Updating a values in mysql
Updating a values in mysql - Armenia sex chat
RE: Sadder But Wiser on February 8 2006 pmcreate table a (id int, v1 float, v2 float);insert into a values(1,1,2);update a SET v1=v1/(v1 v2), v2=v1/(v1 v2);select * from a; Actual Result:* 1 0.333333 0.142857Expected Result: 1 0.333333 0.333333This works exactly to the specifications of the documentation.5 | | -------- -------------------------------------------- Update column in a table whose values are not found in another table. The latter, however, swaps the values of column "name" in table tab1 with tab2.
This facilitates to update table1 column with expression whose corresponding value from table2 is returned as NULLupdate tab1, tab2 set tab1.name=tab2.name,tab2.name=tab1where tab1.id=tab2.idupdate tab2, tab1 set tab1.name=tab2.name,tab2.name=tab1where tab1.id=tab2The former leads to the values of column "name" in two tables are equal and equal to the original tab2
If you wish to use an increment based on subset of a table you may combine UPDATE with Variables:e.g.
A table that contains entries of different categories, in which an internal order needs to represented ( lets say a table with busstops on different routes).
If update (in two or more tables in ONE sql) many columns simultaneously by means of more complicated algorithm, eg., the value of one column is determined by other serval columns, things are worse.
I can not find the clear rule described as above, and have to write the sql in two sentances eventurally. As a preparation to sql store procedure, multi-table update can drastically accelerate the bulk update operation.
So, I do it in one "magick" query ;)Here an example:"3" is a some value, from form or somethingupdate item set rate = case when round((rate 3)/2) You sometimes run into the problem that you want to replace a substring occuring in a column with a different string, without touching the rest of the string.