Merge not working for insert a record when it's doesn't exist - sql

Can I use Merge to insert a record when it's doesn't exist like below,
MERGE INTO [dbo].[Test] AS [Target]
USING (SELECT DISTINCT [Name] FROM [dbo].[Test]) AS [Source]
ON [Target].[Name] = [Source].[Name]
WHEN NOT MATCHED THEN
INSERT ([Id], [Name])
VALUES (NEWID(), 'Hello');
If the record with value Hello does not exists in table Test, insert it otherwise don't do anything. With above code record is not inserted even I don't have this record in table. And there are no errors.
I know how to accomplish this using insert ... where not exists (...) but am specifically wanting to know how to do it using a merge statement.


The reason your merge statement wasn't working is that you were merging the same table, dbo.Test, back onto itself, so of course there is no missing record.
You can insert a single missing record as follows, where you create a source query to contain the record(s) you wish to insert:
declare #Test table (id uniqueidentifier, [Name] nvarchar(64))
select * from #Test
-- Returns
-- id | Name
-- ----------------------------------------------
MERGE INTO #Test AS [Target]
USING (select 'Hello' [Name]) AS [Source]
ON [Target].[Name] = [Source].[Name]
WHEN NOT MATCHED THEN
INSERT ([Id], [Name])
VALUES (NEWID(), [Name]);
select * from #Test
-- Returns
-- id | Name
-- ----------------------------------------------
-- C1C87CD5-F745-436D-BD8D-55B2AF431BED | Hello


I agree with the answer from Dale K. Its correct.
If I suppose you might have a source_table from where the data needs to get inserted and not to get inserted if the record already exists then you can do the following.
Instead of the MERGE you can
insert
into dbo.Test
(id
,name
)
select top 1
newID()
,'Hello'
from dbo.Test a
where not exists(select 1
from dbo.Test b
where b.name='Hello')

Related

SQL Server: return joined data from insert select

I perform steps:
Create temporal table and fill it with data and unique order column [_oid]
Insert everything from temporal table into real table except fictional [_oid], outputting generated [id]'s
Return those generated [id]'s along with corresponding [_oid]
SQL:
CREATE TABLE #temp
(
[Hash] INT NOT NULL,
[Size] INT NOT NULL,
[Data] NVARCHAR(MAX),
[_oid] INT NOT NULL
)
--here insert data into #temp--
INSERT [dbo].[TestObjects]
OUTPUT INSERTED.[Id]
SELECT [Hash], [Size], [Data]
FROM #temp
DROP TABLE #temp
How I can return ([Id], [_oid]) rows ? ....Or at least return [Id] ordered by [_oid] ?
I know insert does not preserve order of inserted items in it's output, but still...

I think you what you are asking for is INSERT INTO, as so:
INSERT INTO [dbo].[TestObjects]
SELECT Hash, Size, Data FROM #temp
ORDER BY _oid
But as you say, there's no guarantee about order when you select from TestObjects, so if it's important can you not have a field in TestObjects you can ORDER BY when you SELECT from it?

IF your insert into #temp is such that both o_id and (hash,size,data) are unique for each row (ie keys), then you could retrieve the inserted o_id from #temp:
select t.[_oid],to.[Id]
from #temp t
inner join [dbo].[TestObjects] to
on t.Hash=to.Hash and t.Size=to.Size and t.data=to.data

As noted by George Menoutis, I did merge:
MERGE [dbo].[TestObjects] AS T_Base
USING #temp AS T_Source
ON (0<>0)
WHEN NOT MATCHED THEN INSERT ([Hash],[Size],[Data]) VALUES (T_Source.[Hash],T_Source.[Size],T_Source.[Data])
OUTPUT INSERTED.[Id], T_Source.[_oid];
If anyone have better approach - feel free to contribute to this answer.

