SQL: counting the number of different values ​​in each column

Question

I need a query that will return a table in which each column will count different values ​​in the columns of another table.

I can read individual values ​​in one column:

select count(distinct columnA) from table1;

I suppose I could just make this a very long select clause:

select count(distinct columnA), count(distinct columnB), ... from table1;

but it is not very elegant and hard-coded. I would prefer something more flexible.

Answer 1

. , , ( , , ) :

" 1" .

. : "select count ( A), count ( B),... 1".

Answer 2

( sql server 2005):

DECLARE @YourTable table (col1  varchar(5)
                         ,col2  int
                         ,col3  datetime
                         ,col4  char(3)
                         )

insert into @YourTable values ('abcdf',123,'1/1/2009','aaa')
insert into @YourTable values ('aaaaa',456,'1/2/2009','bbb')
insert into @YourTable values ('bbbbb',789,'1/3/2009','aaa')
insert into @YourTable values ('ccccc',789,'1/4/2009','bbb')
insert into @YourTable values ('aaaaa',789,'1/5/2009','aaa')
insert into @YourTable values ('abcdf',789,'1/6/2009','aaa')


;with RankedYourTable AS
(
SELECT
    ROW_NUMBER() OVER(PARTITION by col1 order by col1) AS col1Rank
        ,ROW_NUMBER() OVER(PARTITION by col2 order by col2) AS col2Rank
        ,ROW_NUMBER() OVER(PARTITION by col3 order by col3) AS col3Rank
        ,ROW_NUMBER() OVER(PARTITION by col4 order by col4) AS col4Rank
    FROM @YourTable
)
SELECT
    SUM(CASE WHEN      col1Rank=1 THEN 1 ELSE 0 END) AS col1DistinctCount
        ,SUM(CASE WHEN col2Rank=1 THEN 1 ELSE 0 END) AS col2DistinctCount
        ,SUM(CASE WHEN col3Rank=1 THEN 1 ELSE 0 END) AS col3DistinctCount
        ,SUM(CASE WHEN col4Rank=1 THEN 1 ELSE 0 END) AS col4DistinctCount
    FROM RankedYourTable

:

col1DistinctCount col2DistinctCount col3DistinctCount col4DistinctCount
----------------- ----------------- ----------------- -----------------
4                 3                 6                 2

(1 row(s) affected)

Answer 3

1 .

DECLARE @TableName VarChar (Max) = 'table1'
DECLARE @SqlString VarChar (Max)

set @SqlString = (
  SELECT DISTINCT
    'SELECT ' + 
        RIGHT (ColumnList, LEN (ColumnList)-1) + 
      ' FROM ' + Table_Name
    FROM INFORMATION_SCHEMA.COLUMNS COL1
      CROSS AppLy (
        SELECT ', COUNT (DISTINCT [' + COLUMN_NAME + ']) AS ' + '''' + COLUMN_NAME + ''''
          FROM INFORMATION_SCHEMA.COLUMNS COL2
          WHERE COL1.TABLE_NAME = COL2.TABLE_NAME
          FOR XML PATH ('')
      ) TableColumns (ColumnList)
    WHERE
      1=1 AND 
      COL1.TABLE_NAME = @TableName
)

EXECUTE (@SqlString)

Answer 4

and it is hard-coded.

It is not hardcoding to provide a list of fields for the sql statement. This is a common and acceptable practice.

Answer 5

This will not necessarily be possible for each field in the table. For example, you cannot make a DISTINCT with respect to a SQL Server text or graphic field unless you pass them to other data types and lose some precision.

Answer 6

DISTINCT is evil. Do COUNT / GROUP BY