I have this table that represents friendships
+--------+--------+
| user_1 | user_2 |
+--------+--------+
| 1 | 5 |
| 2 | 67 |
| 3 | 23 |
| ... | ... |
+--------+--------+
My goal is to create a procedure that returns friends of friends of a user (that does not include friends).
I started by creating a procedure to return friends for a given user
CREATE DEFINER=`user`#`localhost` PROCEDURE `getFriends`(IN `myuser` BIGINT(20))
NO SQL
BEGIN
DROP TABLE IF EXISTS friends;
CREATE TEMPORARY TABLE friends
SELECT user_2
FROM fb_friends
WHERE user_1=myuser;
END
This procedure, for user 534477793, creates the following temporary table
+------------+
| user_2 |
+------------+
| 527419864 |
| 580101923 |
| 620972114 |
| 651861323 |
| 662123645 |
| 676185145 |
| 682866129 |
| 718761310 |
| 729611272 |
| 1036862839 |
+------------+
Then I created another procedure that calls the first one and return friends of friends
CREATE DEFINER=`user`#`localhost` PROCEDURE `getFriendsOfFriends`(IN `myuser` BIGINT(20))
BEGIN
-- Creates the table friends
CALL getFriends(myuser);
SELECT DISTINCT(fb.user_2)
FROM fb_friends fb, friends f
-- This works
WHERE fb.user_1 IN (f.user_2)
-- This doesn't
AND fb.user_2 NOT IN (f.user_2);
END
And the query returns the following:
+------------+
| user_2 |
+------------+
| 729611272 |
| 527419864 |
| 651861323 |
| 676185145 |
| 1036862839 |
| 502741322 |
| 546744626 |
| 636845886 |
| 652813833 |
| 663713246 |
| 682866129 |
| 781419583 |
| 845134109 |
| 1355751897 |
| 1359286892 |
| 1275961636 |
| 620972114 |
| 509609160 |
| 662123645 |
| 1460283586 |
+------------+
So it's clear that the NOT IN didn't work since all values from getFriends are in the second results set.
I managed to get the results I wanted by doing ugly stuff but still, I'd like to understand what's wrong here. And there's no NULL value anywhere by the way.
Thanks!
That's because f.user_2 in your NOT IN is just a single user, not the entire set.
The correct way to do it is
SELECT DISTINCT(fb.user_2)
FROM fb_friends fb, friends f
WHERE fb.user_1 IN (f.user_2)
AND fb.user_2 NOT IN (SELECT * FROM friends);
Note the the first IN can be replaced with an = operator, because again there's only one element in the IN list.
Or you can completely remove the join to make the query consistent (but it will probably regress the performance)
SELECT DISTINCT(fb.user_2)
FROM fb_friends fb
WHERE fb.user_1 IN (SELECT * FROM friends)
AND fb.user_2 NOT IN (SELECT * FROM friends);
I thought the problem might be with temporary table and I was right. By executing the query in MySQLWorkbench the following error was ouput:
Error Code: 1137. Can't reopen table: 'friends'
So I went online to check if there was a limit on the number of times a temporary table can be used in the same query and in fact there is.
So I might just the temporary table into a permanent one (and drop it every time beforehand) and all will work as expected. sigh
Related
I am searching for all day with no success so I decided to ask.
I will very simplify structure as much as possible to ask for essence.
I have function:
mysql> SELECT set_of_ids_to_names('1:2:3:4:5', ':') AS `res`;
+-------------------------------+
| res |
+-------------------------------+
| NameA:NameB:NameC:NameD:NameE |
+-------------------------------+
I have table:
mysql> SELECT * FROM `tbl_tool`;
+----+-----------------+---------+
| ID | Tool | ID_name |
+----+-----------------+---------+
| 1 | Tool_1 | 1:2:3:4 |
| 2 | Tool_2 | 2:4:5 |
| 3 | Tool_3 | 4:5 |
| 4 | Tool_4 | 3 |
+----+-----------------+---------+
The result I would like to achieve is to have view called 'v_tool' so once I selet it I get:
mysql> SELECT * FROM `v_tool`;
+----+-----------------+-------------------------+
| ID | Tool | Name |
+----+-----------------+-------------------------+
| 1 | Tool_1 | NameA:NameB:NameC:NameD |
| 2 | Tool_2 | NameB:NameD:NameE |
| 3 | Tool_3 | NameD:NameE |
| 4 | Tool_4 | NameC |
+----+-----------------+-------------------------+
This what I tried is:
SELECT `tbl_tool`.`ID`, `tbl_tool`.`Tool`, `Name` FROM `tbl_tool`
INNER JOIN (SELECT set_of_ids_to_names((SELECT `ID` FROM `tbl_tool` WHERE `ID` = `tbl_tool`.`ID`), ':') AS `Name`) AS `aaa`
I know that it is wrong, but I just could not find idea how to pass proper value to function 'set_of_ids_to_names'.
Big thank you in advance.
