As a SQL Server developer or administrator, it is important to have a solid understanding of various concepts and features of SQL Server. In this article, we will explore some key concepts such as indexes, cursors, linked servers, collation, and relationships.
Indexes
Indexes play a crucial role in optimizing query performance in SQL Server. There are two main types of indexes: clustered and non-clustered indexes.
A clustered index reorders the way records in a table are physically stored. It is important to note that a table can have only one clustered index. The leaf nodes of a clustered index contain the actual data pages.
On the other hand, a non-clustered index does not change the physical order of the rows on disk. The logical order of the index does not match the physical stored order of the rows. The leaf nodes of a non-clustered index contain index rows, not the actual data pages.
A table can have different index configurations, including:
- No indexes
- A clustered index
- A clustered index and many non-clustered indexes
- Many non-clustered indexes
Cursors
Cursors are database objects used by applications to manipulate data in a set on a row-by-row basis. Unlike typical SQL commands that operate on all the rows in a set at once, cursors allow for more granular control over data manipulation.
Working with a cursor involves several steps:
- Declare the cursor
- Open the cursor
- Fetch rows from the cursor
- Process fetched rows
- Close the cursor
- Deallocate the cursor
Linked Servers
Linked Servers is a concept in SQL Server that allows you to add other SQL Server instances to a group and query both databases using T-SQL statements. With linked servers, you can easily retrieve, join, and combine remote data with local data.
To add a new linked server, you can use stored procedures like sp_addlinkedserver and sp_addlinkedsrvlogin.
Collation
Collation refers to a set of rules that determine how data is sorted and compared in SQL Server. It defines the correct character sequence and provides options for case-sensitivity, accent marks, kana character types, and character width.
There are different types of collation sensitivity:
- Case sensitivity: A and a, B and b, etc.
- Accent sensitivity: a and á, o and ó, etc.
- Kana sensitivity: When Japanese kana characters Hiragana and Katakana are treated differently.
- Width sensitivity: When a single-byte character (half-width) and the same character represented as a double-byte character (full-width) are treated differently.
Relationships
When designing database tables, it is important to establish relationships between them. There are three main types of relationships:
- One-to-One: This relationship can be implemented as a single table or rarely as two tables with primary and foreign key relationships.
- One-to-Many: This relationship is implemented by splitting the data into two tables with primary key and foreign key relationships.
- Many-to-Many: This relationship is implemented using a junction table with the keys from both tables forming the composite primary key of the junction table.
Having a clear understanding of these concepts will greatly enhance your ability to work with SQL Server effectively.
Thank you for reading!