SQL INSERT 但避免重复

Question

我想做一些快速插入，但避免在表中重复。为了便于讨论，我们将其称为 MarketPrices，我一直在尝试两种方法，但不确定如何进行基准测试，哪种方法会更快。

INSERT INTO MarketPrices (SecurityCode, BuyPrice, SellPrice, IsMarketOpen)
SELECT @SecurityCode, @BuyPrice,  @SellPrice, @IsMarketOpen
EXCEPT
SELECT SecurityCode, BuyPrice, SellPrice, j.bool as IsActive FROM MarketPrices
CROSS JOIN (SELECT 0 as bool UNION SELECT 1 as bool ) as j

或者

DECLARE @MktId int
SET @MktId = (SELECT SecurityId FROM MarketPrices 
              where SecurityCode = @SecurityCode 
              and BuyPrice=@BuyPrice 
              and SellPrice = @SellPrice)

IF (@MktId is NULL)  
BEGIN
    INSERT INTO MarketPrices (SecurityCode, BuyPrice, SellPrice, IsMarketOpen)
    VALUES
    (@SecurityCode,@BuyPrice, @SellPrice, @IsMarketOpen)
END

假设@whatever是存储过程中的输入参数。

当 BuyPrice 或 SellPrice 或两者与之前发生的所有其他情况不同时，我希望能够为每个 SecurityCode 插入一条新记录。我不关心 IsMarketOpen。​​

上述两种方法有什么明显愚蠢的地方吗？一个比另一个快吗？

Answer 1

编辑:防止race conditions在并发环境中，在相关子查询中使用 WITH (UPDLOCK) 或使用 EXCEPT'd SELECT。我下面编写的测试脚本不需要它，因为它使用仅对当前连接可见的临时表，但在真实环境中，针对用户表进行操作，这是必要的。

MERGE 不需要 UPDLOCK。

<小时/>

受到 mcl 的回答:唯一索引 & 让数据库抛出错误的启发，我决定进行基准测试 conditional inserts与 try/catch 。

结果似乎支持 try/catch 上的条件插入，但是 YMMV。这是一个非常简单的场景(一列，小表等)，在一台机器上执行，等等。

以下是结果(SQL Server 2008，内部版本 10.0.1600.2):

duplicates (short table)    
  try/catch:                14440 milliseconds / 100000 inserts
  conditional insert:        2983 milliseconds / 100000 inserts
  except:                    2966 milliseconds / 100000 inserts
  merge:                     2983 milliseconds / 100000 inserts

uniques
  try/catch:                 3920 milliseconds / 100000 inserts
  conditional insert:        3860 milliseconds / 100000 inserts
  except:                    3873 milliseconds / 100000 inserts
  merge:                     3890 milliseconds / 100000 inserts

  straight insert:           3173 milliseconds / 100000 inserts

duplicates (tall table)
  try/catch:                14436 milliseconds / 100000 inserts
  conditional insert:        3063 milliseconds / 100000 inserts
  except:                    3063 milliseconds / 100000 inserts
  merge:                     3030 milliseconds / 100000 inserts

请注意，即使对于唯一的插入，尝试/捕获的开销也会比条件插入稍微多一些。我想知道这是否因版本、CPU、核心数量等而异。

我没有对 IF 条件插入进行基准测试，只是对 WHERE 进行基准测试。我假设 IF 类型会显示更多开销，因为 a) 您是否有两个语句，b) 您需要将这两个语句包装在一个事务中并将隔离级别设置为可序列化(!) 。如果有人想要测试这一点，您需要将临时表更改为常规用户表(可序列化不适用于本地临时表)。

这是脚本:

-- tested on SQL 2008.
-- to run on SQL 2005, comment out the statements using MERGE
set nocount on

if object_id('tempdb..#temp') is not null drop table #temp
create table #temp (col1 int primary key)
go

-------------------------------------------------------

-- duplicate insert test against a table w/ 1 record

-------------------------------------------------------

insert #temp values (1)
go

declare @x int, @y int, @now datetime, @duration int
select @x = 1, @y = 0, @now = getdate()
while @y < 100000 begin
  set @y = @y+1
  begin try 
    insert #temp select @x
  end try
  begin catch end catch
end
set @duration = datediff(ms,@now,getdate())
raiserror('duplicates (short table), try/catch: %i milliseconds / %i inserts',-1,-1,@duration,@y) with nowait
go

declare @x int, @y int, @now datetime, @duration int
select @x = 1, @y = 0, @now = getdate()
while @y < 100000 begin
  set @y = @y+1
  insert #temp select @x where not exists (select * from #temp where col1 = @x)
end
set @duration = datediff(ms,@now,getdate())
raiserror('duplicates (short table), conditional insert: %i milliseconds / %i inserts',-1,-1,@duration, @y) with nowait
go

declare @x int, @y int, @now datetime, @duration int
select @x = 1, @y = 0, @now = getdate()
while @y < 100000 begin
  set @y = @y+1
  insert #temp select @x except select col1 from #temp
end
set @duration = datediff(ms,@now,getdate())
raiserror('duplicates (short table), except: %i milliseconds / %i inserts',-1,-1,@duration, @y) with nowait
go

