SQL Server : insert missing rows - sql-server

Question

Using code sample below, how can I add missing Param for every EntityId without using WHILE? In the end, I want for every EntityId a row for Param 1, Param 2 and Param 3. I'm using SQL Server 2012.
DECLARE #Data TABLE
(
ID INT IDENTITY(1,1),
EntityId INT,
[Param] VARCHAR(25),
[Value] VARCHAR(25)
)
DECLARE #Param TABLE
(
[Param] VARCHAR(25)
)
INSERT INTO #Param([Param]) VALUES ('Param 1')
INSERT INTO #Param([Param]) VALUES ('Param 2')
INSERT INTO #Param([Param]) VALUES ('Param 3')
INSERT INTO #Data (EntityId, [Param], [Value]) VALUES(1, 'Param 1', 'Value 1')
INSERT INTO #Data (EntityId, [Param], [Value]) VALUES(1, 'Param 2', 'Value 2')
INSERT INTO #Data (EntityId, [Param], [Value]) VALUES(1, 'Param 3', 'Value 3')
INSERT INTO #Data (EntityId, [Param], [Value]) VALUES(2, 'Param 1', 'Value 1')
INSERT INTO #Data (EntityId, [Param], [Value]) VALUES(2, 'Param 3', 'Value 3')
INSERT INTO #Data (EntityId, [Param], [Value]) VALUES(3, 'Param 1', 'Value 1')
INSERT INTO #Data (EntityId, [Param], [Value]) VALUES(3, 'Param 3', 'Value 3')
INSERT INTO #Data (EntityId, [Param], [Value]) VALUES(4, 'Param 1', 'Value 1')

Answer 1

With a CROSS JOIN of #Param and the distinct EntityIds of #Data and a LEFT JOIN to #Data:
INSERT INTO #Data (EntityId, [Param])
SELECT e.EntityId, p.[Param]
FROM #Param p
CROSS JOIN (SELECT DISTINCT EntityId FROM #Data) AS e
LEFT JOIN #Data d ON d.EntityId = e.EntityId AND d.[Param] = p.[Param]
WHERE d.EntityId IS NULL
See the demo.
I'm not sure if you want the column [Value] to be populated with values just like [Param].

Answer 2

Note my comments.
-- 1. SAMPLE DATA
DECLARE #Data TABLE
(
ID INT IDENTITY(1,1),
EntityId INT,
[Param] VARCHAR(25),
[Value] VARCHAR(25)
);
DECLARE #Param TABLE
(
[Param] VARCHAR(25)
);
INSERT INTO #Param([Param])
VALUES ('Param 1'),('Param 2'),('Param 3')
INSERT INTO #Data (EntityId, [Param], [Value])
VALUES(1, 'Param 1', 'Value 1'),(1, 'Param 2', 'Value 2'),(1, 'Param 3', 'Value 3'),
(2, 'Param 1', 'Value 1'),(2, 'Param 3', 'Value 3'),(3, 'Param 1', 'Value 1'),
(3, 'Param 3', 'Value 3'),(4, 'Param 1', 'Value 1');
-- 2. How to get ALL values
SELECT
dist.EntityId,
p.[Param],
[Value] = REPLACE(p.[Param], 'Param','Value')
FROM
(
SELECT DISTINCT d.EntityId
FROM #data AS d -- OR WHEREEVER I CAN GET A DISTINCT LIST OF EntityIDs
) AS dist(EntityId)
CROSS JOIN #param AS p;
-- 3. How to identify MISSING values
SELECT
dist.EntityId,
[Param] = CAST(p.[Param] AS varchar(25)),
[Value] = CAST(REPLACE(p.[Param], 'Param','Value') AS varchar(25))
FROM
(
SELECT DISTINCT d.EntityId
FROM #data AS d -- OR WHEREEVER I CAN GET A DISTINCT LIST OF EntityIDs
) AS dist(EntityId)
CROSS JOIN #param AS p
EXCEPT
SELECT d.EntityId, d.[param], d.[value]
FROM #data AS d;
-- 4. How to add missing values
INSERT #data
SELECT
dist.EntityId,
[Param] = CAST(p.[Param] AS varchar(25)),
[Value] = CAST(REPLACE(p.[Param], 'Param','Value') AS varchar(25))
FROM
(
SELECT DISTINCT d.EntityId
FROM #data AS d -- OR WHEREEVER I CAN GET A DISTINCT LIST OF EntityIDs
) AS dist(EntityId)
CROSS JOIN #param AS p
EXCEPT
SELECT d.EntityId, d.[param], d.[value]
FROM #data AS d;

Answer 3

If you want to choose the EntityId which records will be inserted so this could be it.
declare #eId int
set #eId = 4
insert into #Data (EntityId, [Param], [Value])
select #eId, [Param], 'Value ' + CAST(RIGHT([Param],1) AS varchar(1))
from #Param
where [Param] NOT IN (select [Param] from #Data where EntityId = #eId)