錯誤：“無法識別的名稱：employees at [9:8]”

在使用表別名時，可能會遇到“無法識別的名稱：employees at [9:8]”錯誤。讓我們分析其原因並提供正確的解決方案。

錯誤分析：

在提供的SQL查詢中：

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別名：

ON employees.department_id = departments.department_id

但是，Employees和departments表在FROM子句中沒有明確定義別名。這導致了錯誤，因為BigQuery要求在使用別名之前必須定義它們。

解決方案：

要解決此錯誤，必須在使用別名之前定義它們：

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

通過在完整的表引用之後添加別名AS employees和AS departments，查詢現在可以正確識別表並執行，而不會出現錯誤。