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select version();
| version() |
|---|
| 8.0.27 |
create table U(id int , nm char(11));
create table P(u_id int, txt varchar(64));
insert into U(id,nm) values (-1,'Anonymus'), (1,'One'),(2,'Two'),
(3,'Three'),(4,'Four');
insert into P(u_id, txt) values (1,'ntrcn11'),(1,'lkjhlkj456'),(3,'lkjhlkj456'),
(33,'Comment23'),(44,'Qury12');
select * from U; select * from P;
| id | nm |
|---|---|
| -1 | Anonymus |
| 1 | One |
| 2 | Two |
| 3 | Three |
| 4 | Four |
| u_id | txt |
|---|---|
| 1 | ntrcn11 |
| 1 | lkjhlkj456 |
| 3 | lkjhlkj456 |
| 33 | Comment23 |
| 44 | Qury12 |
select IFNULL(u1.nm,u2.nm), p.txt
from P p
left join U u1 on p.u_id = u1.id
inner join U u2 on u2.id=-1
| IFNULL(u1.nm,u2.nm) | txt |
|---|---|
| One | ntrcn11 |
| One | lkjhlkj456 |
| Three | lkjhlkj456 |
| Anonymus | Comment23 |
| Anonymus | Qury12 |