Easiest way to duplicate rows

Question

The closest I can find to what I want to do is How to duplicate related rows, but my inexperience gets me lost. Basically, I want to copy a number of records, change one column and insert them back into the same table (so its almost a duplicate of the original data).

Table menuship is a hash table for a food menu (each row in the table will identify a menu category (starter, main course, or dessert for example), and products (fish and chips).

Table structure:

CREATE TABLE `menuship3` (
  `id` int(10) NOT NULL AUTO_INCREMENT,
  `headhash` char(40) DEFAULT NULL,
  `menucardhash` char(40) DEFAULT NULL,
  `menucathash` char(40) DEFAULT NULL,
  `producthash` char(40) DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `headhash` (`headhash`)
) ENGINE=InnoDB AUTO_INCREMENT=52 DEFAULT CHARSET=utf8

In programming circles, I would say I want to "fork" my data...

If my table content was like so:

id	headhash	menucardhash	menucathash	producthash
1	aaa	aaa	aaa	aaa
2	aaa	aaa	aaa	bbb
3	aaa	aaa	aaa	ccc
4	aaa	aaa	bbb	ddd
5	aaa	aaa	ccc	eee
6	aaa	other	xyz	fgi
7	aaa	other	xyz	fgh

I want to duplicate all records with menucardhash aaa (rows 1-5), so I will end up with a table containing 12 records. The extra records will have new menucarhash qqq instead of menucardhash aaa.

id	headhash	menucardhash	menucathash	producthash
8	aaa	qqq	aaa	aaa
9	aaa	qqq	aaa	bbb
10	aaa	qqq	aaa	ccc
11	aaa	qqq	bbb	ddd
12	aaa	qqq	ccc	eee

The result in effect means I have records that have similarity, records 1-5 are similar to records 8-12 - the differences being the id and menucardhash columns.

I was just going to select the records within PHP, change menucathash and send them back to the db, but I wondered if there was an SQL query that could do this for me and thus reduce cpu cycle overhead.

Is this possible via one or two queries, or am I better off having PHP carry the weight?

Answer 1

This is a very simple INSERT .. SELECT query.

The id is not included in the column list as it has the AUTO_INCREMENT property and will get values automatically. You only need to replace 'aaa' with the menucardhash value that you want to duplicate from and 'qqq' with the new value:

INSERT INTO menuship3
    (headhash, menucardhash, menucathash, producthash)
SELECT 
    headhash, 'qqq', menucathash, producthash
FROM 
    menuship3
WHERE 
    menucardhash = 'aaa' ;