CODEWITHSUNDEEP
mysql
jds
jds

Reputation: 8259

MySQL - Merge rows in table based on multiple criteria

I'd like to merge rows based on multiple criteria, essentially removing duplicates where I get to define what "duplicate" means. Here is an example table:

     ╔═════╦═══════╦═════╦═══════╗
     ║ id* ║ name  ║ age ║ grade ║
     ╠═════╬═══════╬═════╬═══════╣
     ║  1  ║ John  ║ 11  ║   5   ║
     ║  2  ║ John  ║ 11  ║   5   ║
     ║  3  ║ John  ║ 11  ║   6   ║
     ║  4  ║ Sam   ║ 14  ║   7   ║
     ║  5  ║ Sam   ║ 14  ║   7   ║
     ╚═════╩═══════╩═════╩═══════╝

In my example, let's say I want to merge on name and age but ignore grade. The result should be:

     ╔═════╦═══════╦═════╦═══════╗
     ║ id* ║ name  ║ age ║ grade ║
     ╠═════╬═══════╬═════╬═══════╣
     ║  1  ║ John  ║ 11  ║   5   ║
     ║  3  ║ John  ║ 11  ║   6   ║
     ║  4  ║ Sam   ║ 14  ║   7   ║
     ╚═════╩═══════╩═════╩═══════╝

I don't particularly care if the id column is updated to be incremental, but I suppose that would be nice.

Can I do this in MySQL?

Upvotes: 1

Views: 119

Answers (2)

zedfoxus
zedfoxus

Reputation: 37039

You could just delete the duplicates in place like this:

delete test
from test 
inner join (
  select name, age, grade, min(id) as minid, count(*)
  from test
  group by name, age, grade
  having count(*) > 1
) main on test.id = main.minid;

Example: http://sqlfiddle.com/#!9/f1a38/1

Upvotes: 1

durbnpoisn
durbnpoisn

Reputation: 4669

My suggestion, based on my above comment.

SELECT distinct name, age, grade 
into tempTable
from theTable

This will ignore the IDs and give you only a distinct dump, and into a new table.

Then you can either drop the old and, and rename the new one. Or truncate the old one, and dump this back in.

Upvotes: 1

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