Question

Table Rule:

RuleID    RuleName
1         Rule1
2         Rule2
3         Rule3
4         Rule4

Table Equipment:

EquipmentID     EquipmentName     EquipmentCode
1               Equip1            E1
2               Equip2            E2
3               Equip3            E3

Table RuleEquipment:

EquipmentRuleID   RuleID    EquipmentID
1                 1         1
2                 1         2
3                 2         1
4                 2         3
5                 3         2

A user will query using one and only one EquipmentCode. I want to return the Rules which either have no associated Equipment or have the matching equipment.

So, if a user queries for E1, the result set should be

RuleID    RuleName
1         Rule1
2         Rule2
4         Rule4

I cannot put my finger on the WHERE clause for this. Any suggestions?

Answer 1

SELECT * FROM Rule 
WHERE Rule.ID NOT IN (SELECT RuleID FROM RuleEquipment)
OR Rule.ID IN 
(
   SELECT RuleID 
   FROM RuleEquipment 
      INNER JOIN Equipment ON RuleEquipment.EquipmentID = Equipment.EquipmentID
   WHERE Equipment.EquipmentCode = @inputEquipmentCode
)