declare @tableName nvarchar(max)
set @tableName='table1,table2,table3,table4'

select substring(@tableName,number,charindex(',',@tableName+',',number)-number) tbn
from master..spt_values
where [type] = 'p' and number between 1 and len(@tableName)
    and substring(','+@tableName,number,1) = ','

/*********************************

tbn
----------------------------------------------------------------------------------------------------------------
table1
table2
table3
table4

(4 行受影响)

------解决方案--------------------
SQL code

declare @tableName nvarchar(max)
declare @sql varchar(max)
declare @DocEntry nvarchar(max)
set @tableName='table1,table2,table3,table4'
set @DocEntry = 'opq'

select @sql = isnull(@sql,'')+' delete from ' + tbn + ' where DocEntry = ''' + @DocEntry + '''' + char(13)
from(
    select substring(@tableName,number,charindex(',',@tableName+',',number)-number) tbn
    from master..spt_values
    where [type] = 'p' and number between 1 and len(@tableName)
        and substring(','+@tableName,number,1) = ','
)t

print @sql

/********************

 delete from table1 where DocEntry = 'opq'
 delete from table2 where DocEntry = 'opq'
 delete from table3 where DocEntry = 'opq'
 delete from table4 where DocEntry = 'opq'

------解决方案--------------------
SQL code

declare @tableName nvarchar(max)
declare @i int=1
set @tableName='table1,table2,table3,table4'

while(@i<=len(','+@tableName))
begin
 if substring(','+@tableName,@i,1)=','
   select substring(','+@tableName,@i+1,charindex(',',@tableName+',',@i+1)-@i) tb
 select @i=@i+1
end

-- 结果
tb
--------
table1

tb
--------
table2

tb
--------
table3

tb
--------
table4