Change value in child table if parent table record meets condition

Question

If i have a table

parent_table {ID,code}

2 colums. ID - primary key

childe_table {ID,parent_table_ID, Name}

3 columns. parent_table_id is foreign key

I'm trying to create query to do this:

if(parent_table.code == 'x'){
    child_table.Name == 'value'
}

I know that I should use joins to do this. Could someone show me an example?

i don't understand your question... – rdn87 Jan 08 '16 at 14:14 — rdn87, Jan 08 '16 at 14:14

score 2 · Accepted Answer · edited May 23 '17 at 12:32

2

Look at this answer. You need to do

 UPDATE childe_table ct 
   JOIN parent_table pt ON ct.parent_table_id = pt.id  
   SET ct.code="value"
   WHERE pt.code='x'

edited May 23 '17 at 12:32

Community

answered Jan 08 '16 at 14:20

score 0 · Answer 2 · answered Jan 08 '16 at 14:16

0

Try this

update childe_table c 
set c.Name="value" 
where (select p.code from parent_table p where p.id=c.parent_table_id)="x"

answered Jan 08 '16 at 14:16

Evgeny

This is a very inefficient way of doing an update across a join. Instead of doing the join in the update, you are doing it on an inner select statement that gets executed for every record in the child table. – Jan 08 '16 at 14:40

2 Answers2