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
Previous
Next

Sub query in SQL Server

In SQL Server, a subquery is a query that is nested within another query. It allows you to retrieve data from one or more tables based on the results of an inner query. Subqueries can be used in various parts of a SQL statement, such as the SELECT, FROM, WHERE, and HAVING clauses.

Here's an example to illustrate the usage of a subquery in SQL Server:

Let's assume we have two tables: "Orders" and "Customers". The "Orders" table contains order information, including the customer ID, and the "Customers" table contains customer details, including the customer ID and country.

To find all orders placed by customers from a specific country, you can use a subquery within the WHERE clause. Here's the SQL query:


SELECT OrderID, OrderDate, CustomerID
FROM Orders
WHERE CustomerID IN (SELECT CustomerID FROM Customers WHERE Country = 'USA');

In this example, the subquery (SELECT CustomerID FROM Customers WHERE Country = 'USA') is used to retrieve all the customer IDs from the "Customers" table who belong to the country 'USA'. The outer query then uses this result to filter the orders placed by those customers.

Subqueries can also be used in other scenarios, such as in the SELECT clause to calculate aggregate values or in the FROM clause to create a derived table. The specific usage and syntax of subqueries may vary depending on the context in which they are used.

Previous
Next