Class NotExists

Namespace

YndigoBlue.Velocity.Functions

Assembly

YndigoBlue.Velocity.dll

Represents the NOT EXISTS operator that tests whether a subquery returns no rows.

public class NotExists : Function, ICheckItem, IDefaultItem, IFilterItem, IElement

Inheritance

object

Function

NotExists

Implements

ICheckItem

IDefaultItem

IFilterItem

IElement

Remarks

The NOT EXISTS operator returns true if the subquery returns zero rows, and false if it returns one or more rows. Like EXISTS, it uses short-circuit evaluation for efficiency. This is useful for finding records without related data, implementing anti-joins, or filtering based on the absence of matching conditions. NOT EXISTS is often more readable and efficient than LEFT JOIN with NULL checks for finding unmatched records.

Examples

Find all orders that have not yet been shipped:

var schema = manager.LoadSchema("logistics");
var orders = schema["orders"];
var shipments = schema["shipments"];

var subQuery = new Query()
    .Select([ shipments["id"] ])
    .From(shipments)
    .Where(new Criterion<Column>(shipments["order_id"], ConditionalType.Equals, orders["id"]));

var query = new Query()
    .Select([ orders["id"], orders["status"] ])
    .From(orders)
    .Where(new Criterion<Expression>(new Expression(new NotExists(subQuery))));

var results = manager.Retrieve(query);

Constructors

NotExists(IEnumerable<IElement>)

Initializes a new instance of NOT EXISTS for multiple elements.

NotExists(IElement)

Initializes a new instance of NOT EXISTS for a single element.