Max Block :
There are two tables with one-to-one relationship, and it's a legal that the second table can have less rows than the first.
Here is a sql code with inserted data:
create table data(
data_id int primary key,
name text
);
create table data_extra(
extra_id int references data(data_id) primary key ,
extra text
);
insert into data values (1, 'n1');
insert into data values (2, 'n2');
insert into data values (3, 'n3');
insert into data_extra values (1, 'e1');
insert into data_extra values (2, 'e2');
select * from data left join data_extra on data_id = extra_id;
-- data_id | name | extra_id | extra
-- ---------+------+----------+-------
-- 1 | n1 | 1 | e1
-- 2 | n2 | 2 | e2
-- 3 | n3 | |
-- (3 rows)
I need to make a query for all data
+ data_extra
tables where extra!='e1'
Here is my try:
select * from data left join data_extra on data_id = extra_id
where extra != 'e1';
-- data_id | name | extra_id | extra
-- ---------+------+----------+-------
-- 2 | n2 | 2 | e2
-- (1 row)
The problem with this query, that it doesn't return data.name='n3' row, which doesn't have a related row in data_extra table.
How can I fix it, to get as result data.name=n2 and data.name=n3.
GMB :
You could do:
select *
from data d
left join data_extra de on d.data_id = de.extra_id
where de.extra_id is null or de.extra <> 'e1'
This removes rows that match and whose extra
is equal to 'e1'
, while retaining non-matching rows.
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