Updating a row in sql using php
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(This is because the order in which the rows are updated determines which rows are ignored.) Such statements produce a warning in the error log when using statement-based mode and are written to the binary log using the row-based format when using mode.
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.
when a row of a subset is lost/deleted/moved away from it, the whole subset will need to be reordered.
I had a problem - a had to update a column "rate" but if the existince or new value is greater then 5 this "5" will be finally value in field.
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.
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.
If you want to return the value before you updated it without using a seperate select (which unless you lock the table could return a different value than is updated) then you can use a mysql variable like this:update some_table set col = col 1 where key = 'some_key_value' and @value := col The @value := col will always evaluate to true and will store the col value before the update in the @value variable. Additional information on My SQL correlated subqueries is at UPDATE can apparently be used to implement a semaphore (pardon my pseudocode):while TRUE The code above waits until the semaphore is "cleared" (value = 0) and then "sets" it (value = 1).
See Section 126.96.36.199, “Inno DB and FOREIGN KEY Constraints”. Records not matching the equijoin from table2 are marked with null.
You cannot update a table and select from the same table in a subquery. This facilitates to update table1 column with expression whose corresponding value from table2 is returned as NULL It took me a few minutes to figure this out, but the syntax for UPDATING ONE TABLE ONLY using a relationship between two tables in My SQL 4.0 is actually quite simple:update t1, t2 set t1.field = t2.value where t1= t2.that; It should be noted that even simple applications of UPDATE can conflict with the 'safe mode' setting of the mysql daemon.
So, here it is again.]A very server resources friendly method to update multiple rows in the same table is by using WHEN THEN (with a very important note).
UPDATE tbl_name SET fld2 = CASE fld1WHEN val1 THEN data1WHEN val2 THEN data2ELSE fld2 ENDThe note is: do not forget ELSE.
If you do not use it, all rows that are outside the range of your updated values will be set to blank!