Most efficient method for persisting complex types with variable schemas in SQL

Question

What I\'m doing

I am creating an SQL table that will provide the back-end storage mechanism for complex-typed objects. I am trying to determine how

Answer 1

In part, it will depend of your DB Engine. You're using SQL Server, don't you?

Answering your topics:

1 - Comparing the value of a text field versus of a varchar field: if you're comparing two db fields, varchar fields are smarter. Nvarchar(max) stores data in unicode with 2*l+2 bytes, where "l" is the lengh. For performance issues, you will need consider how much larger tables will be, for selecting the best way to index (or not) your table fields. See the topic.

2 - Sometimes nested queries are easily created and executed, also serving as a way to reduce query time. But, depending of the complexity, would be better to use different kind of joins. The best way is try to do in both ways. Execute two or more times each query, for the DB engine "compiles" a query on first executing, then the subsequent are quite faster. Measure the times for different parameters and choose the best option.

"Sometimes you can rewrite a subquery to use JOIN and achieve better performance. The advantage of creating a JOIN is that you can evaluate tables in a different order from that defined by the query. The advantage of using a subquery is that it is frequently not necessary to scan all rows from the subquery to evaluate the subquery expression. For example, an EXISTS subquery can return TRUE upon seeing the first qualifying row." - link

3- There's no much information in this question, but if you will get the xml document directly from the table, would be a good idea insted a view. Again, it will depends of the view and the document.

4- Other issues is about the total records expected for your table; the indexing of the columns, in wich you need to consider sorting, joining, filtering, PK's and FK's. Each situation could demmand different aproaches. My sugestion is to invest some time reading about your database engine and queries functioning and relating to your system.

I hope I've helped.