INSERT inside an INSERT statement and use its ID in the outer INSERT [duplicate]

Very simplified, I have two tables Source and Target.
declare #Source table (SourceID int identity(1,2), SourceName varchar(50))
declare #Target table (TargetID int identity(2,2), TargetName varchar(50))
insert into #Source values ('Row 1'), ('Row 2')
I would like to move all rows from #Source to #Target and know the TargetID for each SourceID because there are also the tables SourceChild and TargetChild that needs to be copied as well and I need to add the new TargetID into TargetChild.TargetID FK column.
There are a couple of solutions to this.
Use a while loop or cursors to insert one row (RBAR) to Target at a time and use scope_identity() to fill the FK of TargetChild.
Add a temp column to #Target and insert SourceID. You can then join that column to fetch the TargetID for the FK in TargetChild.
SET IDENTITY_INSERT OFF for #Target and handle assigning new values yourself. You get a range that you then use in TargetChild.TargetID.
I'm not all that fond of any of them. The one I used so far is cursors.
What I would really like to do is to use the output clause of the insert statement.
insert into #Target(TargetName)
output inserted.TargetID, S.SourceID
select SourceName
from #Source as S
But it is not possible
The multi-part identifier "S.SourceID" could not be bound.
But it is possible with a merge.
merge #Target as T
using #Source as S
on 0=1
when not matched then
insert (TargetName) values (SourceName)
output inserted.TargetID, S.SourceID;
Result
TargetID SourceID
----------- -----------
2 1
4 3
I want to know if you have used this? If you have any thoughts about the solution or see any problems with it? It works fine in simple scenarios but perhaps something ugly could happen when the query plan get really complicated due to a complicated source query. Worst scenario would be that the TargetID/SourceID pairs actually isn't a match.
MSDN has this to say about the from_table_name of the output clause.
Is a column prefix that specifies a table included in the FROM clause of a DELETE, UPDATE, or MERGE statement that is used to specify the rows to update or delete.
For some reason they don't say "rows to insert, update or delete" only "rows to update or delete".
Any thoughts are welcome and totally different solutions to the original problem is much appreciated.

In my opinion this is a great use of MERGE and output. I've used in several scenarios and haven't experienced any oddities to date.
For example, here is test setup that clones a Folder and all Files (identity) within it into a newly created Folder (guid).
DECLARE #FolderIndex TABLE (FolderId UNIQUEIDENTIFIER PRIMARY KEY, FolderName varchar(25));
INSERT INTO #FolderIndex
(FolderId, FolderName)
VALUES(newid(), 'OriginalFolder');
DECLARE #FileIndex TABLE (FileId int identity(1,1) PRIMARY KEY, FileName varchar(10));
INSERT INTO #FileIndex
(FileName)
VALUES('test.txt');
DECLARE #FileFolder TABLE (FolderId UNIQUEIDENTIFIER, FileId int, PRIMARY KEY(FolderId, FileId));
INSERT INTO #FileFolder
(FolderId, FileId)
SELECT FolderId,
FileId
FROM #FolderIndex
CROSS JOIN #FileIndex; -- just to illustrate
DECLARE #sFolder TABLE (FromFolderId UNIQUEIDENTIFIER, ToFolderId UNIQUEIDENTIFIER);
DECLARE #sFile TABLE (FromFileId int, ToFileId int);
-- copy Folder Structure
MERGE #FolderIndex fi
USING ( SELECT 1 [Dummy],
FolderId,
FolderName
FROM #FolderIndex [fi]
WHERE FolderName = 'OriginalFolder'
) d ON d.Dummy = 0
WHEN NOT MATCHED
THEN INSERT
(FolderId, FolderName)
VALUES (newid(), 'copy_'+FolderName)
OUTPUT d.FolderId,
INSERTED.FolderId
INTO #sFolder (FromFolderId, toFolderId);
-- copy File structure
MERGE #FileIndex fi
USING ( SELECT 1 [Dummy],
fi.FileId,
fi.[FileName]
FROM #FileIndex fi
INNER
JOIN #FileFolder fm ON
fi.FileId = fm.FileId
INNER
JOIN #FolderIndex fo ON
fm.FolderId = fo.FolderId
WHERE fo.FolderName = 'OriginalFolder'
) d ON d.Dummy = 0
WHEN NOT MATCHED
THEN INSERT ([FileName])
VALUES ([FileName])
OUTPUT d.FileId,
INSERTED.FileId
INTO #sFile (FromFileId, toFileId);
-- link new files to Folders
INSERT INTO #FileFolder (FileId, FolderId)
SELECT sfi.toFileId, sfo.toFolderId
FROM #FileFolder fm
INNER
JOIN #sFile sfi ON
fm.FileId = sfi.FromFileId
INNER
JOIN #sFolder sfo ON
fm.FolderId = sfo.FromFolderId
-- return
SELECT *
FROM #FileIndex fi
JOIN #FileFolder ff ON
fi.FileId = ff.FileId
JOIN #FolderIndex fo ON
ff.FolderId = fo.FolderId

I would like to add another example to add to #Nathan's example, as I found it somewhat confusing.
Mine uses real tables for the most part, and not temp tables.
I also got my inspiration from here: another example
-- Copy the FormSectionInstance
DECLARE #FormSectionInstanceTable TABLE(OldFormSectionInstanceId INT, NewFormSectionInstanceId INT)
;MERGE INTO [dbo].[FormSectionInstance]
USING
(
SELECT
fsi.FormSectionInstanceId [OldFormSectionInstanceId]
, #NewFormHeaderId [NewFormHeaderId]
, fsi.FormSectionId
, fsi.IsClone
, #UserId [NewCreatedByUserId]
, GETDATE() NewCreatedDate
, #UserId [NewUpdatedByUserId]
, GETDATE() NewUpdatedDate
FROM [dbo].[FormSectionInstance] fsi
WHERE fsi.[FormHeaderId] = #FormHeaderId
) tblSource ON 1=0 -- use always false condition
WHEN NOT MATCHED
THEN INSERT
( [FormHeaderId], FormSectionId, IsClone, CreatedByUserId, CreatedDate, UpdatedByUserId, UpdatedDate)
VALUES( [NewFormHeaderId], FormSectionId, IsClone, NewCreatedByUserId, NewCreatedDate, NewUpdatedByUserId, NewUpdatedDate)
OUTPUT tblSource.[OldFormSectionInstanceId], INSERTED.FormSectionInstanceId
INTO #FormSectionInstanceTable(OldFormSectionInstanceId, NewFormSectionInstanceId);
-- Copy the FormDetail
INSERT INTO [dbo].[FormDetail]
(FormHeaderId, FormFieldId, FormSectionInstanceId, IsOther, Value, CreatedByUserId, CreatedDate, UpdatedByUserId, UpdatedDate)
SELECT
#NewFormHeaderId, FormFieldId, fsit.NewFormSectionInstanceId, IsOther, Value, #UserId, CreatedDate, #UserId, UpdatedDate
FROM [dbo].[FormDetail] fd
INNER JOIN #FormSectionInstanceTable fsit ON fsit.OldFormSectionInstanceId = fd.FormSectionInstanceId
WHERE [FormHeaderId] = #FormHeaderId

Here's a solution that doesn't use MERGE (which I've had problems with many times I try to avoid if possible). It relies on two memory tables (you could use temp tables if you want) with IDENTITY columns that get matched, and importantly, using ORDER BY when doing the INSERT, and WHERE conditions that match between the two INSERTs... the first one holds the source IDs and the second one holds the target IDs.
-- Setup... We have a table that we need to know the old IDs and new IDs after copying.
-- We want to copy all of DocID=1
DECLARE #newDocID int = 99;
DECLARE #tbl table (RuleID int PRIMARY KEY NOT NULL IDENTITY(1, 1), DocID int, Val varchar(100));
INSERT INTO #tbl (DocID, Val) VALUES (1, 'RuleA-2'), (1, 'RuleA-1'), (2, 'RuleB-1'), (2, 'RuleB-2'), (3, 'RuleC-1'), (1, 'RuleA-3')
-- Create a break in IDENTITY values.. just to simulate more realistic data
INSERT INTO #tbl (Val) VALUES ('DeleteMe'), ('DeleteMe');
DELETE FROM #tbl WHERE Val = 'DeleteMe';
INSERT INTO #tbl (DocID, Val) VALUES (6, 'RuleE'), (7, 'RuleF');
SELECT * FROM #tbl t;
-- Declare TWO temp tables each with an IDENTITY - one will hold the RuleID of the items we are copying, other will hold the RuleID that we create
DECLARE #input table (RID int IDENTITY(1, 1), SourceRuleID int NOT NULL, Val varchar(100));
DECLARE #output table (RID int IDENTITY(1,1), TargetRuleID int NOT NULL, Val varchar(100));
-- Capture the IDs of the rows we will be copying by inserting them into the #input table
-- Important - we must specify the sort order - best thing is to use the IDENTITY of the source table (t.RuleID) that we are copying
INSERT INTO #input (SourceRuleID, Val) SELECT t.RuleID, t.Val FROM #tbl t WHERE t.DocID = 1 ORDER BY t.RuleID;
-- Copy the rows, and use the OUTPUT clause to capture the IDs of the inserted rows.
-- Important - we must use the same WHERE and ORDER BY clauses as above
INSERT INTO #tbl (DocID, Val)
OUTPUT Inserted.RuleID, Inserted.Val INTO #output(TargetRuleID, Val)
SELECT #newDocID, t.Val FROM #tbl t
WHERE t.DocID = 1
ORDER BY t.RuleID;
-- Now #input and #output should have the same # of rows, and the order of both inserts was the same, so the IDENTITY columns (RID) can be matched
-- Use this as the map from old-to-new when you are copying sub-table rows
-- Technically, #input and #output don't even need the 'Val' columns, just RID and RuleID - they were included here to prove that the rules matched
SELECT i.*, o.* FROM #output o
INNER JOIN #input i ON i.RID = o.RID
-- Confirm the matching worked
SELECT * FROM #tbl t

