在BigQuery中，选择每个分组的第一行有几种方法，以下是其中两种：

方法1：

SELECT * FROM ( SELECT *, ROW_NUMBER() OVER(PARTITION BY column_to_group ORDER BY column_to_order) row_num FROM your_table ) WHERE row_num = 1

示例代码：

SELECT * FROM ( SELECT *, ROW_NUMBER() OVER(PARTITION BY country ORDER BY salary DESC) row_num FROM employees ) WHERE row_num = 1;

该代码将从employees表中选择每个国家的最高薪资。

方法2：

SELECT * FROM your_table WHERE column_to_order = ( SELECT MIN(column_to_order) FROM your_table WHERE column_to_group = your_table.column_to_group )

示例代码：

SELECT * FROM employees WHERE salary = ( SELECT MIN(salary) FROM employees WHERE country = employees.country );

该代码将从employees表中选择每个国家的最低薪资。