Question

通过做一些研究，似乎不可能使用where子句进行插入？我有一个表我想导入另一个表，其中特定的记录标准尚不存在。我该怎么做呢？

E.g伪代码 -

insert into table b (select * from table a) where not exists tableb.column1 = tablea.column1 and tableb.column2 = tablea.column2

这可能是通过加入来完成的吗？

Answer 1

您可以使用INSERT INTO.. SELECT NOT EXISTS进行插入。

<强>查询

insert into [TableB]
select * from [TableA] as [t1] -- [TableA] and [TableB] structure should be same.
where not exists(
    select 1 from [TableB] as [t2]
    where [t1].[column1] = [t2].[column1]
    and [t1].[column2] = [t2].[column2]
);

或者，如果表结构不相同且需要相同的几列，那么

<强>查询

insert into [TableB]([column1], [column2], ..., [columnN])
select [column1], [column2], ..., [columnN] 
from [TableA] as [t1]
where not exists(
    select 1 from [TableB] as [t2]
    where [t1].[column1] = [t2].[column1]
    and [t1].[column2] = [t2].[column2]
);

Answer 2

您还可以将LEFT JOIN与IS NULL一起使用，如下所示：

INSERT INTO tableb
SELECT a.* 
FROM tablea a
LEFT JOIN tableb b ON b.column1 = a.column1 
    AND b.column2 = a.column2
WHERE b.column1 IS NULL

Answer 3

在SELECT部分中从INSERT语句引用表名将不起作用，因为INSERT本身不是查询，但是没有什么可以阻止在SELECT中查询目标表，从而生成要插入的数据集。

    INSERT INTO tableb (column1, column2)
    SELECT column1, column2 FROM tablea 
    WHERE NOT EXISTS (SELECT * FROM tableb 
                      WHERE tableb.column1 = tablea.column1 
                      AND tabled.column2 = tablea.column2)

Answer 4

试试这个：

通过选择不存在的语句

进行插入

Declare @table1 table(Id int , EmpName varchar(100) )
Declare @table2 table(Id int , EmpName varchar(100) )

Insert into @table1 values (1,'Ajay'), (2, 'Tarak') , (3,'Nirav')

Insert into @table2 values (1,'Ajay')

--Insert into table b (select * from table a) where not exists tableb.column1 = tablea.column1 and tabled.column2 = tablea.column2 
INSERT INTO @table2 (id, empname)
   select id, empname from @table1
   EXCEPT
   SELECT id, empname from @table2


Select * from @table1
Select * from @table2

通过合并

Insert into @table2 values (4,'Prakash')
Select * from @table1
Select * from @table2


Declare @Id int , @EmpName varchar(100)
;with data as (select @id as id, @empname as empname from @table1)
   merge @table2 t
   using data s
      on s.id = t.id
     and s.empname = t.empname    
    when not matched by target
    then insert (id, empname) values (s.id, s.empname);


Select * from @table1
Select * from @table2

如果不存在，则根据另一个表插入表

4 个答案: