveloper is a free to use app from oracle.
If the table has sequences or triggers the ddl will sometimes generate those for you too. You just have to be careful what order you make them in and know when to turn the triggers on or off.
You can do this
Create table New_table as select * from Old_table where 1=2 ;
but be careful
The table you create does not have any Index, PK and so on like the old_table.
DECLARE
l_ddl VARCHAR2 (32767);
BEGIN
l_ddl := REPLACE (
REPLACE (
DBMS_LOB.SUBSTR (DBMS_METADATA.get_ddl ('TABLE', 'ACTIVITY_LOG', 'OLDSCHEMA'))
, q'["OLDSCHEMA"]'
, q'["NEWSCHEMA"]'
)
, q'["OLDTABLSPACE"]'
, q'["NEWTABLESPACE"]'
);
EXECUTE IMMEDIATE l_ddl;
END;
Simply write a query like:
create table new_table as select * from old_table where 1=2;
where new_table is the name of the new table that you want to create and old_table is the name of the existing table whose structure you want to copy, this will copy only structure.
SELECT * INTO newtable
FROM oldtable
WHERE 1 = 0;
Create a new, empty table using the schema of another. Just add a WHERE clause that causes the query to return no data:
WHERE 1 = 0 or similar false conditions work, but I dislike how they look. Marginally cleaner code for Oracle 12c+ IMHO is
CREATE TABLE bar AS
SELECT *
FROM foo
FETCH FIRST 0 ROWS ONLY;
Same limitations apply: only column definitions and their nullability are copied into a new table.
If one needs to create a table (with an empty structure) just to EXCHANGE PARTITION, it is best to use the "..FOR EXCHANGE.." clause. It's available only from Oracle version 12.2 onwards though.
CREATE TABLE t1_temp FOR EXCHANGE WITH TABLE t1;
This addresses 'ORA-14097' during the 'exchange partition' seamlessly if table structures are not exactly copied by normal CTAS operation. I have seen Oracle missing some of the "DEFAULT" column and "HIDDEN" columns definitions from the original table.
ORA-14097: column type or size mismatch in ALTER TABLE EXCHANGE
PARTITION
See this for further read...
you can also do a
create table abc_new as select * from abc;
then truncate the table abc_new. Hope this will suffice your requirement.
Using pl/sql developer you can right click on the table_name either in the sql workspace or in the object explorer, than click on "view" and than click "view sql" which generates the sql script to create the table along with all the constraints, indexes, partitions etc..
Next you run the script using the new_table_name
copy without table data
create table <target_table> as select * from <source_table> where 1=2;
copy with table data
create table <target_table> as select * from <source_table>;
In other way you can get ddl of table creation from command listed below, and execute the creation.
SELECT DBMS_METADATA.GET_DDL('TYPE','OBJECT_NAME','DATA_BASE_USER') TEXT FROM DUAL
TYPE is TABLE,PROCEDURE etc.
With this command you can get majority of ddl from database objects.
Create table target_table
As
Select *
from source_table
where 1=2;
Source_table is the table u wanna copy the structure of.
create table xyz_new as select * from xyz;
-- This will create table and copy all data.
delete from xyz_new;
-- This will have same table structure but all data copied will be deleted.
If you want to overcome the limitations specified by answer:
How can I create a copy of an Oracle table without copying the data?
The task above can be completed in two simple steps.
STEP 1:
CREATE table new_table_name AS(Select * from old_table_name);
The query above creates a duplicate of a table (with contents as well).
To get the structure, delete the contents of the table using.
STEP 2:
DELETE * FROM new_table_name.
Hope this solves your problem. And thanks to the earlier posts. Gave me a lot of insight.