SSIS Staging Table to Normalized form

I could be down the wrong path with this. However, here goes. I am trying to take multiple excel sheets and load them into SQL Server using SSIS.
Excel sheet:
RQ|Descr|PartNum|Manufacturer|...
I am loading this into a staging table with a couple of derived columns:
RQ|Descr|PartNum|Manufacturer|Origin|DateTime|...
This is no big deal, I am able to do this easily. However, the problem is how to get the data from the staging table to the correct table and ensuring FK constraints are followed. See below for an illustration.
My goal is to take RQ|Descr|PartNum|Manufacturer|Origin|DateTime|...
and populate multiple tables
[t1] id|RQ|Descr|Origin|DateTime
[t2] id|t1_id|PartNum|Manufacturer
[t3] id|t1_id|...
I have tried MERGE however I am unsure how to keep the FK relationship.
MERGE INTO spin_item AS targ
USING ssis_stage AS src ON 1=0 -- always generates "not matched by target"
WHEN NOT MATCHED BY TARGET THEN
-- INSERT into spin_item:
INSERT (description, reqqty, price, origin, datetime, exclude, status, siteid, production, repairable)
VALUES (src.description, src.rq, src.price, src.origin, GETDATE(), 0, 'N', '', 0, 0)
-- INSERT into spin_part:
OUTPUT inserted.ID, src.manufacturer, src.partnum
INTO spin_part (ID, src.manufacturer, src.partnum);
I have looked into this SSIS : Using multicast to enter data into 2 RELATED destinations but this is for a one-to-many relationship. So, I am not sure how to populate my t1 table and use the id to populate t2, t3 from the staging table.
EDIT: Below, seems to be a working solution. However, I am not sure that it is a good solution.
BEGIN
SET IDENTITY_INSERT dbo.spin_item ON
--Insert into spin_item
MERGE INTO spin_item AS targ
USING ssis_stage AS src ON 1=0
WHEN NOT MATCHED BY TARGET THEN
INSERT (id, description, reqqty, price, origin, datetime, exclude, status, siteid, production, repairable)
VALUES (src.id, src.description, src.rq, src.price, src.origin, GETDATE(), 0, 'N', '', 0, 0);
SET IDENTITY_INSERT dbo.spin_item OFF
--Insert into spin_part
MERGE INTO spin_part AS targ
USING ssis_stage AS src ON 1=0
WHEN NOT MATCHED BY TARGET AND src.partnum IS NOT NULL THEN
INSERT (itemid_id, manufacturer, partnum, catalognum, [primary])
VALUES (src.id, src.manufacturer, src.partnum, src.partnum, 1);
--Insert into spin_stock
MERGE INTO spin_stock AS targ
USING ssis_stage AS src ON 1=0
WHEN NOT MATCHED BY TARGET AND src.stock IS NOT NULL THEN
INSERT (itemid_id, stocknum)
VALUES (src.id, src.stock);
--Insert into spin_collaboration
MERGE INTO spin_collaboration AS targ
USING ssis_stage AS src ON 1=0
WHEN NOT MATCHED BY TARGET AND src.notes IS NOT NULL THEN
INSERT (itemid_id, comment, datetime)
VALUES (src.id, src.notes, GETDATE());
DELETE FROM ssis_stage WHERE id > 0 --Instead of Truncate since auto_increment will reset.
END

