在 TSQL 触发器中读取插入的列名和值

Question

我被要求为数据库中的每个表创建历史表。然后创建一个触发器，该触发器将在主表更新时写入历史表。

历史表的结构与主表相同，但多了几行（'id' 和 'update type'）

我以前从未对触发器做过任何事情，但我想做的是动态遍历“已插入”中的列并构造一个插入语句来填充历史记录表。

但是我不知道如何读取列的名称及其各自的值。

我的半成品触发器目前看起来像......

CREATE TRIGGER tr_address_history
ON address
FOR UPDATE
AS

DECLARE @colCount int
DECLARE @maxCols int
SET @colCount = 0
SET @maxCols = (SELECT COUNT(column_name) FROM INFORMATION_SCHEMA.columns WHERE TABLE_NAME = 'Inserted')

PRINT 'Number of columns = ' + CONVERT(varChar(10),@maxCols)
WHILE (@colCount <= @maxCols)
BEGIN
    DECLARE @name varchar(255)
    SELECT @name = column_name FROM INFORMATION_SCHEMA.columns WHERE TABLE_NAME = 'Inserted'
    DECLARE @value varchar(255)
    SELECT @value = @name FROM Inserted

    PRINT 'name = ' + @name + ' and value = ' + @value
    SET @colCount = @colCount + 1
END
PRINT 'Done';

当触发器运行时，它只会显示“列数 = 0”

谁能告诉我有什么问题：

SELECT COUNT(column_name) FROM INFORMATION_SCHEMA.columns WHERE TABLE_NAME = 'Inserted'

谢谢...

Answer 1

Beenay25 提出的第一个解决方案很好，但您应该使用受影响的表而不是“插入”伪表。

这是：

SELECT @name = column_name FROM INFORMATION_SCHEMA.columns WHERE TABLE_NAME = 'AFFECTED_TABLE'

而不是“插入”

另外，您应该使用动态 SQL。

这将是一个完整的工作解决方案：

ALTER TRIGGER [dbo].[tr_address_history]
ON [dbo].[address]
AFTER Insert
AS

DECLARE @ColumnName nvarchar(500)
DECLARE @TableName nvarchar(500)
DECLARE @value nvarchar(500)
DECLARE @Sql nvarchar(500)

Set @TableName='address'

DECLARE ColumnsCursor CURSOR FOR
select column_name FROM INFORMATION_SCHEMA.columns WHERE TABLE_NAME = 'address'

OPEN ColumnsCursor
FETCH NEXT FROM ColumnsCursor into @ColumnName

WHILE @@FETCH_STATUS=0
BEGIN 

      select * into #tmp from inserted
      Set @Sql= 'SELECT @value =' + @ColumnName + ' FROM #tmp'

      EXEC sp_executesql @Sql, N'@Value nvarchar(500) OUTPUT', @Value OUTPUT

      DROP TABLE #TMP

      print '[' + @ColumnName +'='+ ltrim(rtrim(@Value))+']'

      FETCH NEXT FROM ColumnsCursor into @ColumnName
END   

CLOSE ColumnsCursor
DEALLOCATE ColumnsCursor

Answer 2

'inserted' 表是一个伪表；它没有出现在 INFORMATION_SCHEMA 中。

有UPDATE() 运算符用于触发器：

CREATE TRIGGER trigger_name ON tablename
FOR UPDATE
AS
SET NOCOUNT ON
IF (UPDATE(Column1) OR UPDATE(Column2))
BEGIN
  your sql here
END

COLUMNS_UPDATED

UPDATE()

Answer 3

有一种方法可以满足提问者的要求：

我在触发器中做了一些事情，测试特定表的所有列是否实际参与了对该表的插入。如果他们这样做了，我后来将它们复制到历史表中。如果没有，则回滚并仅打印完整的行可能会插入到报告表中。也许他们可以根据自己的需要进行调整：

这里是：

    [

if exists (select 1 from inserted) and not exists (select 1 from deleted) -- if an insert has been performed
begin -- and we want to test whether all the columns in the report table were included in the insert
declare @inserted_columncount int, @actual_num_of_columns int, @loop_columns int, @current_columnname nvarchar(300),
    @sql_test nvarchar(max), @params nvarchar(max), @is_there bit
set @actual_num_of_columns = (
    select count(*) from (
    select COLUMN_NAME
    from INFORMATION_SCHEMA.COLUMNS
    where TABLE_NAME = 'renameFilesFromTable_report') as z)
set @inserted_columncount = 0
set @loop_columns = 1
declare inserted_columnnames cursor scroll for -- these are not really the inserted ones, but we are going to test them 1 by 1
    select COLUMN_NAME
    from INFORMATION_SCHEMA.COLUMNS
    where TABLE_NAME = 'renameFilesFromTable_report'
set @params = '@is_there_in bit output'
open inserted_columnnames
fetch next from inserted_columnnames into @current_columnname
select * into #temp_for_dynamic_sql from inserted -- this is necessary because the scope of sp_executesql does not include inserted pseudo table
while (@loop_columns <= @actual_num_of_columns) -- looping with independent integer arithmetic
begin
set @sql_test = '
set @is_there_in = 0
if exists (select ['+@current_columnname+'] from #temp_for_dynamic_sql where ['+@current_columnname+'] is not null)
set @is_there_in = 1'
exec sp_executesql @sql_test, @params, @is_there output
if @is_there = 1
begin
fetch next from inserted_columnnames into @current_columnname
set @inserted_columncount = @inserted_columncount + 1
set @loop_columns = @loop_columns + 1
end
else if @is_there <> 1
begin
fetch next from inserted_columnnames into @current_columnname
set @loop_columns = @loop_columns + 1
end
end 
close inserted_columnnames
deallocate inserted_columnnames
-- at this point we hold in two int variables the number of columns participating in the insert and the total number of columns

    ]

如果@inserted_columncount

我这样做是因为我有一个 sp 每次运行时都会在报表表中插入 1 个完整的行。没关系，但我不希望其他人误触那张桌子。连我自己都没有。我也想保留历史。所以我做了这个触发器来保留历史记录，但也检查是否尝试插入而没有报告表中所有列的值，并进一步检查代码是否尝试更新或删除并回滚。

我正在考虑扩展它以允许更新，但其中所有列都已设置。 这可以按如下方式完成：

如果尝试更新，

and exists (
select possibly_excluded.COLUMN_NAME from (
select COLUMN_NAME
from INFORMATION_SCHEMA.COLUMNS
where TABLE_NAME = 'renameFilesFromTable_report') as possibly_excluded
group by possibly_excluded.COLUMN_NAME
having COLUMN_NAME not in (
select COLUMN_NAME
from INFORMATION_SCHEMA.COLUMNS
where TABLE_NAME = 'renameFilesFromTable_report' and
sys.fn_IsBitSetInBitmask(@ColumnsUpdated, COLUMNPROPERTY(OBJECT_ID(TABLE_SCHEMA + '.' + TABLE_NAME), COLUMN_NAME, 'ColumnID')) <> 0)
)
begin
rollback transaction
print 'Only updates that set the values for a complete row are allowed on the report table..'
end