Question

我的数据库中有两个表，看起来像这样

CREATE TABLE IF NOT EXISTS `lab_closure_states`
(
state_id INT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
lab_id INT UNSIGNED NOT NULL,
period_id INT UNSIGNED NOT NULL,
date DATE NOT NULL,
state BOOL NOT NULL
)  ENGINE = MYISAM 
DEFAULT CHARACTER SET = utf8 
COLLATE = utf8_bin;

CREATE TABLE IF NOT EXISTS `lab_appointments`
(
appointment_id INT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
created DATETIME NOT NULL,
user_id INT UNSIGNED NOT NULL,
lab_id INT UNSIGNED NOT NULL,
period_id INT UNSIGNED NOT NULL,
date DATE NOT NULL,
class_size INT UNSIGNED NOT NULL,
comment TEXT NOT NULL,
lab_is_closed BOOL NOT NULL
) ENGINE = MYISAM 
DEFAULT CHARACTER SET = utf8 
COLLATE = utf8_bin;

是否可以为状态不为假的给定用户选择所有约会？我遇到的复杂情况是，对于存在的每个lab_closure_state，我可能不一定有lab_appointment个条目。感谢

Answer 1

不是指对问题文本的严格答案，而是回答问题标题：

SELECT *
FROM lab_appointments root
LEFT OUTER JOIN lab_closure_states satellite 
    ON  satellite.lab_id = root.lab_id
    AND satellite.state = 0
WHERE 
    satellite.state_id IS NULL

上面显示的方法让您有机会在查询中链接多个卫星表，并通过在IS NULL语句中放置IS NOT NULL或WHERE来构建复杂的过滤条件。

根据多个表中的条目排除SQL查询的结果

1 个答案: