sql server 查询表内所有列字段最大长度

DECLARE @tableName NVARCHAR(50)= 'tablename';
DECLARE @tmpTable TABLE
    (
      ColumnName NVARCHAR(50) NOT NULL PRIMARY KEY ,
      ColumnMaxLen INT NOT NULL
    );
INSERT  @tmpTable
        SELECT  COLUMN_NAME ,
                0
        FROM    INFORMATION_SCHEMA.COLUMNS
        WHERE   TABLE_NAME = @tableName;
DECLARE @columnName NVARCHAR(50);
DECLARE @columnMaxLen INT;
DECLARE @sql NVARCHAR(MAX);
DECLARE tmpCursor CURSOR
FOR
    SELECT  ColumnName
    FROM    @tmpTable FOR READ ONLY;
    
OPEN tmpCursor;
FETCH NEXT FROM tmpCursor INTO @columnName;
WHILE @@FETCH_STATUS = 0
    BEGIN
        SET @sql = 'SELECT @columnMaxLen=ISNULL(MAX(LEN([' + @columnName
            + '])), 0) FROM ' + @tableName;
     --   PRINT @sql;
        EXEC sp_executesql @sql, N'@columnMaxLen int out', @columnMaxLen OUT;
        UPDATE  @tmpTable
        SET     ColumnMaxLen = @columnMaxLen
        WHERE   ColumnName = @columnName;
        FETCH NEXT FROM tmpCursor INTO @columnName;
    END;
CLOSE tmpCursor;
DEALLOCATE tmpCursor;
SELECT  *
FROM    @tmpTable;