MySQL 视图使用 AND 会返回更多结果？

Question

当我这样做时：

select * from vw_active_employees where division IS NULL; --319 results

有道理。然后，我就这样做了……

select * from vw_active_employees where division IS NULL AND udds IS NULL; -- over 1000 results

什么啊？？更多结果？？

因此，我必须将视图包装为子选择，以便它返回我所期望的。像这样：

select vw_active_employees.* from (select * from vw_active_employees) tmp where division IS NULL AND udds IS NULL; --317 results

有人能解释一下吗？我从来没有在 MS SQLSERVER 中这样做过——所以这对我来说是陌生的。

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用于创建此视图的 SQL 实际上将许多其他视图连接在一起。我不完全确定它是否有帮助，但你要求它:) 基本上是

CREATE VIEW `vw_active_employees` AS

select 
e.*, 
`vw_employee_attributes_map`.`med_school_faculty`, `vw_employee_attributes_map`.`paid_clinic_faculty`, `vw_employee_attributes_map`.`volunteer_clinic_faculty`, `vw_employee_attributes_map`.`dept_vote_rights`, `vw_employee_attributes_map`.`emeritus`, `vw_employee_attributes_map`.`aoa_member`, `vw_employee_attributes_map`.`faculty_senate`, `vw_employee_attributes_map`.`faculty_senator_elect`, `vw_employee_attributes_map`.`faculty_senator_alt_elect`, `vw_employee_attributes_map`.`exec_comm_member`, `vw_employee_attributes_map`.`ucc`, `vw_employee_attributes_map`.`icc`, `vw_employee_attributes_map`.`va`, `vw_employee_attributes_map`.`uwmf`, `vw_employee_attributes_map`.`affiliate`, `vw_employee_attributes_map`.`aurora`, `vw_employee_attributes_map`.`website_searchable`,
`vw_employee_current_appointment_info`.`termination_date`, `vw_employee_current_appointment_info`.`last_promotion_date`, `vw_employee_current_appointment_info`.`promotion_due_date`, `vw_employee_current_appointment_info`.`last_reappointment_date`, `vw_employee_current_appointment_info`.`reappointment_duration`, `vw_employee_current_appointment_info`.`reappointment_due_date`, `vw_employee_current_appointment_info`.`non_renewal_date`, `vw_employee_current_appointment_info`.`roster`, `vw_employee_current_appointment_info`.`payroll`, `vw_employee_current_appointment_info`.`on_probation`, `vw_employee_current_appointment_info`.`probation_complete`, `vw_employee_current_appointment_info`.`probation_notify_sent_date`, `vw_employee_current_appointment_info`.`probation_end_date`, `vw_employee_current_appointment_info`.`uw_appointment_id`, `vw_employee_current_appointment_info`.`effective_date`, `vw_employee_current_appointment_info`.`percent`, `vw_employee_current_appointment_info`.`end_date`, `vw_employee_current_appointment_info`.`continuity_status`, `vw_employee_current_appointment_info`.`guaranteed_length`, `vw_employee_current_appointment_info`.`end_reason`, `vw_employee_current_appointment_info`.`midterm_eval_received`, `vw_employee_current_appointment_info`.`final_eval_received`, `vw_employee_current_appointment_info`.`annual_eval_letter_sent`, `vw_employee_current_appointment_info`.`annual_eval_sent_date`, `vw_employee_current_appointment_info`.`annual_eval_received`, `vw_employee_current_appointment_info`.`annual_eval_received_date`, `vw_employee_current_appointment_info`.`probation_month_done`, `vw_employee_current_appointment_info`.`seniority_date`, `vw_employee_current_appointment_info`.`represented`, `vw_employee_current_appointment_info`.`work_schedule`, `vw_employee_current_appointment_info`.`evaluation_end_date`, `vw_employee_current_appointment_info`.`evaluation_month_end`, `vw_employee_current_appointment_info`.`evaluation_sent_date`, `vw_employee_current_appointment_info`.`evaluation_completed`, `vw_employee_current_appointment_info`.`hiring_pi`, `vw_employee_current_appointment_info`.`appointment_type`, `vw_employee_current_appointment_info`.`appointment_type_code`, `vw_employee_current_appointment_info`.`appointment_classified`, `vw_employee_current_appointment_info`.`termination_type`, `vw_employee_current_appointment_info`.`head`, `vw_employee_current_appointment_info`.`secretary`, `vw_employee_current_appointment_info`.`division`, `vw_employee_current_appointment_info`.`supervisor_first_name`, `vw_employee_current_appointment_info`.`supervisor_last_name`, `vw_employee_current_appointment_info`.`title`, `vw_employee_current_appointment_info`.`title_code`, `vw_employee_current_appointment_info`.`udds`, `vw_employee_current_appointment_info`.`udds_code`,
