Comments on: When to use a relational database: ternary logic http://whathesaid.ca/2006/07/29/when-to-use-a-relational-database-ternary-logic/ Techie, Teachie, North of 60° Thu, 12 Jan 2012 19:31:07 +0000 hourly 1 http://wordpress.org/?v=3.3.1 By: Dave http://whathesaid.ca/2006/07/29/when-to-use-a-relational-database-ternary-logic/comment-page-1/#comment-4323 Dave Fri, 28 Mar 2008 01:56:56 +0000 http://whathesaid.ca/2006/07/29/when-to-use-a-relational-database-ternary-logic/#comment-4323 John, I wouldn't worry about space, since a text/blob or varchar column will only take up a small amount of overhead if left empty and you may not get any of that back for a NULL anyway. The separate table idea is probably the most space-efficient, although it allows an item to have multiple notes if you're not careful about the PK (but maybe that's not a problem anyway). As for allowing NULL values for your notes or comments, unless you can clearly define the difference between a NULL note and an empty note, and see that definition as useful, I'd go with NOT NULL. NULL has its place, but avoiding it should be your default option. John,

I wouldn’t worry about space, since a text/blob or varchar column will only take up a small amount of overhead if left empty and you may not get any of that back for a NULL anyway. The separate table idea is probably the most space-efficient, although it allows an item to have multiple notes if you’re not careful about the PK (but maybe that’s not a problem anyway).

As for allowing NULL values for your notes or comments, unless you can clearly define the difference between a NULL note and an empty note, and see that definition as useful, I’d go with NOT NULL. NULL has its place, but avoiding it should be your default option.

]]> By: John Marabeas http://whathesaid.ca/2006/07/29/when-to-use-a-relational-database-ternary-logic/comment-page-1/#comment-4288 John Marabeas Tue, 25 Mar 2008 03:49:10 +0000 http://whathesaid.ca/2006/07/29/when-to-use-a-relational-database-ternary-logic/#comment-4288 With all you said, would it be okay to include a "notes" field (tinyblob datatype, let's say) in, say, a members table even though not every member will have a note associated with him/her? That being the case, would I assign a "NULL" value to the field so as waste a minimum amount of storage space if the field is left blank for those members with no notes? (Or should a separate table me made (called "notes") such that it will only contain information if there are notes associated with those members who have them)? With all you said, would it be okay to include a “notes” field (tinyblob datatype, let’s say) in, say, a members table even though not every member will have a note associated with him/her? That being the case, would I assign a “NULL” value to the field so as waste a minimum amount of storage space if the field is left blank for those members with no notes? (Or should a separate table me made (called “notes”) such that it will only contain information if there are notes associated with those members who have them)?

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