如何使用join编写mysql查询，如果删除了一个表中的记录，仍会显示部分信息？

Question

i have a join query that displays info from 2 tables, but if a record is deleted from one of the tables, the joined record doesn't show. i still want to display the joined record but with the data from the first table showing and the info with the second table missing.

here is the query i'm working with.

$result = mysql_query("SELECT user_groups.*, pricing_groups.* FROM user_groups inner join pricing_groups on user_groups.pricing_group_id = pricing_groups.id LIMIT 2,18446744073709551615")

i'm limiting it by 2. i still want that in next version.

if record from pricing_groups is deleted that is attached to a record from user_groups, it's ok to show the user group info. in fact, i want it to display the user group info. but if it's the other way around...if a user group is deleted, then it's ok not to show either the user group info or pricing group info.

Answer 1

To include all records from user_groups you would need to use a LEFT JOIN like so:

SELECT ug.*, pg.* 
FROM user_groups AS ug
LEFT JOIN pricing_groups AS pg
ON ug.pricing_group_id = pg.id 
LIMIT 2,18446744073709551615

The LEFT JOIN returns all rows from the left table ( user_groups ), with the matching rows from the right table ( pricing_groups ). The result is NULL in the right side when there is no match.