SELECT 
  TABLE_NAME 表名,
  COLUMN_NAME 字段名,
  COLUMN_TYPE 字段类型,
  IS_NULLABLE 是否为空,
  COLUMN_DEFAULT 默认值,
  COLUMN_COMMENT 字段注释
FROM information_schema.COLUMNS 
WHERE TABLE_SCHEMA = '库名' 
-- AND TABLE_NAME = '指定表名'  -- 可只查某张表
ORDER BY TABLE_NAME,ORDINAL_POSITION;