Using a CURSOR is not normally the best way to process through a set of records. Yet when a seasoned programmer moves to writing TSQL for the first time they frequently look for ways to process a sets of records one row at a time. They do this because they are not used to thinking about processing records as a set. In order to process through a TSQL record set a row at a time you can use a cursor. A cursor is a record set that is defined with the DECLARE CURSOR statement. Cursors can be defined as either read-only or updatable. In this article I will introduce you to using cursors to do record level processing one row at a time.
When you build applications that store records in SQL Server you will most likely have to store date and time values as part of the data. To manage all the different date related tasks you might need to perform Microsoft has introduced a number of date functions. In this stairway I will be exploring those date and time functions.
In SQL Server there are 4 different ranking functions: RANK, DENSE_RANK, NTILE, and ROW_NUMBER. These ranking functions were introduced in SQL Server 2005. In this stairway level I will be reviewing each of these different ranking functions, and will show you how to use them by providing a few examples.
Joining tables is a crucial concept to understanding data relationships in a relational database. When you are working with your SQL Server data, you will often need to join tables to produce the results your application requires. Having a good understanding of set theory, and the mathematical operators available and how they are used to join tables will make it easier for you to retrieve the data you need from SQL Server.
A relational database contains tables that relate to each other by key values. When querying data from these related tables you may choose to select data from a single table or many tables. If you select data from many tables, you normally join those tables together using specified join criteria. The concepts of selecting data from tables and joining tables together is all about managing and manipulating sets of data. In Level 4 of this Stairway we will explore the concepts of set theory and mathematical operators to join, merge, and return data from multiple SQL Server tables.
This stairway level will expand on the subquery topic by discussing a type of subquery known as a correlated subquery, and explores what a correlated subquery is and how it is different from a normal subquery.