-- comment this batch out for SQL 2005
declare @x int, @y int, @now datetime, @duration int
select @x = 1, @y = 0, @now = getdate()
while @y < 100000 begin
  set @y = @y+1
  merge #temp t using (select @x) s (col1) on t.col1 = s.col1 when not matched by target then insert values (col1);
end
set @duration = datediff(ms,@now,getdate())
raiserror('duplicates (short table), merge: %i milliseconds / %i inserts',-1,-1,@duration, @y) with nowait
go

-------------------------------------------------------

-- unique insert test against an initially empty table

-------------------------------------------------------

truncate table #temp
declare @x int, @now datetime, @duration int
select @x = 0, @now = getdate()
while @x < 100000 begin
  set @x = @x+1
  insert #temp select @x
end
set @duration = datediff(ms,@now,getdate())
raiserror('uniques, straight insert: %i milliseconds / %i inserts',-1,-1,@duration, @x) with nowait
go

truncate table #temp
declare @x int, @now datetime, @duration int
select @x = 0, @now = getdate()
while @x < 100000 begin
  set @x = @x+1
  begin try 
    insert #temp select @x
  end try
  begin catch end catch
end
set @duration = datediff(ms,@now,getdate())
raiserror('uniques, try/catch: %i milliseconds / %i inserts',-1,-1,@duration, @x) with nowait
go

truncate table #temp
declare @x int, @now datetime, @duration int
select @x = 0, @now = getdate()
while @x < 100000 begin
  set @x = @x+1
  insert #temp select @x where not exists (select * from #temp where col1 = @x)
end
set @duration = datediff(ms,@now,getdate())
raiserror('uniques, conditional insert: %i milliseconds / %i inserts',-1,-1,@duration, @x) with nowait
go

truncate table #temp
declare @x int, @now datetime, @duration int
select @x = 0, @now = getdate()
while @x < 100000 begin
  set @x = @x+1
  insert #temp select @x except select col1 from #temp
end
set @duration = datediff(ms,@now,getdate())
raiserror('uniques, except: %i milliseconds / %i inserts',-1,-1,@duration, @x) with nowait
go

-- comment this batch out for SQL 2005
truncate table #temp
declare @x int, @now datetime, @duration int
select @x = 1, @now = getdate()
while @x < 100000 begin
  set @x = @x+1
  merge #temp t using (select @x) s (col1) on t.col1 = s.col1 when not matched by target then insert values (col1);
end
set @duration = datediff(ms,@now,getdate())
raiserror('uniques, merge: %i milliseconds / %i inserts',-1,-1,@duration, @x) with nowait
go

-------------------------------------------------------

-- duplicate insert test against a table w/ 100000 records

-------------------------------------------------------

declare @x int, @y int, @now datetime, @duration int
select @x = 1, @y = 0, @now = getdate()
while @y < 100000 begin
  set @y = @y+1
  begin try 
    insert #temp select @x
  end try
  begin catch end catch
end
set @duration = datediff(ms,@now,getdate())
raiserror('duplicates (tall table), try/catch: %i milliseconds / %i inserts',-1,-1,@duration,@y) with nowait
go

declare @x int, @y int, @now datetime, @duration int
select @x = 1, @y = 0, @now = getdate()
while @y < 100000 begin
  set @y = @y+1
  insert #temp select @x where not exists (select * from #temp where col1 = @x)
end
set @duration = datediff(ms,@now,getdate())
raiserror('duplicates (tall table), conditional insert: %i milliseconds / %i inserts',-1,-1,@duration, @y) with nowait
go

declare @x int, @y int, @now datetime, @duration int
select @x = 1, @y = 0, @now = getdate()
while @y < 100000 begin
  set @y = @y+1
  insert #temp select @x except select col1 from #temp
end
set @duration = datediff(ms,@now,getdate())
raiserror('duplicates (tall table), except: %i milliseconds / %i inserts',-1,-1,@duration, @y) with nowait
go

-- comment this batch out for SQL 2005
declare @x int, @y int, @now datetime, @duration int
select @x = 1, @y = 0, @now = getdate()
while @y < 100000 begin
  set @y = @y+1
  merge #temp t using (select @x) s (col1) on t.col1 = s.col1 when not matched by target then insert values (col1);
end
set @duration = datediff(ms,@now,getdate())
raiserror('duplicates (tall table), merge: %i milliseconds / %i inserts',-1,-1,@duration, @y) with nowait
go