How to copy a table schema with sql based on existance of the table? - sql

I want to duplicate a table schema, but only if the target table does not yet exist:
CREATE TABLE IF NOT EXISTS my_table_secondary as select * from my_table_primary
Problem: running this if the my_secondary_table exists results in:
ERROR: Syntaxerror at "as".
What could I do to make this sql statement work?
(postgres 9.4)

To duplicate the schema of a table, you need a completely different syntax.
create table if not exists my_table_secondary (
like my_table_primary including all
);
INCLUDING ALL is an abbreviated form of INCLUDING DEFAULTS INCLUDING
CONSTRAINTS INCLUDING INDEXES INCLUDING STORAGE INCLUDING COMMENTS.
It doesn't duplicate foreign key constraints. See CREATE TABLE. Search for "The LIKE clause".

Try this approach:
CREATE OR REPLACE VIEW my_view AS SELECT * FROM my_table_primary;
CREATE TABLE IF NOT EXISTS my_table_secondary LIKE my_view;
INSERT INTO my_table_secondary
SELECT * FROM my_view
WHERE NOT EXISTS ( SELECT * FROM my_table_secondary );
More on CREATE TABLE ... LIKE: http://www.postgresql.org/docs/9.1/static/sql-createtable.html

Related

I am not able to create temporary table in Bigquery

got below error while trying to create temporary table in Bigquery .
create or replace temporary table mss.Business.test2 as
select * from mss.Business.registration
Query error: Temporary tables may not be qualified at [2:36]
As mentioned by #Jaytiger names are not included in the CREATE TEMP TABLE statement.
You can create temporary table to store the results of a query as follows:
CREATE OR REPLACE TEMP TABLE <table1> as (SELECT * FROM `<dataset>.<table2>`);
SELECT * from <table1>
You can follow this documentation for further examples on Temp tables.

"create table new_table as select * from old_table" will give the table structure as old_table to new_table?

I have a table old_table (In oracle 10g)
I have to copy entire data of old_table into new_table.
At that moment, I will use
create table new_table
as
select * from old_table
Will this command create a table exactly like old_table?
For example, if old_table have some indexes on some columns.
If I use the above command, then, the new_table also have same indexes?
It will only create table with default settings and same structure (same columns and column types) as original table. It will not create any indexes, constraints, grants, triggers and any other objects dependent on the original table.
You can try this
create table new_table as select * from old_table
where 1=2;
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.)
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;

creating table as select is dropping the not null constraints in postgresql

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.

How can I create a table as a select from another database in Oracle?

Is it possible to create a table (in my dev db) using a SELECT from a different database?
I want something like:
create tmp_table as select * from prod_db.prod_schema.table
Is there syntax to do this, or do I need to create a database link first?
You have to create a datalink first.
Oracle cannot query other databases unless a DB link is created. If a DB link exists, as you remarked, you have to do :
create tmp_table as select * from prod_schema.table#prod_db
#Steve is correct that there has to be a DB Link, but the syntax is:
create tmp_table as select * from table#dblink
Don't forget to create your indexes. You can get this for all the tables in your schema with a query like this:
SELECT DBMS_METADATA.GET_DDL('INDEX',u.index_name)
FROM USER_INDEXES u;
CREATE TABLE table_name
AS SELECT * FROM schema_name.table_name;

How can I create a copy of an Oracle table without copying the data?

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.