SELECT
teacher_info.teacher_id,
tearcher_name,
teacher_number,
tearcher_type,
teacher_image,
teacher_gender,
teacher_birthday,
identity_number,
company,
technical_title,
technical_grade,
major_type_id,
major_id,
courses_offer,
phone,
email,
relative_material,
LEVEL,
country,
province,
city,
region
FROM
teacher_info,
teacher_region_info
WHERE
teacher_info.teacher_id = teacher_region_info.teacher_id
上面的语句会让teacher_region_info表中如果没有对应的teacher_id就使teacher_info的数据也不显示出来了,如何更改代码?
找到了答案:
SELECT
teacher_info.teacher_id,
tearcher_name,
teacher_region_info.city
FROM
teacher_info,
teacher_region_info
WHERE
teacher_info.teacher_id = teacher_region_info.teacher_id
UNION
SELECT
teacher_info.teacher_id,
tearcher_name,
teacher_region_info.city
FROM
teacher_info,
teacher_region_info
WHERE
teacher_info.teacher_id != NULL