错误：“无法识别的名称：employees at [9:8]”

在使用表别名时，可能会遇到“无法识别的名称：employees at [9:8]”错误。让我们分析其原因并提供正确的解决方案。

错误分析：

在提供的SQL查询中：

SELECT 
    employees.name AS employee_name,
    employees.role AS employee_role,
    departments.name AS department_name
FROM 
    `strange-calling-318804.employee_data.Employees`
    JOIN 
    `strange-calling-318804.employee_data.departments` 
    ON employees.department_id = departments.department_id

在ON子句中使用了employees和departments别名：

ON employees.department_id = departments.department_id

但是，Employees和departments表在FROM子句中没有明确定义别名。这导致了错误，因为BigQuery要求在使用别名之前必须定义它们。

解决方案：

要解决此错误，必须在使用别名之前定义它们：

SELECT 
    employees.name AS employee_name,
    employees.role AS employee_role,
    departments.name AS department_name
FROM 
    `strange-calling-318804.employee_data.Employees` AS employees
    JOIN 
    `strange-calling-318804.employee_data.departments` AS departments 
    ON employees.department_id = departments.department_id

通过在完整的表引用之后添加别名AS employees和AS departments，查询现在可以正确识别表并执行，而不会出现错误。