Question

Hello I have tables sctucture with datas and 2 small questions.

CREATE TABLE [dbo].[Parent] (
    [id] [int] NOT NULL,
    [Name] [nvarchar](50) NOT NULL, 
 CONSTRAINT [PK_Parent] PRIMARY KEY CLUSTERED 
(
    [id] ASC
)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
) ON [PRIMARY]

GO

CREATE TABLE [dbo].[Child1] (
    [Child1Id] [int] NOT NULL,
    [ParentId] [int] NOT NULL,
    [SomeData] [int] NOT NULL,  
 CONSTRAINT [PK_Child1] PRIMARY KEY CLUSTERED 
(
    [Child1Id] ASC
)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
) ON [PRIMARY]

GO

CREATE TABLE [dbo].[Child2] (
    [Child2Id] [int] NOT NULL,
    [ParentId] [int] NOT NULL,
    [SomeData] [int] NOT NULL,  
 CONSTRAINT [PK_Child2] PRIMARY KEY CLUSTERED 
(
    [Child2Id] ASC
)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
) ON [PRIMARY]


INSERT INTO Parent VALUES(1,'Name 1')
INSERT INTO Parent VALUES(2,'Name 2')
INSERT INTO Parent VALUES(3,'Name 3')
INSERT INTO Parent VALUES(4,'Name 4')


INSERT INTO [Child1] VALUES(1,1,50)
INSERT INTO [Child1] VALUES(2,1,125)
INSERT INTO [Child1] VALUES(3,2,255)


INSERT INTO [Child2] VALUES(1,1,2)
INSERT INTO [Child2] VALUES(2,2,4)
INSERT INTO [Child2] VALUES(3,2,8)
INSERT INTO [Child2] VALUES(4,3,16)

1. How select all parets record with at least one child type in both tables.
   I did next query
   but I don’t know optimal way to show total count of this records

   SELECT p.Name, count(Child1) , count(Child2)

2. How select all parets records only that exist in both tables ?
   SELECT p.Name, count(Child1) , count(Child2)

Thanks in Advice.

Answer 1

Query 1:

--at least one child record in either Child1 or Child2
select distinct p.*
from parent p
left outer join child1 c1 on p.id = c1.ParentId
left outer join child2 c2 on p.id = c2.ParentId
where coalesce(c1.ParentId, c2.ParentId) is not null

Query 2:

--at least one child record in both Child1 and Child2
select distinct p.*
from parent p
inner join child1 c1 on p.id = c1.ParentId
inner join child2 c2 on p.id = c2.ParentId

Note: If you just want to show the count of parent records, change

select distinct p.*

to

select count(distinct p.id)

in either query.