Mysql – One record, multiple updates in one query (MySQL)

MySQL

I run into a problem for which I didn't find an answer anywhere: If I have a table in which one specific value(here amount) from multiple records can add into a target record(from the same table), can I do it in a single query? This query below works, just that it only works for the first match(?!).

UPDATE test AS t1
LEFT JOIN test AS t2 ON t1.target = t2.obj_id
SET t2.amount = t2.amount + t1.amount, t1.amount = 0
WHERE t1.amount > 0 AND strcmp(t1.target, "null") <> 0;

Best Answer

I might be missing something here, but maybe it only works for the first match because it sets t1.amount = 0, which means that record is excluded from a repeated invocation of the same command (whose WHERE clause requires t1.amount > 0)?

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Mysql – Help with a complicated MySQL Query inserting data using select from 2 tables

Okay its done, the cursor usage worked

here is the code m using

UPDATE player_list_items SET player_list_item_cellX = cell_X, player_list_item_cellY = cell_Y
             WHERE player_list_id IN (
                 SELECT player_list_id FROM (
                 SELECT player_list_id FROM player_list_items 
                 WHERE player_list_player_id = playerID AND player_list_list_id = @listID AND player_list_item_cellX IS NULL
                 ORDER BY player_list_id LIMIT 1
                 ) tmp
             );

please let me know if this solution is not a good one... as I found nothing besides this to update multiples rows with different values..

its in a loop against cursor that have all the map_details data needs to be put in this table

MySQL: Delete a record from all tables in one shot

The automated way of doing so is by defining foreign keys on your tables, with a DELETE CASCADE in your case. This way, a DELETE on the master table will propagate and delete matching rows from all derived tables.

You will have to use InnoDB tables for that.

I assume your tables do not have foreign keys at the moment, otherwise you wouldn't ask. In which case you may try using triggers, see this post for an example. Triggers are bad for performance, mind you.

Those who do not define foreign keys tend to work out all DELETEs in application code.

Best Answer

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Mysql – Help with a complicated MySQL Query inserting data using select from 2 tables

MySQL: Delete a record from all tables in one shot

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