I need to SELECT FROM a mysql database and the result can be 0 or more rows.
For a certain column and for every row I need to do an UPDATE statement on a different table using this column.
How can I achieve this in the most efficient way?
What you want to do sounds like an update with a join. Something like this:
update table2 t2 join
table1 t1
on t2.col = t1.col and t1.val = #val
set t2.col2 = 1;
Related
I am trying to update a column here. When I run select statement, it gives proper results. But I am not able to update. Here is the script that I am running....
update table1
set col1 = 0
where col1 = 1 and col2 not in (select col3 from table1);
MySQL does not allow subqueries to reference the table being updated. So, use a left join instead:
update table1 t1 left join
table1 tt1
on t1.col2 = tt1.col3
set col1 = 0
where t1.col1 = 1 and tt1.col3 is null;
I also strongly advise you not to use not in with subqueries. The not in doesn't usually do what you intend when any value in the subquery is NULL. Hence, it is just a bad practice to use something that sometimes does not do what you intend.
I have a pretty simple MySQL query to implement, but I can't figure out how...
I have two tables, T1 and T2.
What I need to do:
From T1, I retrieve an ID based on a CODE value:
SELECT id FROM T1 WHERE code = '$code';
Then I need to use this ID (so the value I just retrieved) to update a specific row in T2 (the name of the row will match the ID's value).
I was thinking about using either subqueries or user-defined variables, but no matter how I try it I can't get it done.
If you have any code snippet that can help me doing that, I would appreciate it as well!
EDIT
Just to clarify something: I don't know the name of the column that I need to update in T2, since that name will be the value I retrieve from T1.
So for example, if the ID I get from T1 is "03", it will update the column named "03" in T2.
EDIT 2
Here's a little schema of what I intend to achieve (hoping I make myself clearer, I'm sorry for the misunderstanding...)
UPDATE T2 SET COL = YOUR_VALUE
WHERE T2.ID = (SELECT id FROM T1 WHERE code = '$code')
UPDATE: If the sub query returns more than one row then you can use from IN operator
UPDATE T2 SET COL = YOUR_VALUE
WHERE T2.ID IN (SELECT id FROM T1 WHERE code = '$code')
Use an UPDATE with a JOIN:
UPDATE T2
CROSS JOIN T1
SET T2.`0` = IF(T1.id = 0, T1.someColumn, T2.`0`),
T2.`1` = IF(T1.id = 1, T1.someColumn, T2.`1`),
T2.`2` = IF(T1.id = 1, T1.someColumn, T2.`1`)
WHERE T1.code = '$code'
Replace someColumn with the column in T1 containing the value you want to put into T2.
you can update without using the subquery just using join
update t2
inner join t1 on t2.name = t1.id and t1.code ='$code'
set t2.my_col = 'my_value'
but you should not use var in your query you are at risk for sql injection take a look at you mysql driver for param_binding
UPDATE T2 SET COL = YOUR_VALUE WHERE EXISTS
(SELECT 1 FROM T1 WHERE T2.id=T2.id AND code = '$code')
You can update T2 with the next SQL if you expect at least one row from the inner query
UPDATE T2 SET COLUMN = VALUE
WHERE T2.ID IN (SELECT ID FROM T1 WHERE CODE = $code)
Otherwise, if from T1 you are sure you will get only 1 record
UPDATE T2 SET COLUMN = VALUE
WHERE T2.ID = (SELECT ID FROM T1 WHERE CODE = $code)
I have a query like this:
UPDATE t1
SET t1.col1 = ( SELECT col1 FROM t2 WHERE <some_complex_conditions> ),
t1.col2 = ( SELECT col2 FROM t2 WHERE <some_complex_conditions> )
WHERE id = :id;
As you see, I have to execute the same query twice, every time for one column. Also as I've mentioned, that SELECT query has some complex conditions which need lots of processing. Now I want to know, how can I handle the UPDATE statement to get the update those two columns by single SELECT statement?
Something like this:
SELECT col1, col2 FROM t2 WHERE <some_complex_conditions>
In other word, how can I use this ^ into the UPDATE statement?
see multi table syntax in manual and stackoverflow
It's possible to update joined table. I think that it should be possible to join select statement, but I'm not sure, but I think example below shows equivalent query:
UPDATE t1
LEFT JOIN t2
-- joining condition, there can be the part <some complex condition>
ON t1.id = t2.ref_id AND t2.col3 = 'whatever you want'
SET t1.col1 = t2.col1, t1.col2 = t2.col2
--additional condition like WHERE t2.col1 IS NOT NULL
I need to build a update query. My existing code looks like this.
update table1
set data_plan=(select d.data_plan from table1 m,table2 d
where m.msidn = d.msidn and m.data_plan!=d.data_plan);
table 1 has columns msisdn and data_plan, table 2 also has same columns. I want to update the table1 data_plan column depending on some condition which I get through select query. But when I run the code I get this error.
You can't specify target table 'msisdn1' for update in FROM clause
Try it this way
update table1 m join table2 d
on m.msidn = d.msidn
and m.data_plan != d.data_plan
set m.data_plan = d.data_plan
Try this ...
UPDATE table1 SET m.data_plan=d.data_plan
FROM table1 m
INNER JOIN table2 d ON m.msidn = d.msidn and m.data_plan!=d.data_plan
I have got two tables. I want to update MODEL in table2 when ITEM in table1 equals ITEM in table2.
Any Ideas?
In MySQL, you do it like this
UPDATE table1 t1
INNER JOIN table2 t2
ON t1.id = t2.id
SET t1.col1 = t2.col1,
t1.col2 = t2.col2
If I understand correctly, you just want to perform an UPDATE on table2 based on, presumably, foreign keys?
If that's right, this should work:
UPDATE
table2
JOIN table1
ON table1.ITEM = table2.ITEM
SET
MODEL = 'new value';
The table declaration in an UPDATE statement is the same as is specified in a SELECT statement - so you can use any type of JOIN that fits your table/data.
Docs for UPDATE, SELECT.
If you could add an actual query attempt, or something, that might be helpful. Can you try something like the following:
UPDATE table2 JOIN table1 ON table2.ITEM = table1.ITEM SET MODEL = ?