cardinality

So, I've read a whole lot of answers here on stackoverflow, but I'm still confused about the whole concept thereof. Specifically, I've gone over this article (including all the ones it references), but can't seem to find a solid grasp on the concept (or perhaps it is my confusion between cardinality (n:m, etc.) and identities): Still Confused About Identifying vs. Non-Identifying Relationships My issue is this: I know that identifying relationships imply that the primary key of a child entity must include its foreign key, and that the opposite is true for non-identifying relationships (Is this

I'm quite new to relational databases and have been having a lot of trouble recently trying to understand an entity relationship diagram I've been given. Here it is: Solicitor ERD (ERD is for a made up solicitor company) Basically my task is to take this ERD and write an SQL script to create the database, obviously filling in the tables with data I can make up. The SQL syntax isn't the thing I'm having a hard time with, it's simply understanding the cardinality in the diagram. To me the terms '1 to 1', '1 to many', 'many to many' just don't click, I have no idea what they mean and how they

I have added a FULLTEXT index to one of my MySQL database tables as follows: ALTER TABLE members ADD FULLTEXT(about,fname,lname,job_title); The problem is that using phpmyadmin I can see the cardinality of my new index is only 1 . Does this mean the index will never be used? I have run a analyze table command but it didn't seem to do anything. analyze table members The respective types of the index fields are varchar(100), varchar(100), text, varchar(200) and the engine used is MyISAM and the table has about 30,000 rows, all unique. My MySQL version is 5.0.45. Am I doing something wrong?

Say you have a MySQL 5.0 MyISAM table with 100 million rows, with one index (other than primary key) on two integer columns. From my admittedly poor understanding of B-tree structure, I believe that a lower cardinality means the storage efficiency of the index is better, because there are less parent nodes. Whereas a higher cardinality means less efficient storage, but faster read performance, because it has to navigate through less branches to get to whatever data it is looking for to narrow down the rows for the query. (Note - by "low" vs "high", I don't mean e.g. 1 million vs 99 million for

I'm mainly an Actionscript developer and by no means an expert in SQL, but from time to time I have to develop simple server side stuff. So, I thought I'd ask more experienced people about the question in the title. My understanding is that you don't gain much by setting an index in a column that will hold few distinct values. I have a column that holds a boolean value (actually it's a small int, but I'm using it as a flag), and this column is used in the WHERE clauses of most of the queries I have. In a theoretical "average" case, half of the records' values will be 1 and the other half, 0.