如何从列表中进行选择？ SQL Server

Question

我有一个通过SQL查询获得的列列表。

SELECT t.name AS table_name,
    SCHEMA_NAME(schema_id) AS schema_name,
    c.name AS column_name
FROM sys.tables AS t
INNER JOIN sys.columns c ON t.OBJECT_ID = c.OBJECT_ID
ORDER BY table_name

现在，对于每一列，我想查询有关该列的一些信息，并将它们放在一个表中。

例如，这是我将为单个列运行的查询。

Select Substring(col1, 1, 1) letter, Count(Substring(col1, 1, 1)) cnt
From tbl
Group By Substring(col1, 1, 1)

该子查询的作用是它获得列中记录的第一个字符的计数。 因此，例如，col1中可能有6个以字母'a'开头的记录，col1中有15个以字母'b'开头的记录，等等。

如何将这两个查询组合到一个表中，以便得到类似...

Table_Name, Column_Name, letter, cnt

    tbl, col1, a, 6

    tbl, col1, b, 15

    tbl, col2, a, 5

    ...

Answer 1

你要这个 ：

SELECT t.name AS table_name,
       c.name AS column_name, t1.letter, count(*) as cnt
FROM sys.tables AS t INNER JOIN 
     sys.columns c 
     ON t.OBJECT_ID = c.OBJECT_ID 
CROSS APPLY ( VALUES (Substring(c.name, 1, 1)) ) t1(letter)
GROUP BY t.name, c.name, t1.letter;

Answer 2

这有用吗？

DECLARE @query VARCHAR(Max)

SELECT @query=COALESCE(@query + ' union all ', '') + CAST('SELECT ''' +TABLE_SCHEMA+''' As [Schema],'''+TABLE_NAME+''' As TableName,'''+COLUMN_NAME+''' As ColumnName, Substring(['+COLUMN_NAME+'],1,1) letter,COUNT(Substring(['+COLUMN_NAME+'],1,1)) cnt
FROM '+TABLE_SCHEMA+'.'+TABLE_NAME+
' Group by Substring(['+COLUMN_NAME+'],1,1)' AS VARCHAR(MAX))
FROM INFORMATION_SCHEMA.COLUMNS
WHERE DATA_TYPE IN('varchar','char','nvarchar') 

--SELECT @query
Exec(@query)