使用Apache Beam和BigQuery表读取的解决方法包括以下步骤：

1. 安装Apache Beam和相关依赖：

pip install apache-beam[gcp]

2. 导入所需的模块：

import apache_beam as beam
from apache_beam.options.pipeline_options import PipelineOptions

3. 创建一个PipelineOptions对象，指定运行Beam的参数：

pipeline_options = PipelineOptions(
    runner='DataflowRunner',
    project='your-project-id',
    temp_location='gs://your-bucket/temp',
    staging_location='gs://your-bucket/staging'
)

4. 创建一个Pipeline对象：

p = beam.Pipeline(options=pipeline_options)

5. 使用ReadFromBigQuery方法从BigQuery表中读取数据：

table = 'your-project-id:your-dataset.your-table'
query = 'SELECT * FROM `{}`'.format(table)

data = p | 'ReadFromBigQuery' >> beam.io.ReadFromBigQuery(
    query=query,
    use_standard_sql=True
)

6. 使用WriteToText方法将数据写入文本文件：

output_path = 'gs://your-bucket/output.txt'

data | 'WriteToText' >> beam.io.WriteToText(output_path)

7. 运行Pipeline：

result = p.run()
result.wait_until_finish()

完整的代码示例如下所示：

import apache_beam as beam
from apache_beam.options.pipeline_options import PipelineOptions

pipeline_options = PipelineOptions(
    runner='DataflowRunner',
    project='your-project-id',
    temp_location='gs://your-bucket/temp',
    staging_location='gs://your-bucket/staging'
)

p = beam.Pipeline(options=pipeline_options)

table = 'your-project-id:your-dataset.your-table'
query = 'SELECT * FROM `{}`'.format(table)

data = p | 'ReadFromBigQuery' >> beam.io.ReadFromBigQuery(
    query=query,
    use_standard_sql=True
)

output_path = 'gs://your-bucket/output.txt'

data | 'WriteToText' >> beam.io.WriteToText(output_path)

result = p.run()
result.wait_until_finish()

请根据实际情况替换your-project-id，your-bucket，your-dataset和your-table。