MySQL cross-table update has always been the topic of concern, this article describes the MySQL Multi-table update in the practice of several different ways of writing, the need for a friend can refer to the assumption that we have two tables, a table for the Product table storage products information, including product price list The other table is the Productprice table, which 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:
UPDATE product P, Productprice pp
SET pp.price = Pp.price * 0.8
WHERE P.productid = Pp.productid
and p.datecreated < ' 2004-01-01 '
Another way is to use inner join and then update:
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 '
Alternatively, we can use the left outer join to do a multi-table update, for example, if there is no product price record in the Productprice table, set the IsDeleted field of the product table to 1, the following SQL statement:
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 the two tables, but only update the records in a table, in fact, you can update both tables, the following SQL:
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.
MySQL multi-table update SQL statement Summary
