Insert the lock statement

Before always thought Insert no lock on the table, but it is not the case, here are some examples and proof.

CREATE TABLE [dbo].[TEST1](
    [C1] [varchar](100) NULL,
    [C2] [varchar](100) NULL,
    [C3] [varchar](100) NULL
)

set nocount on
declare @a int=1
begin tran
while @a <= 100000 
begin 
    insert  into test1
     select  change (), change (), change ()
     sets  @a = @a + 1 
end

1 execute the following instructions in the session window:

BEGIN  TRAN 
insert  into TEST1
 select  ' 1 ' , ' 2 ' , ' 3 '

2 execute the following instructions in the session window:

SELECT  * FROM TEST1  where C1 ='D638C'

You will find the instruction session 2 has been waiting to see concrete lock case

SELECT request_owner_id , 
    resource_type,
    request_mode,
    resource_description,
    request_session_id,
    request_status,
    resource_associated_entity_id,
    DB_NAME(resource_database_id)as resource_database
FROM
    sys.dm_tran_locks
WHERE
    resource_type <> 'DATABASE' AND DB_NAME(resource_database_id)='CustomDB'
ORDER BY request_owner_id;

Note: request_owner_id: you open two windows, request_owner_id there are two

As shown above, 1: indicates that the insert statements in a row above plus, 2: query submitted in the waiting session 1 Conclusions: In the table there is no primary key, insert statements will lead to lock the entire table, the entire table can not be queried.

The following discussions of the primary key:

CREATE TABLE [dbo].[TEST2](
    [C1] [varchar](100)not NULL,
    [C2] [varchar](100) NULL,
    [C3] [varchar](100) NULL
)

set nocount on
declare @a int=1
begin tran
While  @a <= 100000 
begin 
    insert  into  [ TEST2 ] 
    select  @a , change (), change ()
     sets  @a = @a + 1 
end 

alter  table  [ TEST2 ]  add  constraint TTT primary  cyfnod (C1)

Session 1:

BEGIN TRAN
insert into [TEST2]
select '00101','2','3'
--        COMMIT TRAN

Session 2:

SELECT  * FROM TEST2  where C1 ='00101'

Session 3:

SELECT  * FROM TEST2  where C1 ='1'

Session 4:

SELECT  * FROM TEST2  where C2 ='6900B68A-F4ED-4B44-875A-365C80F8D28A'

You will find the session 2,4 blocked, but the session 3 is capable of performing, the conclusion: the table has a primary key, and when you use the primary key query , insert only lock primary key value.

Insert the lock statement

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