What principles should be considered when creating non-clustered indexes in an SQL database?

When creating non-clustered indexes in SQL, the following principles are important:

• Column selection: Index columns that are frequently used in WHERE conditions, JOINs, or ORDER BY clauses.
• Cardinality: It is preferable to index columns with high uniqueness of values.
• Index size: Avoid indexing large text or binary fields, as this increases the index size and slows down operations.
• Number of indexes: Too many indexes slow down insert, update, and delete operations, so balance the number.
• Column order: In composite indexes, the order of columns is important and should match typical queries.

Example of creating a non-clustered index:

CREATE NONCLUSTERED INDEX IX_Users_LastName
ON Users (LastName);