For multiple-table updates, there is no guarantee that assignments are carried out in any particular order. COLUMN2 IS NULLAn outerjoin is performed based on the equijoin condition.
If you set a column to the value it currently has, My SQL notices this and does not update it. Records not matching the equijoin from table2 are marked with null.
when a row of a subset is lost/deleted/moved away from it, the whole subset will need to be reordered.
This can be done similarily : SET @pos=0; UPDATE busstops SET pos = ( SELECT @pos := @pos 1 ) WHERE route = 1 ORDER BY pos ASCChris H (chansel0049) I experienced a weird issue converting from 4 to 5.
What I'm doing here is copying the information I need from the row where job_id=1 to the row where job_id=6, on the same table.
Adam Boyle's commment above was just what I was trying to do, update one table based on a relationship between that table and another.
His example was:update t1,t2 set t1.field=t2.value where t1.this=t2.that; That strikes me as an elegant syntax.
Here is the closest I could come up with for doing that on Oracle:update t1 set t1.field=(select value from t2 where t1.this=t2.that) where t1in (select that from t2); That strikes me as convoluted by comparison.
This option takes a list of one or more partitions or subpartitions (or both).
If you add new entries or move stops from one route to another you will most likely want to increment the position of the busstop within this route.
That's how you can do ittable busstopsid | route | busstop | pos1 | 1 | A | 1 2 | 1 | B | 2 3 | 1 | C | 3 4 | 2 | C | 1 5 | 2 | D | 2 6 | 2 | A | 3 7 | 2 | E | 4 8 | 2 | F | 5 9 | 2 | G | 610 | 2 | H | 7Moving D, E, F, G To route 1 SET @pos=(SELECT max(t1.pos) FROM busstops t1 WHERE t1.route = 1 ); UPDATE busstops SET pos = ( SELECT @pos := @pos 1 ), route =1 WHERE id IN (5,7,8,9)I doubt this could be done otherwise since referencing the table you wish to update within the subquery creates circular references After DELETE or UPDATE i.e.
Suppose you have a table where each row is associated with a certain group (For example, orders are associated with the customers placing them) where each item WITHIN the group has a distinct number (For example, each person my have a sequence of competition results - each person, therefore, has a 1st, 2nd, 3rd... If you would like to renumber items within their group so that each has the same baseline (say 0), here is an example way to proceed: Create TEMPORARY Table Groups (Id INTEGER AUTO_INCREMENT PRIMARY KEY, Name VARCHAR(31), Group Id VARCHAR(31), Val Within Group INTEGER); INSERT INTO Groups VALUES (null, "Davy", "Boy", 2); INSERT INTO Groups VALUES (null, "Mary", "Girl", 2); INSERT INTO Groups VALUES (null, "Bill", "Boy", 5); INSERT INTO Groups VALUES (null, "Jill", "Girl", -3); INSERT INTO Groups VALUES (null, "Fred", "Boy", 3);# Find the lowest value for each group CREATE TEMPORARY TABLE Group Sum AS SELECT Group Id, MIN(Val Within Group) AS base Val FROM Groups GROUP BY Group Id;# create an index so my SQL can efficiently match ALTER TABLE Group Sum ADD UNIQUE (Group Id);# finally, make the baseline adjustment UPDATE Groups LEFT JOIN Group Sum USING (Group Id) SET Val Within Group=Val Within Group-base Val; SELECT * FROM Groups;# 1 Davy Boy 0# 2 Mary Girl 5# 3 Bill Boy 3# 4 Jill Girl 0# 5 Fred Boy 1#Each group ("Boy", "Girl") now has a (lowest) Val Within Group entry of 0.
Notes: That index addition is necessary because on larger tables my SQL would rather die than figure to (internally) index a single column join.(Bug #11758262, Bug #50439) See Section 126.96.36.199, “Determination of Safe and Unsafe Statements in Binary Logging”, for more information.