TSQLServer - connects the queries to a MS SQL Server. Methods for commit control.
TSQLQuery - A query component that executes passthru SQL-statements. It can also cache all records in the record set and drop the server connection thus making it an ideal solution for applications with a large number of clients. The dataset is read-only and updates are performed thru the TSQLUpdate component.
TSQLUpdate - Updates tables on the server. The updates are triggered on every post event on the corresponding TSQLQuery component.
Some of our largest customers have used SQLQuery when building large scale web applications. We have done it here also in some customer projects. The reason our customers choose SQLQuery was that there are some memory leak problems with BDE, requiring them to restart the server at regular intervals. This problems hasn't been reported with SQLQuery.
Although I generally prefer middleware-based solutions, in testing TSQLQuery has been very fast and easy to work with. It presents a very light deployment burden (a few DLLs), and the developers are very eager to fix any bugs as soon as they are reported. If your application will only need to work with MS SQL Server, try this product!