1.查看所有表字段的（数据类型 + 长度描述 + 实际长度（字节））
SELECT s.name AS SchemaName,t.name AS TableName,c.name AS ColumnName,-- 数据类型 + 长度拼接（用于显示）ty.name +CASE WHEN ty.name IN ('char', 'varchar', 'nchar', 'nvarchar') THEN '(' + CASE WHEN c.max_length = -1 THEN 'MAX'ELSE CAST(CASE WHEN ty.name IN ('nchar', 'nvarchar') THEN c.max_length / 2ELSE c.max_lengthEND AS VARCHAR)END + ')'WHEN ty.name IN ('decimal', 'numeric') THEN '(' + CAST(c.precision AS VARCHAR) + ',' + CAST(c.scale AS VARCHAR) + ')'ELSE ''END AS DataTypeWithLength,-- 实际长度（字节）c.max_length AS ActualLengthBytes,c.is_nullableFROM sys.columns cINNER JOIN sys.tables t ON c.object_id = t.object_idINNER JOIN sys.schemas s ON t.schema_id = s.schema_idINNER JOIN sys.types ty ON c.user_type_id = ty.user_type_id
ORDER BY s.name, t.name, c.column_id;
说明：
SchemaName：表所属的 schema，例如 dbo
TableName：表名
ColumnName：字段名
DataTypeWithLength：数据类型及长度，如nvarchar(20)
is_nullable：是否允许 NULL(0代表否，1代表是)
2.如果你希望显示“字符长度”而不是字节数，可使用如下SQL
SELECT s.name AS SchemaName,t.name AS TableName,c.name AS ColumnName,-- 数据类型 + 长度/精度拼接ty.name +CASE WHEN ty.name IN ('char', 'varchar', 'nchar', 'nvarchar') THEN '(' + CASE WHEN c.max_length = -1 THEN 'MAX'ELSE CAST(CASE WHEN ty.name IN ('nchar', 'nvarchar') THEN c.max_length / 2ELSE c.max_lengthEND AS VARCHAR)END + ')'WHEN ty.name IN ('decimal', 'numeric') THEN '(' + CAST(c.precision AS VARCHAR) + ',' + CAST(c.scale AS VARCHAR) + ')'ELSE ''END AS DataTypeWithLength,-- 实际长度（字节）c.max_length AS ActualLengthBytes,-- 实际长度（字符数）CASE WHEN ty.name IN ('nchar', 'nvarchar') THEN CASE WHEN c.max_length = -1 THEN -1 ELSE c.max_length / 2 ENDELSE CASE WHEN c.max_length = -1 THEN -1 ELSE c.max_length ENDEND AS ActualLengthChars,-- 是否可为空c.is_nullableFROM sys.columns cINNER JOIN sys.tables t ON c.object_id = t.object_idINNER JOIN sys.schemas s ON t.schema_id = s.schema_idINNER JOIN sys.types ty ON c.user_type_id = ty.user_type_idORDER BY s.name, t.name, c.column_id;说明：
ActualLengthBytes：SQL Server 存储字段时使用的字节数
ActualLengthChars：你定义的字符数，比如 nvarchar(50) 实际为 50 字符，但占用 100 字节
MAX 类型会显示为 -1（表示可变最大）
