SQL Server查询选择某种类型的所有列，也表明

Question

我使用SQL Server 2012的

我查询的第一部分已经回答了这个thread其最大值。但是我也想要第二列显示相应表格中该列的相应最大值。

我试过这种方法：使用一个函数，它以表名和列名作为参数并返回最大值。但从函数使用动态SQL是非法的。此外，我似乎无法从一个SELECT查询中调用一个函数。

我也试过使用存储过程，但我无法弄清楚如何调用它并使用它。请建议替代方法来实现这一点。

我是SQL Server的新手。

感谢

Answer 1

您可以使用下面的SP和提高它按您的需求，

CRETE PROCEDURE Getmaxtablecolval 
AS 
    BEGIN 
     CREATE TABLE #t 
     (
      tablename VARCHAR(50), 
      columnname VARCHAR(50), 
      id   INT, 
      counts  INT 
     ) 

     INSERT INTO #t 
     SELECT table_name [Table Name], 
      column_name [Column Name], 
      NULL, 
      NULL 
     FROM information_schema.columns 
     WHERE data_type = 'INT' 

     BEGIN TRAN 

     DECLARE @id INT 

     SET @id = 0 

     UPDATE #t 
     SET @id = id = @id + 1 

     COMMIT TRAN 

     DECLARE @RowCount INT 

     SET @RowCount = (SELECT Count(0) 
         FROM #t) 

     DECLARE @I INT 

     SET @I = 1 

     DECLARE @Counter INT 
     DECLARE @TName VARCHAR(50) 
     DECLARE @CName VARCHAR(50) 
     DECLARE @DynamicSQL AS VARCHAR(500) 

     WHILE (@I <= @RowCount) 
     BEGIN 
      SELECT @TName = tablename 
      FROM #t 
      WHERE id = @I 

      SELECT @CName = columnname 
      FROM #t 
      WHERE id = @I 

      SET @DynamicSQL = 'Update #T Set Counts = ' 
           + '(Select ISNull(Max(' + @CName + '), 0) From ' 
           + @TName + ') Where Id = ' 
           + CONVERT(VARCHAR(10), @I) 

      --PRINT @DynamicSQL 
      EXEC (@DynamicSQL) 

      SET @I = @I + 1 
     END 

     SELECT * 
     FROM #t 
    END 

go 

Getmaxtablecolval 

Answer 2

您可以创建一个过程出这一点：

CREATE PROCEDURE GET_COLUMNS_WITH_MAX_VALUE 

    @COLUMN_TYPE NVARCHAR(50) 
AS 
BEGIN 
    -- SET NOCOUNT ON added to prevent extra result sets from 
    -- interfering with SELECT statements. 
    SET NOCOUNT ON; 

    -- DUMMY VARIABLE TO COPY STRUCTURE TO TEMP 
     DECLARE @DUMMY TABLE 
    (
     TABLE_NAME NVARCHAR(50), 
     COLUMN_NAME NVARCHAR(50), 
     MAX_VALUE NVARCHAR(MAX) 
    ) 

    -- CREATE TEMP TABLE FOR DYNAMIC SQL 
    SELECT TOP 0 * INTO #TABLE FROM @DUMMY 

    INSERT INTO #TABLE 
    (TABLE_NAME, COLUMN_NAME) 
    SELECT TABLE_NAME, COLUMN_NAME 
    FROM information_schema.columns where data_type = @COLUMN_TYPE 

    DECLARE @TABLE_NAME VARCHAR(50) -- database name 
    DECLARE @COLUMN_NAME VARCHAR(256) -- path for backup files 

    DECLARE db_cursor CURSOR FOR 
    SELECT TABLE_NAME, COLUMN_NAME 
    FROM #TABLE 

    OPEN db_cursor 
    FETCH NEXT FROM db_cursor INTO @TABLE_NAME, @COLUMN_NAME 

    WHILE @@FETCH_STATUS = 0 
    BEGIN 

    DECLARE @SQL NVARCHAR(MAX) = 'UPDATE #TABLE SET MAX_VALUE = (SELECT MAX([' + @COLUMN_NAME + ']) FROM [' + @TABLE_NAME + ']) ' 
           + 'WHERE [COLUMN_NAME] = ''' + @COLUMN_NAME + ''' AND TABLE_NAME = ''' + @TABLE_NAME + ''''; 
    PRINT @SQL 
    EXEC (@SQL) 

    FETCH NEXT FROM db_cursor INTO @TABLE_NAME, @COLUMN_NAME 

    END 

    CLOSE db_cursor 
    DEALLOCATE db_cursor 


    SELECT * FROM #TABLE 

    DROP TABLE #TABLE 

END 
GO 

用法：

​​ 个

结果：

TABLE1  ID  50 
TABLE2  ID  100 
TABLE3  CarID  20 
TABLE4  StudentID 30 

Answer 3

我认为最简单的解决办法是存储过程。据我所知：

• 动态SQL不能放置在功能
• 动态SQL不能发生在OPENROWSET

我另外，如果你写这样的程序：

• 谨防包含空格，qoutes（SQL注入可能的）名字的
• MAX在非索引列（列），将需要全扫描（可能会很慢）
• 表和列名可以被复制（放置在differend模式）

编号重复和性能是没有问题的，看看下面的代码片段：

CREATE PROC FindMaxColumnValues 
    @type sysname = '%', 
    @table sysname = '%' 
AS 
DECLARE @result TABLE (TableName sysname, ColumnName sysname, MaxValue NVARCHAR(MAX)) 

DECLARE @tab sysname 
DECLARE @col sysname 
DECLARE cur CURSOR FOR 
    SELECT TABLE_NAME TableName, COLUMN_NAME [Column Name] 
    FROM INFORMATION_SCHEMA.COLUMNS 
    WHERE DATA_TYPE LIKE @type and TABLE_NAME LIKE @table 

OPEN cur 

FETCH NEXT FROM cur INTO @tab, @col 
WHILE @@FETCH_STATUS = 0 
BEGIN 
    DECLARE @sql nvarchar(MAX) = 'SELECT '+QUOTENAME(@tab,'''')+' [TableName], '+QUOTENAME(@col, '''')+' [ColumnName], MAX('+QUOTENAME(@col)+') FROM '+QUOTENAME(@tab) 
    INSERT INTO @result EXEC(@sql) 
    FETCH NEXT FROM cur INTO @tab, @col 
END 

CLOSE cur 
DEALLOCATE cur 

SELECT * FROM @result 

样品：

--MAX of INT's 
EXEC FindMaxColumnValues 'INT' 
--MAX of INT's in tables matching 'TestTab%' 
EXEC FindMaxColumnValues 'INT', 'TestTab%' 
--MAX of ALL columns 
EXEC FindMaxColumnValues 

结果：

TableName ColumnName MaxValue 
IdNameTest ID   2 
TestTable ID   5 
TestTable Number  3 

TableName ColumnName MaxValue 
TestTable ID   5 
TestTable Number  3 

TableName  ColumnName MaxValue 
UpdateHistory UpdateTime 2016-07-14 12:21:37.00 
IdNameTest  ID   2 
IdNameTest  Name   T2 
TestTable  ID   5 
TestTable  Name   F 
TestTable  Number  3