SQL Antipatterns, Volume 1

Antipattern: Create Multiple Columns

You still have to account for multiple values in the attribute, but the new solution must store only a single value in each column. It might seem natural to create multiple columns in this table, each containing a single tag.

Multi-Column/anti/create-table.sql

​CREATE​ ​TABLE​ Bugs (
  bug_id      ​SERIAL​ ​PRIMARY​ ​KEY​,
  description ​VARCHAR​(1000),
  tag1        ​VARCHAR​(20),
  tag2        ​VARCHAR​(20),
  tag3        ​VARCHAR​(20)
);

As you assign tags to a given bug, you’d put values in one of these three columns. Unused columns remain null.

Multi-Column/anti/update.sql

​UPDATE​ Bugs ​SET​ tag2 = ​'performance'​ ​WHERE​ bug_id = 3456;

bug_id