列が存在していてもオン句の未知の列

Question

次のMySQL 5.7.19スクリプトでは、エラーError Code: 1054. Unknown column 'ps.employeeId' in 'on clause'が発生します。

SELECT 
    `ps`.`employeeId` 
FROM 
    tablePS AS `ps`, 
    tableFO AS `fo` 
LEFT JOIN 
    tableWA AS `wa` 
ON 
    `wa`.`employeeId` = `ps`.`employeeId` 

スクリプトがエラーなしで実行私はFROM句

, 
     tableFO AS `fo` 

又は

`wa`.`employeeId` = 4 

でON句を

`wa`.`employeeId` = `ps`.`employeeId` 

を置き換える第二のテーブルを削除でありますあなたはこれらの共同でテーブルを作成することができますmmand

CREATE TABLE tablePS (
    `id` INT UNSIGNED auto_increment, 
    `employeeId` INT UNSIGNED, 
    PRIMARY KEY `id` (`id`) 
); 

CREATE TABLE tableFO (
    `id` INT UNSIGNED auto_increment, 
    PRIMARY KEY `id` (`id`) 
); 

CREATE TABLE tableWA (
    `id` INT UNSIGNED auto_increment, 
    `employeeId` INT UNSIGNED, 
    PRIMARY KEY `id` (`id`) 
); 

何が問題なのですか。

Answer 1

は

SELECT 
    `ps`.`employeeId` 
FROM 
    tablePS AS `ps` 
CROSS JOIN 
    tableFO AS `fo` 
LEFT JOIN 
    tableWA AS `wa` 
ON 
    `wa`.`employeeId` = `ps`.`employeeId`