`vw_employee_current_background_info`.`visa_holder`, `vw_employee_current_background_info`.`visa_type`, `vw_employee_current_background_info`.`visa_expiration_date`, `vw_employee_current_background_info`.`license`, `vw_employee_current_background_info`.`license_exp_date`, `vw_employee_current_background_info`.`dea`, `vw_employee_current_background_info`.`dea_expiration_date`, `vw_employee_current_background_info`.`national_provider_number`, `vw_employee_current_background_info`.`residency_location`, `vw_employee_current_background_info`.`residency_end_date`, `vw_employee_current_background_info`.`fellowship_location`, `vw_employee_current_background_info`.`fellowship_end_date`, `vw_employee_current_background_info`.`primary_board_cert`, `vw_employee_current_background_info`.`primary_cert_date`, `vw_employee_current_background_info`.`specialty_board_cert`, `vw_employee_current_background_info`.`specialty_cert_date`, `vw_employee_current_background_info`.`degree_info_reports`, `vw_employee_current_background_info`.`healthlink_id`, `vw_employee_current_background_info`.`uwmf_general_ledger_id`, `vw_employee_current_background_info`.`uwmf_employee_id`, `vw_employee_current_background_info`.`specialty`,
`vw_employee_current_compliance_info`.`hipaa_training_completed`, `vw_employee_current_compliance_info`.`sic_training_completed`, `vw_employee_current_compliance_info`.`background_check_completed`, `vw_employee_current_compliance_info`.`i9_completed`, `vw_employee_current_compliance_info`.`caregiver_applies`, `vw_employee_current_compliance_info`.`caregiver_check_completed`, `vw_employee_current_compliance_info`.`tb_completed`, `vw_employee_current_compliance_info`.`rubella_immunity_comfirmed`, `vw_employee_current_compliance_info`.`respiratory_test_completed`, `vw_employee_current_compliance_info`.`health_link`, `vw_employee_current_compliance_info`.`access_request_uwhc`, `vw_employee_current_compliance_info`.`rn_credentialing`, `vw_employee_current_compliance_info`.`bls_cert_expiration`, `vw_employee_current_compliance_info`.`uwhc_cred_submitted`,
 `vw_employee_current_contact_info`.`employee_id`, `vw_employee_current_contact_info`.`ext_office`, `vw_employee_current_contact_info`.`area_code_office`, `vw_employee_current_contact_info`.`number_office`, `vw_employee_current_contact_info`.`country_code_office`, `vw_employee_current_contact_info`.`ext_home`, `vw_employee_current_contact_info`.`area_code_home`, `vw_employee_current_contact_info`.`number_home`, `vw_employee_current_contact_info`.`country_code_home`, `vw_employee_current_contact_info`.`address1_office`, `vw_employee_current_contact_info`.`address2_office`, `vw_employee_current_contact_info`.`city_office`, `vw_employee_current_contact_info`.`state_office`, `vw_employee_current_contact_info`.`zip_office`, `vw_employee_current_contact_info`.`mail_code_office`, `vw_employee_current_contact_info`.`address1_home`, `vw_employee_current_contact_info`.`address2_home`, `vw_employee_current_contact_info`.`city_home`, `vw_employee_current_contact_info`.`state_home`, `vw_employee_current_contact_info`.`zip_home`, `vw_employee_current_contact_info`.`email`

from employee e
left join vw_employee_attributes_map on e.id = vw_employee_attributes_map.employee_id
left join vw_employee_current_appointment_info on e.id = vw_employee_current_appointment_info.employee_id
left join vw_employee_current_background_info on e.id = vw_employee_current_background_info.employee_id
left join vw_employee_current_compliance_info on e.id = vw_employee_current_compliance_info.employee_id
left join vw_employee_current_contact_info on e.id = vw_employee_current_contact_info.employee_id
where e.active = 1