You can create an ID column on your staging table, based off your target tables that is then used as the FK in each table insert:
declare #source table (ID int, a int, b int, c int);
insert into #source values
(null,1,1,1)
,(null,1,1,2)
,(null,1,2,2)
,(null,5,3,2)
,(null,7,1,2)
,(null,2,1,2)
declare #target1 table (ID int, a int);
insert into #target1 values
(1,5)
,(2,6)
,(3,99);
declare #target2 table (ID int, b int, c int);
insert into #target2 values
(1,3,2)
,(2,9,7)
,(3,57,3);
update s
set ID = ss.IDNew
from #source s
inner join (
select row_number() over (order by a,b,c) + (select max(ID) from #target1) as IDNew
,a
,b
,c
from #source
) ss
on(s.a = ss.a
and s.b = ss.b
and s.c = ss.c
);
select * from #target1;
select * from #source;
insert into #target1
select ID
,a
from #source;
insert into #target2
select ID
,b
,c
from #source;
select * from #target1;
select * from #target2;

SQL Server, Select/Output/Insert - need to select value for output but not insert [duplicate]

Very simplified, I have two tables Source and Target.
declare #Source table (SourceID int identity(1,2), SourceName varchar(50))
declare #Target table (TargetID int identity(2,2), TargetName varchar(50))
insert into #Source values ('Row 1'), ('Row 2')
I would like to move all rows from #Source to #Target and know the TargetID for each SourceID because there are also the tables SourceChild and TargetChild that needs to be copied as well and I need to add the new TargetID into TargetChild.TargetID FK column.
There are a couple of solutions to this.
Use a while loop or cursors to insert one row (RBAR) to Target at a time and use scope_identity() to fill the FK of TargetChild.
Add a temp column to #Target and insert SourceID. You can then join that column to fetch the TargetID for the FK in TargetChild.
SET IDENTITY_INSERT OFF for #Target and handle assigning new values yourself. You get a range that you then use in TargetChild.TargetID.
I'm not all that fond of any of them. The one I used so far is cursors.
What I would really like to do is to use the output clause of the insert statement.
insert into #Target(TargetName)
output inserted.TargetID, S.SourceID
select SourceName
from #Source as S
But it is not possible
The multi-part identifier "S.SourceID" could not be bound.
But it is possible with a merge.
merge #Target as T
using #Source as S
on 0=1
when not matched then
insert (TargetName) values (SourceName)
output inserted.TargetID, S.SourceID;
Result
TargetID SourceID
----------- -----------
2 1
4 3
I want to know if you have used this? If you have any thoughts about the solution or see any problems with it? It works fine in simple scenarios but perhaps something ugly could happen when the query plan get really complicated due to a complicated source query. Worst scenario would be that the TargetID/SourceID pairs actually isn't a match.
MSDN has this to say about the from_table_name of the output clause.
Is a column prefix that specifies a table included in the FROM clause of a DELETE, UPDATE, or MERGE statement that is used to specify the rows to update or delete.
For some reason they don't say "rows to insert, update or delete" only "rows to update or delete".
Any thoughts are welcome and totally different solutions to the original problem is much appreciated.

