Question

In my case, every “item” either has a property , or not. The properties can be some hundreds, so I will need , say, max 1000 true/false bits per item.

Is there a way to store those bits in one field of the item ?

Answer 1

If you’re looking for a way to do this in a way that’s searchable, then no.

A couple searchable methods (involving more than 1 column and/or table):

• Use a bunch of SET columns. You’re limited to 64 items (on/offs) in a set, but you cna probably figure out a way to group them.
• Use 3 tables: Items (id, …), FlagNames(id, name), and a pivot table ItemFlags(item_id, flag_id). You can then query for items with joins.

If you don’t need it to be searchable, then all you need is a method to serialize your data before you put it in the database, and a unserialize it when you pull it out, then use a char, or varchar column.

• Use facilities built in to your language (PHP’s serialize/unserialize).
• Concatenate a series of “y” and “n” characters together.
• Bit-pack your values into a string (8 bits per character) in the client before making a call to the MySQL database, and unpack them when retrieving data out of the database. This is the most efficient storage mechanism (if all rows are the same, use char[x], not varchar[x]) at the expense of the data not being searchable and slightly more complicated code.