输出子句解释

Question

请向我解释 SQL Server 输出子句。

Answer 1

Do some examples help? The below all output the result to the client but you can also OUTPUT INTO a @table_variable (or a standard table under certain conditions)

create table T
(
id int identity(1,1),
c char(1)
)

insert into T(c) 
OUTPUT inserted.* /*Output Inserted Rows - shows the ids that were allocated*/
values ('A'),('B'),('C')

Returns

id          c
----------- ----
1           A
2           B
3           C

.

UPDATE T
SET c = CHAR(ASCII(c)+1)
 /*Output before and after versions of each row*/
OUTPUT deleted.*, inserted.*
WHERE id IN (2,3)

Returns

id          c    id          c
----------- ---- ----------- ----
2           B    2           C
3           C    3           D

.

DELETE 
FROM T
 /*Output the row(s) that were deleted*/
OUTPUT deleted.*
WHERE DATEPART(second, getdate())%id = 0

Returns (for example)

id          c
----------- ----
1           A

Edit:

In response to comment some examples showing how OUTPUT can be used to insert to a table.

CREATE TABLE #T2
(
id UNIQUEIDENTIFIER DEFAULT NEWSEQUENTIALID(),
c CHAR(1)
)

DECLARE @inserted TABLE
(
id UNIQUEIDENTIFIER,
c CHAR(1)
)

INSERT INTO #T2(c) 
OUTPUT inserted.id, inserted.c 
INTO @inserted
VALUES ('A')

If you are on SQL Server 2008 you can use composable DML

INSERT INTO @inserted
SELECT I.id, I.c
FROM 
    (
    INSERT INTO #T2(c) 
    OUTPUT inserted.id, inserted.c 
    VALUES ('B'),('C')
    ) AS I
WHERE c <> 'C' --Only add rows of interest to @inserted table

But you will get an error message if the insert target participates in a PK/FK relationship. If you encounter this problem you can also use this pattern .

INSERT INTO @inserted
EXEC sp_executesql N'
    INSERT INTO #T2(c) 
    OUTPUT inserted.id, inserted.c 
    VALUES (''D''),(''E'') '

Answer 2

It could be stated as

How do I find out what rows were deleted, inserted or updated?

You can using some fancy trigger code or a separate SELECT, but the OUTPUT clause make it effortless. The SELECT becomes part of the actual DELETE, INSERT or UPDATE

Answer 3

The OUTPUT clause allows you to combine an INSERT or UPDATE with a SELECT .

You can OUTPUT a list of fields, and the query will return one row for each row affected by the INSERT / UPDATE .