将select语句的值设置为变量并在更新查询mysql中使用

Question

What I'm trying to achieve is to update a column on the database based on the result of a select query in mysql.

For example:

SELECT id, value, t_stamp FROM table_name ORDER BY id DESC Limit 1

then the value of the SELECT statement say would be

id    value    t_stamp

1      apple    2013-01-01

2      dog      2013-01-01

so then the value of the SELECT would be from 2 right. but i want to get the value of the 'value' column and use that as a parameter for the UPDATE

UPDATE table_name SET newvalue = value_from_select

so then value of the newvalue would be dog.

How can I do this in Mysql?

Answer 1

Is this what you are looking for?

select id,@b:=value,t_stamp from table_name ORDER BY id DESC Limit 1;

UPDATE table_name SET value = @b where id=2;

you can use @var:= operator to store the retrieved data in a user defined variable which can later be substituted in an update query as shown above. You can also use SET @a = 0 or 0.0 or '' to define its type before retrieving data in order to avoid confusion.