primary key - MySQL update an AUTO_INCREMENT pk to preserve row ordering -


i have table 3 columns: id, foreign_id, , tag. queries on table ordered first foreign_id, tag, want deprecate tag column in favor of more reliable , auto-generated id. in doing so, need preserve ordering data stored in tag column without keeping tag around. ordering makes sense within scope of foreign_id column.

to solve problem, we've decided update ids within scope of each foreign_id such order of ids preserves tag order information.

how 1 update auto_increment primary key column such gets assigned next value in counter without changing rest of row?

alternatively, how 1 copy entire row (minus pk) new row , delete old row?

select max(id) @maxid the_table; update the_table set id = id + @maxid; set @i := 0; update the_table set id = (@i := @i + 1) order foreign_id, tag;

i not 100% positive work; don't kind of things update statements. alternatively, replace last update with:

insert the_table(id, foreign_id, tag)  select (@i := @i + 1) `new_id`, foreign_id, tag  the_table  order foreign_id, tag ; delete the_table  id >= @maxid ;

in either case, assumes current id values >= 0.


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