【Transact-SQL】计算整个表中所有值的出现的次数

一个表有3列，5行，那么一共有15个值，现在要计算整个表中所有值在表中出现的次数，不过这里表的列数是不确定的，上面的例子是3列，实际上也有可能是5列、20列，所以解决问题的步骤是这样的：

1、必须知道有多少列，然后构造动态语句，把这些列合并到一列中。

2、然后去重计算出所有的可能值。

3、最后计算每个值在表中出现了多少次。

 

if(OBJECT_ID('dbo.wc') is not null) 	drop table dbo.wc go   create table wc 	( 	a nvarchar(100), 	b nvarchar(100), 	c nvarchar(100) 	) 	 insert into wc values('1','2','3'),       ('a','f','d'),       ('2','b','c'),       (null,'c','w'),       ('3','d',null)   declare @temp table (cn nvarchar(100));  declare @i int = 1;  declare @v varchar(max)='';  declare @column varchar(100)='';  while @i <= ( 				select count(*) 				from sys.tables t 				inner join sys.columns c 						on t.object_id =c.object_id  				where t.name = 'wc'                 ) begin     select @column = c.name 	from sys.tables t 	inner join sys.columns c 			on t.object_id =c.object_id  	where t.name = 'wc' 	      and c.column_id = @i  	       	set @i = @i + 1           set @v = @v + ' select '+ @column + ' from wc union all'  end  select @v = LEFT(@v,len(@v)-LEN('union all')) --select @v  insert into @temp exec (@v)  ;with a as ( select cn from @temp where cn is not null group by cn )        select a.cn,        COUNT(t.cn) from a inner join @temp t         on a.cn = t.cn group by a.cn