In my opinion this is a great use of MERGE and output. I've used in several scenarios and haven't experienced any oddities to date.
For example, here is test setup that clones a Folder and all Files (identity) within it into a newly created Folder (guid).
DECLARE #FolderIndex TABLE (FolderId UNIQUEIDENTIFIER PRIMARY KEY, FolderName varchar(25));
INSERT INTO #FolderIndex
(FolderId, FolderName)
VALUES(newid(), 'OriginalFolder');
DECLARE #FileIndex TABLE (FileId int identity(1,1) PRIMARY KEY, FileName varchar(10));
INSERT INTO #FileIndex
(FileName)
VALUES('test.txt');
DECLARE #FileFolder TABLE (FolderId UNIQUEIDENTIFIER, FileId int, PRIMARY KEY(FolderId, FileId));
INSERT INTO #FileFolder
(FolderId, FileId)
SELECT FolderId,
FileId
FROM #FolderIndex
CROSS JOIN #FileIndex; -- just to illustrate
DECLARE #sFolder TABLE (FromFolderId UNIQUEIDENTIFIER, ToFolderId UNIQUEIDENTIFIER);
DECLARE #sFile TABLE (FromFileId int, ToFileId int);
-- copy Folder Structure
MERGE #FolderIndex fi
USING ( SELECT 1 [Dummy],
FolderId,
FolderName
FROM #FolderIndex [fi]
WHERE FolderName = 'OriginalFolder'
) d ON d.Dummy = 0
WHEN NOT MATCHED
THEN INSERT
(FolderId, FolderName)
VALUES (newid(), 'copy_'+FolderName)
OUTPUT d.FolderId,
INSERTED.FolderId
INTO #sFolder (FromFolderId, toFolderId);
-- copy File structure
MERGE #FileIndex fi
USING ( SELECT 1 [Dummy],
fi.FileId,
fi.[FileName]
FROM #FileIndex fi
INNER
JOIN #FileFolder fm ON
fi.FileId = fm.FileId
INNER
JOIN #FolderIndex fo ON
fm.FolderId = fo.FolderId
WHERE fo.FolderName = 'OriginalFolder'
) d ON d.Dummy = 0
WHEN NOT MATCHED
THEN INSERT ([FileName])
VALUES ([FileName])
OUTPUT d.FileId,
INSERTED.FileId
INTO #sFile (FromFileId, toFileId);
-- link new files to Folders
INSERT INTO #FileFolder (FileId, FolderId)
SELECT sfi.toFileId, sfo.toFolderId
FROM #FileFolder fm
INNER
JOIN #sFile sfi ON
fm.FileId = sfi.FromFileId
INNER
JOIN #sFolder sfo ON
fm.FolderId = sfo.FromFolderId
-- return
SELECT *
FROM #FileIndex fi
JOIN #FileFolder ff ON
fi.FileId = ff.FileId
JOIN #FolderIndex fo ON
ff.FolderId = fo.FolderId

I would like to add another example to add to #Nathan's example, as I found it somewhat confusing.
Mine uses real tables for the most part, and not temp tables.
I also got my inspiration from here: another example
-- Copy the FormSectionInstance
DECLARE #FormSectionInstanceTable TABLE(OldFormSectionInstanceId INT, NewFormSectionInstanceId INT)
;MERGE INTO [dbo].[FormSectionInstance]
USING
(
SELECT
fsi.FormSectionInstanceId [OldFormSectionInstanceId]
, #NewFormHeaderId [NewFormHeaderId]
, fsi.FormSectionId
, fsi.IsClone
, #UserId [NewCreatedByUserId]
, GETDATE() NewCreatedDate
, #UserId [NewUpdatedByUserId]
, GETDATE() NewUpdatedDate
FROM [dbo].[FormSectionInstance] fsi
WHERE fsi.[FormHeaderId] = #FormHeaderId
) tblSource ON 1=0 -- use always false condition
WHEN NOT MATCHED
THEN INSERT
( [FormHeaderId], FormSectionId, IsClone, CreatedByUserId, CreatedDate, UpdatedByUserId, UpdatedDate)
VALUES( [NewFormHeaderId], FormSectionId, IsClone, NewCreatedByUserId, NewCreatedDate, NewUpdatedByUserId, NewUpdatedDate)
OUTPUT tblSource.[OldFormSectionInstanceId], INSERTED.FormSectionInstanceId
INTO #FormSectionInstanceTable(OldFormSectionInstanceId, NewFormSectionInstanceId);
-- Copy the FormDetail
INSERT INTO [dbo].[FormDetail]
(FormHeaderId, FormFieldId, FormSectionInstanceId, IsOther, Value, CreatedByUserId, CreatedDate, UpdatedByUserId, UpdatedDate)
SELECT
#NewFormHeaderId, FormFieldId, fsit.NewFormSectionInstanceId, IsOther, Value, #UserId, CreatedDate, #UserId, UpdatedDate
FROM [dbo].[FormDetail] fd
INNER JOIN #FormSectionInstanceTable fsit ON fsit.OldFormSectionInstanceId = fd.FormSectionInstanceId
WHERE [FormHeaderId] = #FormHeaderId

