SQL Server BasicsWhat is SQL Server database?What is RDBMS?What is Normalization?Why we use Denormalization?What_is_SQL?What is PL/SQL?Difference between SQL and PL/SQLDatabase TableOne to One RelationshipOne to Many RelationshipMany to Many RelationshipMany to One RelationshipString Data TypesNumber Data TypesDate Data TypesOther Data TypesCreate DatabaseDrop DatabaseCreating and Managing Users in SQL ServerCreate TableAlter TableDrop TableConstraints in SQL serverPrimary KeyForeign KeyUnique KeyCandidate KeyComposite KeyDifference between primary key and candidate keyPrimary key and foreign key relationshipSurrogate KeyCascading Referential Integrity ConstraintsSelf Referential Integrity ConstraintsInsert into statementInsert multiple recordsUpdate statementDelete statementTruncate statementDifference between Delete and TruncateAlias in SQL ServerSelect statementSelect DistinctSelect TopSelect IntoNull Functions(ISNULL(),NULLIF(),COALESCE())Sub QueryIdentity ColumnSequence objectDifference between sequence and identity columnSQL Server ClausesWHERE ClauseOrder By ClauseTop N ClauseGroup By ClauseHaving ClauseDifference between Where and HavingSQL Server OperatorsArithmetic OperatorsComparison OperatorsLogical OperatorsBitwise OperatorsAny OperatorsAll OperatorsUnion OperatorsUnion All OperatorsDifference between Union and Union AllIntersect OperatorExcept OperatorDifference between Except and IntersectJoinsInner JoinLeft JoinRight JoinFull JoinSelf JoinCross JoinViewsWhat are views?Create views using SSMSIndexed ViewsComplex ViewsCheck Option in ViewCheck Encryption in ViewSchema Binding Option in ViewRead-only ViewsUpdatable ViewsAdvantages and disadvantages of viewsCreate multiple views on one tableCan we implement index on views?Can we Perform Insert, update, delete operation on views?Stored Procedure and FunctionsWhat are Stored Procedures?Why we use stored procedures?Passing parameters to Stored procedureUser-Defined FunctionsDifference between UDF and Stored procedurePre-Defined Functions@@Indentity and Scope_IndentityNULLIF, ISNULL and COALESCE

What is Primary Key in SQL server?

In SQL Server, a primary key is a column or a set of columns in a table that uniquely identifies each row. It is a constraint that ensures the uniqueness and integrity of data within the table.

Here are some key characteristics of a primary key in SQL Server:

  1. Uniqueness: A primary key constraint guarantees that each value in the primary key column(s) is unique. No two rows in the table can have the same values in the primary key column(s). This uniqueness allows for the identification and differentiation of individual rows.
  2. Non-nullability: By default, a primary key column cannot contain null values. It enforces that the primary key column(s) must have a valid value for each row. This ensures that the primary key can reliably identify and reference a specific record.
  3. Single or Composite Primary Key: A primary key can be a single column or a combination of multiple columns. In the case of a composite primary key, the uniqueness constraint applies to the combination of values in the specified columns. This allows for more complex and precise identification of rows.
  4. Table Identity: The primary key provides a unique identifier for each row in a table. It serves as an intrinsic attribute that distinguishes one record from another. This identity can be used to reference and access specific rows efficiently.
  5. Indexing: SQL Server automatically creates a clustered index on the primary key column(s) by default. This index organizes the data in the table based on the primary key, which improves query performance when searching, sorting, or joining data based on the primary key.
  6. Foreign Key References: Primary keys are often used as references in foreign key constraints to establish relationships between tables. The primary key column(s) in one table serve as the target for foreign key columns in other related tables. This allows for maintaining data integrity and enforcing referential constraints across tables.
Example:

CREATE TABLE Employees (
   EmployeeID INT PRIMARY KEY,
   FirstName VARCHAR(50),
   LastName VARCHAR(50),
   Email VARCHAR(100)
);

In this example, the "EmployeeID" column is defined as the primary key. It ensures that each value in the "EmployeeID" column is unique and not null. The primary key constraint guarantees the uniqueness and integrity of the employee records in the "Employees" table, allowing for efficient identification and referencing of individual employees.