Simple Easy Learning: SQL

Wednesday, 21 December 2011

SQL - Clone Tables

There may be a situation when you need an exact copy of a table, and CREATE TABLE ... SELECT... doesn't suit your purposes because the copy must include the same indexes, default values, and so forth.
If you are using MySQL RDBMS, you can handle this situation by following steps.

Use SHOW CREATE TABLE command to get a CREATE TABLE statement that specifies the source table's structure, indexes and all.
Modify the statement to change the table name to that of the clone table and execute the statement. This way you will have exact clone table.
Optionally, If you need the table contents copied as well, issue an INSERT INTO ... SELECT statement, too.

Example:

Try out following example to create a clone table for TUTORIALS_TBL whose structure is as follows:

Step 1:

Get complete structure about table

SQL> SHOW CREATE TABLE TUTORIALS_TBL \G;
*************************** 1. row ***************************
       Table: TUTORIALS_TBL
Create Table: CREATE TABLE `TUTORIALS_TBL` (
  `tutorial_id` int(11) NOT NULL auto_increment,
  `tutorial_title` varchar(100) NOT NULL default '',
  `tutorial_author` varchar(40) NOT NULL default '',
  `submission_date` date default NULL,
  PRIMARY KEY  (`tutorial_id`),
  UNIQUE KEY `AUTHOR_INDEX` (`tutorial_author`)
) TYPE=MyISAM
1 row in set (0.00 sec)

Step 2:

Rename this table and create another table

SQL> CREATE TABLE `CLONE_TBL` (
  -> `tutorial_id` int(11) NOT NULL auto_increment,
  -> `tutorial_title` varchar(100) NOT NULL default '',
  -> `tutorial_author` varchar(40) NOT NULL default '',
  -> `submission_date` date default NULL,
  -> PRIMARY KEY  (`tutorial_id`),
  -> UNIQUE KEY `AUTHOR_INDEX` (`tutorial_author`)
-> ) TYPE=MyISAM;
Query OK, 0 rows affected (1.80 sec)

Step 3:

After executing step 2 you will a clone table in your database. If you want to copy data from old table then you can do it by using INSERT INTO... SELECT statement.

SQL> INSERT INTO CLONE_TBL (tutorial_id,
    ->                        tutorial_title,
    ->                        tutorial_author,
    ->                        submission_date)
    -> SELECT tutorial_id,tutorial_title,
    ->        tutorial_author,submission_date,
    -> FROM TUTORIALS_TBL;
Query OK, 3 rows affected (0.07 sec)
Records: 3  Duplicates: 0  Warnings: 0

Finally you will have exact clone table as you wanted to have.

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