Here's a solution that doesn't use MERGE (which I've had problems with many times I try to avoid if possible). It relies on two memory tables (you could use temp tables if you want) with IDENTITY columns that get matched, and importantly, using ORDER BY when doing the INSERT, and WHERE conditions that match between the two INSERTs... the first one holds the source IDs and the second one holds the target IDs.
-- Setup... We have a table that we need to know the old IDs and new IDs after copying.
-- We want to copy all of DocID=1
DECLARE #newDocID int = 99;
DECLARE #tbl table (RuleID int PRIMARY KEY NOT NULL IDENTITY(1, 1), DocID int, Val varchar(100));
INSERT INTO #tbl (DocID, Val) VALUES (1, 'RuleA-2'), (1, 'RuleA-1'), (2, 'RuleB-1'), (2, 'RuleB-2'), (3, 'RuleC-1'), (1, 'RuleA-3')
-- Create a break in IDENTITY values.. just to simulate more realistic data
INSERT INTO #tbl (Val) VALUES ('DeleteMe'), ('DeleteMe');
DELETE FROM #tbl WHERE Val = 'DeleteMe';
INSERT INTO #tbl (DocID, Val) VALUES (6, 'RuleE'), (7, 'RuleF');
SELECT * FROM #tbl t;
-- Declare TWO temp tables each with an IDENTITY - one will hold the RuleID of the items we are copying, other will hold the RuleID that we create
DECLARE #input table (RID int IDENTITY(1, 1), SourceRuleID int NOT NULL, Val varchar(100));
DECLARE #output table (RID int IDENTITY(1,1), TargetRuleID int NOT NULL, Val varchar(100));
-- Capture the IDs of the rows we will be copying by inserting them into the #input table
-- Important - we must specify the sort order - best thing is to use the IDENTITY of the source table (t.RuleID) that we are copying
INSERT INTO #input (SourceRuleID, Val) SELECT t.RuleID, t.Val FROM #tbl t WHERE t.DocID = 1 ORDER BY t.RuleID;
-- Copy the rows, and use the OUTPUT clause to capture the IDs of the inserted rows.
-- Important - we must use the same WHERE and ORDER BY clauses as above
INSERT INTO #tbl (DocID, Val)
OUTPUT Inserted.RuleID, Inserted.Val INTO #output(TargetRuleID, Val)
SELECT #newDocID, t.Val FROM #tbl t
WHERE t.DocID = 1
ORDER BY t.RuleID;
-- Now #input and #output should have the same # of rows, and the order of both inserts was the same, so the IDENTITY columns (RID) can be matched
-- Use this as the map from old-to-new when you are copying sub-table rows
-- Technically, #input and #output don't even need the 'Val' columns, just RID and RuleID - they were included here to prove that the rules matched
SELECT i.*, o.* FROM #output o
INNER JOIN #input i ON i.RID = o.RID
-- Confirm the matching worked
SELECT * FROM #tbl t

Help with T-SQL script: Insert record, then use identity of that insert on another statement?

Just as a preface, I'm not very knowledgeable on T-SQL syntax.
I'd like to create a simple SQL script that will make 3 insert statements.
Insert A
Insert B
Insert C
Insert A statement's identity or "ID" would be needed in insert B statement.
And both the identities Inserts A & B would be needed in Insert C statement.
Pseudo code would look something like:
INSERT INTO tableA
VALUES ('blah', 'blah')
INSERT INTO tableB
VALUES (IDENTITY_FROM_A_INSERT, 'foo')
INSERT INTO tableC
VALUES (IDENTITY_FROM_A_INSERT, IDENTITY_FROM_B_INSERT)
How would I go about writing this script?

Use SCOPE_IDENTITY() after each insert in order to get the identity of the inserted row (in the current session).
I have used two variables to capture the two identities and then insert them into the third table:
DECLARE #Id1 INT
DECLARE #Id2 INT
INSERT INTO tableA VALUES ('blah', 'blah')
SET #Id1 = SELECT SCOPE_IDENTITY()
INSERT INTO tableB VALUES (IDENTITY_FROM_A_INSERT, 'foo')
SET #Id2 = SELECT SCOPE_IDENTITY()
INSERT INTO tableC VALUES (#Id1, #Id2)

scope_identity() is perfect for integer identifiers on single-record insertions (+1 to the other answer btw). However, if you find yourself using a guid/uniqueidentifier (newsequentialid(), newid(), etc) or inserting multiple records at once, you'll need something a little different:
declare #id uniqueidentifier;
-- Table variable for storing your newly inserted identifiers:
declare #NewlyInsertedIds table
(
[Id] uniqueidentifier
);
insert [MyTable]
(
[Blah1]
,[Blah2]
)
-- in the output clause you can access the inserted/deleted pseudo tables:
ouptut inserted.[Id]
into #NewlyInsertedIDs
(
[Id]
)
values
(
'Blah'
,'Blah'
);
select
#id = [Id]
from #NewlyInsertedIds;
Check out the OUTPUT Clause for more information.