而包含'division'和'udds'的vw_employee_current_appointment_info看起来像：

CREATE VIEW `vw_employee_current_appointment_info` AS

select e.id as `employee_id`, 

`appointment`.`termination_date`, `appointment`.`last_promotion_date`, `appointment`.`promotion_due_date`, `appointment`.`last_reappointment_date`, `appointment`.`reappointment_duration`, `appointment`.`reappointment_due_date`, `appointment`.`non_renewal_date`, `appointment`.`roster`, `appointment`.`payroll`, `appointment`.`on_probation`, `appointment`.`probation_complete`, `appointment`.`probation_notify_sent_date`, `appointment`.`probation_end_date`, `appointment`.`uw_appointment_id`, `appointment`.`effective_date`, `appointment`.`percent`, `appointment`.`end_date`, `appointment`.`continuity_status`, `appointment`.`guaranteed_length`, `appointment`.`end_reason`, `appointment`.`midterm_eval_received`, `appointment`.`final_eval_received`, `appointment`.`annual_eval_letter_sent`, `appointment`.`annual_eval_sent_date`, `appointment`.`annual_eval_received`, `appointment`.`annual_eval_received_date`, `appointment`.`probation_month_done`, `appointment`.`seniority_date`, `appointment`.`represented`, `appointment`.`work_schedule`, `appointment`.`evaluation_end_date`, `appointment`.`evaluation_month_end`, `appointment`.`evaluation_sent_date`, `appointment`.`evaluation_completed`, `appointment`.`hiring_pi`,
`appointment_type`.`name` as `appointment_type`, `appointment_type`.`code` as `appointment_type_code`, `appointment_type`.`classified` as `appointment_classified`,
`termination`.`name` as `termination_type`,
`appointment_division`.`head`, `appointment_division`.`secretary`,
`division`.`division_name` as `division`,
`supervisor`.`first_name` as `supervisor_first_name`, `supervisor`.`last_name` as `supervisor_last_name`, 
`title`.`name` as `title`, `title`.`code` as `title_code`,
`udds`.`name` as `udds`, `udds`.`code` as `udds_code`

from employee e 
left join appointment on appointment.employee_id = e.id and appointment.primary = 1
left join appointment_type on appointment.appointment_type_id = appointment_type.id
left join termination on appointment.termination_id = termination.id
left join appointment_division on appointment_division.appointment_id = appointment.id and appointment_division.primary = 1
left join division on appointment_division.division_id = division.id
left join appointment_supervisor on appointment_supervisor.appointment_id = appointment.id and appointment_supervisor.primary = 1
left join employee supervisor on appointment_supervisor.supervisor_id = supervisor.id
left join appointment_title on appointment_title.appointment_id = appointment.id and appointment_title.primary = 1
left join title on appointment_title.title_id = title.id
left join appointment_udds on appointment_udds.appointment_id = appointment.id and appointment_udds.primary = 1
left join udds on udds.id = appointment_udds.udds_id

Answer 1

您在表中使用了左连接。当连接条件为真时，选择所有表中匹配的记录而不是从左表中一一获取记录，在这种情况下，您的空条件为真并且重复结果集视图

Answer 2

您正在使用左连接，因此即使不存在任何值，您的基表也会连接到后续表。但是，当您开始过滤后续表时，您正在指定后续表包含某些值。在这种情况下，“vw_employee_current_appointment_info”中可能只有 319 个值，除法字段中为空。当您添加 udds 字段时，可能会有更多字段为空，因为左连接，除法字段根据定义为 NULL 因此，“vw_employee_current_appointment_info”的 udds 为 NULL 的连接数大于除法为 NULL 的记录数，因此它将它们全部带回来。如果您尝试使用相等的连接，则数量最多为 319。