sqlserver 查询表中所有字段的最大长度（转载）

转载来源：https://www.cnblogs.com/lizhanglong/p/6696722.html

DECLARE @tableName NVARCHAR(50)= 'home';
 
IF OBJECT_ID(N'TableColumnMaxLen', N'U') IS  NULL
    BEGIN
        CREATE TABLE TableColumnMaxLen
            (
              TableName NVARCHAR(50) NOT NULL ,
              ColumnName NVARCHAR(50) NOT NULL ,
              ColumnMaxLen INT NOT NULL ,
              PRIMARY KEY ( TableName, ColumnName )
            );
    END;
DECLARE @columnName NVARCHAR(50);
DECLARE @columnMaxLen INT;
DECLARE @sql NVARCHAR(MAX);
DECLARE @initState INT= -1;
DECLARE @searchingState INT= -2;
IF NOT EXISTS ( SELECT  1
                FROM    dbo.TableColumnMaxLen
                WHERE   TableName = @tableName )
    BEGIN
        INSERT  TableColumnMaxLen
                SELECT  @tableName ,
                        COLUMN_NAME ,
                        @initState
                FROM    INFORMATION_SCHEMA.COLUMNS
                WHERE   TABLE_NAME = @tableName;
    END;
 
WHILE 1 = 1
    BEGIN
        SET @columnName = ( SELECT TOP 1
                                    ColumnName
                            FROM    TableColumnMaxLen
                            WHERE   TableName = @tableName
                                    AND ColumnMaxLen = @initState
                          );
        IF @columnName IS NULL
            BREAK;
 
        UPDATE  TableColumnMaxLen
        SET     ColumnMaxLen = @searchingState
        WHERE   TableName = @tableName
                AND ColumnName = @columnName;
 
        SET @sql = 'SELECT @columnMaxLen=ISNULL(MAX(LEN([' + @columnName
            + '])), 0) FROM ' + @tableName;
      --  PRINT @sql;
        EXEC sp_executesql @sql, N'@columnMaxLen int out', @columnMaxLen OUT;
 
        UPDATE  TableColumnMaxLen
        SET     ColumnMaxLen = @columnMaxLen
        WHERE   TableName = @tableName
                AND ColumnName = @columnName;      
    END;
 
SELECT  *
FROM    TableColumnMaxLen
WHERE   TableName = @tableName;