爲什麼我得到這個錯誤？語法錯誤或訪問衝突：1066不是唯一的表/別名：「員工」

Question

這裏是我的SQL查詢：

SELECT Employees.employee_id AS `Employees__employee_id`, 
    Employees.designation_id AS `Employees__designation_id`, 
    Employees.first_name AS `Employees__first_name`, 
    Employees.last_name AS `Employees__last_name`, 
    Employees.address AS `Employees__address`, 
    Employees.contact_no AS `Employees__contact_no`, 
    Employees.joining_date AS `Employees__joining_date`, 
    Employees.username AS `Employees__username`, 
    Employees.password AS `Employees__password`, 
    Employees.basic_pay AS `Employees__basic_pay`, 
    Employees.create_date AS `Employees__create_date`, 
    Employees.status AS `Employees__status`, 
    Designations.designation_id AS `Designations__designation_id`, 
    Designations.designation_name AS `Designations__designation_name`, 
    Designations.description AS `Designations__description` 
FROM employees Employees 
INNER JOIN employees Employees 
    ON Employees.employee_id = (Employees.employee_id) 
INNER JOIN designations Designations 
    ON Designations.designation_id = (Employees.designation_id) 
LIMIT 20 OFFSET 0 

我得到的錯誤是：

Error: SQLSTATE[42000]: Syntax error or access violation: 1066 Not unique table/alias: 'Employees'!

你能不能幫我在這。

Answer 1

對於查詢中的多個表，不能使用相同的別名（Employees）。在這裏，您在from和join子句中都使用它。只要在其中一個別名中使用不同的別名，你應該沒問題。

Answer 2

在你FROM條款你設置一個表的別名Employees一樣長OK爲你的MySQL在INNER JOIN條款運行大小寫敏感（在Linux或Unix等），或者如果您在Windows上運行它可能會失敗，但後來你使用相同的別名加入表格。這是一個重複的別名。 SQL不允許出現重複的別名，否則，例如，在調用Employees.designation_id時，它不會從應該評估哪個表中知道表達式。

無論您是否加入相同的表格，主表格和連接表格的表別名都必須不同。

更新：也許你不需要再次加入同一張表。刪除inner join employees部分：

SELECT Employees.employee_id AS `Employees__employee_id`, 
    Employees.designation_id AS `Employees__designation_id`, 
    Employees.first_name AS `Employees__first_name`, 
    Employees.last_name AS `Employees__last_name`, 
    Employees.address AS `Employees__address`, 
    Employees.contact_no AS `Employees__contact_no`, 
    Employees.joining_date AS `Employees__joining_date`, 
    Employees.username AS `Employees__username`, 
    Employees.password AS `Employees__password`, 
    Employees.basic_pay AS `Employees__basic_pay`, 
    Employees.create_date AS `Employees__create_date`, 
    Employees.status AS `Employees__status`, 
    Designations.designation_id AS `Designations__designation_id`, 
    Designations.designation_name AS `Designations__designation_name`, 
    Designations.description AS `Designations__description` 
FROM employees Employees 

INNER JOIN designations Designations 
    ON Designations.designation_id = (Employees.designation_id) 
LIMIT 20 OFFSET 0