如何在各种文本字段中找到一行中最长的字符串？

Question

有没有人可以通过简单的查询从单个 SQL Server 2008 R2 数据库中所有表的所有字母数字（文本、nchar、varchar 等）类型的列中查找数据行中最长的字符串？

Answer 1

以下代码应返回具有当前数据库中最大文本段的单个列，以及架构、表和列名称以及文本段的大小：

DECLARE @cmd NVARCHAR(max);
DECLARE @sep NVARCHAR(max);
SET @cmd = '';
SET @sep = '';
SELECT @cmd = @cmd + @sep +
    'SELECT ''' + QUOTENAME(sc.name) + '.' + QUOTENAME(t.name) + 
    '.' + QUOTENAME(c.name) + ''' AS ColumnName, ' + 
    QUOTENAME(c.name) + ' AS ColumnValue, LEN(CAST(' + 
    QUOTENAME(c.name) + ' AS NVARCHAR(max))) AS ColumnLength ' +
    ' FROM ' + QUOTENAME(sc.name) + '.' + QUOTENAME(t.name)
    , @sep = ' UNION ALL '   
FROM sys.tables t 
    INNER JOIN sys.columns c ON t.object_id = c.object_id
    INNER JOIN sys.types ty on c.system_type_id = ty.system_type_id
    INNER JOIN sys.schemas sc ON t.schema_id = sc.schema_id
WHERE t.is_ms_shipped = 0
    AND ty.name IN (
        'ntext'
        , 'text'
        , 'varchar'
        , 'nvarchar'
        , 'nchar'
        , 'char'
        , 'sysname'
        , 'sql_variant'
        );
SET @cmd = 'SELECT TOP(1) * FROM (' + @cmd + ') t ORDER BY 3 DESC'
SELECT @cmd; /* This displays the resulting SQL Text that will be 
            EXEC'd by the following statement */
EXEC sp_executesql @cmd;