Update and left outer join statements

Question

I have two tabels with a relation and I want to update a field in table A. Is it possible to combine update and join in the same query? I googled it but didnt find any working s

Answer 1

If what you need is UPDATE from SELECT statement you can do something like this:

UPDATE suppliers    
SET city = (SELECT customers.city FROM customers

WHERE customers.customer_name = suppliers.supplier_name)

Answer 2

Update t 
SET 
       t.Column1=100
FROM 
       myTableA t 
LEFT JOIN 
       myTableB t2 
ON 
       t2.ID=t.ID

Replace myTableA with your table name and replace Column1 with your column name.

After this simply LEFT JOIN to tableB. t in this case is just an alias for myTableA. t2 is an alias for your joined table, in my example that is myTableB. If you don't like using t or t2 use any alias name you prefer - it doesn't matter - I just happen to like using those.

Answer 3

The Left join in this query is pointless:

UPDATE md SET md.status = '3' 
FROM pd_mounting_details AS md 
LEFT OUTER JOIN pd_order_ecolid AS oe ON md.order_data = oe.id

It would update all rows of pd_mounting_details, whether or not a matching row exists in pd_order_ecolid. If you wanted to only update matching rows, it should be an inner join.

If you want to apply some condition based on the join occurring or not, you need to add a WHERE clause and/or a CASE expression in your SET clause.

Answer 4

In mysql the SET clause needs to come after the JOIN. Example:

UPDATE e
    LEFT JOIN a ON a.id = e.aid
    SET e.id = 2
    WHERE  
        e.type = 'user' AND
        a.country = 'US';

Answer 5

Just another example where the value of a column from table 1 is inserted into a column in table 2:

UPDATE  Address
SET     Phone1 = sp.Phone
FROM    Address ad LEFT JOIN Speaker sp
ON      sp.AddressID = ad.ID
WHERE   sp.Phone <> ''