Suppose we have two tables, a table that holds product information for the product table, which contains price list prices; Another table is the Productprice table, and we want to update the Price field in the Productprice table to 80% of the price field in the prices table.
In MySQL we have several means to do this, one is update table1 t1, table2 ts ... The way:
Copy Code code as follows:
UPDATE product P, Productprice pp
SET pp.price = Pp.price * 0.8
WHERE P.productid = Pp.productid
and p.datecreated < ' 2004-01-01 '
Another approach is to use the inner join and then update:
Copy Code code as follows:
UPDATE Product P
INNER JOIN Productprice pp
On p.productid = Pp.productid
SET pp.price = Pp.price * 0.8
WHERE p.datecreated < ' 2004-01-01 '
In addition, we can use the left outer join to do more table update, for example, if there is no product price record in the Productprice table, the isdeleted field of the product table is set to 1, the following SQL statement:
Copy Code code as follows:
UPDATE Product P
Left JOIN Productprice pp
On p.productid = Pp.productid
SET p.deleted = 1
WHERE Pp.productid is null
In addition, the above examples are related to two tables, but only update the records in one table, in fact, you can update two tables, the following SQL:
Copy Code code as follows:
UPDATE Product P
INNER JOIN Productprice pp
On p.productid = Pp.productid
SET pp.price = Pp.price * 0.8,
P.dateupdate = Curdate ()
WHERE p.datecreated < ' 2004-01-01 '
Two tables are associated, updating the Price field of the Productprice table and the Dateupdate two fields of the Product table field.
