MySQL Update old data after adding new column
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create a TEMPORARY MyISAM table with a 2-column PK, second column being AUTO_INCREMENT
INSERT INTO myisam_table (business_id, id) SELECT business_id, id ORDER BY business_id, id -- to get it to fill in review_number.
Do a multi-table UPDATE ... SET your_table.review_number = myisam_table.review_number between the two tables to copy those ids.