Looking at the original function call you made:
SELECT set_of_ids_to_names('1:2:3:4:5', ':') AS `res`
It is important to note the function call appears in the SELECT clause, not in the FROM clause.
This suggests set_of_ids_to_names is a scalar function, not a table-valued function.
When querying table tbl_tool, you can do the exact same thing: call set_of_ids_to_names in the SELECT clause.
SELECT Tool, set_of_ids_to_names(ID_name, ':') AS Name
FROM tbl_tool
For table-valued functions, the situation is different of course. SQL Server has CROSS APPLY for that, in MySQL you'd probably have to join the table with a subquery encapsulating the function call.
I want to select value from table sorted by a certain order.
I have a table called test that looks like this:
| date | code | value |
+----------+-----------+----------+
| 20050104 | 000005.SZ | -6359.19 |
| 20050104 | 600601.SH | -7876.34 |
| 20050104 | 600602.SH | -25693.3 |
| 20050104 | 600651.SH | NULL |
| 20050104 | 600652.SH | -15309.9 |
...
| 20050105 | 000005.SZ | -4276.28 |
| 20050105 | 600601.SH | -3214.56 |
...
| 20170405 | 000005.SZ | 23978.13 |
| 20170405 | 600601.SH | 32212.54 |
Right now I want to select only one date, say date = 20050104, and then sort the data by a certain order (the order that each stock was listed in the stock market).
I have another table called stock_code which stores the correct order:
+---------+-----------+
| code_id | code |
+---------+-----------+
| 1 | 000002.SZ |
| 2 | 000004.SZ |
| 3 | 600656.SH |
| 4 | 600651.SH |
| 5 | 600652.SH |
| 6 | 600653.SH |
| 7 | 600654.SH |
| 8 | 600602.SH |
| 9 | 600601.SH |
| 10 | 000005.SZ |
...
I want to sorted the selected data by stock_code(code_id), but I don't want to use join because it takes too much time. Any thoughts?
I tried to use field but it gives me an error, please tell me how to correct it or give me an even better idea.
select * from test
where date = 20050104 and code in (select code from stock_code order by code)
order by field(code, (select code from stock_code order by code));
Error Code: 1242. Subquery returns more than 1 row
You told us that you don't want to join because it takes too much time, but the following join query is probably the best option here:
SELECT t.*
FROM test t
INNER JOIN stock_code sc
ON t.code = sc.code
WHERE t.date = '20050104'
ORDER BY sc.code_id
If this really runs slowly, then you should check to make sure you have indices setup on the appropriate columns. In this case, indices on the code columns from both tables as well as an index on test.date should be very helpful.
ALTER TABLE test ADD INDEX code_idx (code)
ALTER TABLE test ADD INDEX date_idx (date)
ALTER TABLE code ADD INDEX code_idx (code)
I'm currently working with a client that wants their database to duplicate info into a second table in a different format when it is initially inserted.
Basically like the following:
Table 1
| ID | NAME | EMAIL | password |
--------------------------------------
| 1 | david | x#x.co | asx234 |
| 2 | anthony | y#x.co | 24gss3 |
| 3 | jillian | z#x.co | hdfg5d |
Every time a row gets inserted into table 1 they also want to take that information from table 1 and add it to Table 2
Table 2
| ID | NAME | EMAIL | password | signature | level | lastenter | register_date |
-----------------------------------------------------------------------------------------------
| 1 | david | x#x.co | asx234 | text | 3 | 0000-00-00 | Date of insert |
| 2 | anthony | y#x.co | 24gss3 | text | 3 | 0000-00-00 | Date of insert |
| 3 | jillian | z#x.co | hdfg5d | text | 3 | 0000-00-00 | Date of insert |
How do I set up a trigger to insert the data into Table 2 whenever a row is inserted into table 1?
Thanks!
Some thoughts below, but the trigger would look something like this:
DELIMITER $$
DROP TRIGGER IF EXISTS trgMyNewTrigger $$
CREATE TRIGGER trgMyNewTrigger AFTER INSERT ON Table1
FOR EACH ROW
BEGIN
INSERT into Table2 (ID,NAME,EMAIL,`password`,signature,`level`,lastenter,register_date) VALUES (
new.ID, new.NAME, new.EMAIL, new.password, 'text', 3, '0000-00-00', CURDATE() );
END $$
DELIMITER ;
This is not a great solution. Triggers in general can cause some nasty issues and limit your capabilities down the road. It would be better to reconsider the design of the table to be inclusive of the data you need, have the application perform the extra step or use some sort of ETL process to get the data at set intervals.
I will all assume the clear text passwords are for the example.
I'm feeling a little rusty with creating queries in MySQL. I thought I could solve this, but I'm having no luck and searching around doesn't result in anything similar...
Basically, I have two tables. I want to select everything from one table and the matching row from the second table. However, I only want to have the first result from the second table. I hope that makes sense.
The rows in the daily_entries table are unique. There will be one row for each day, but maybe not everyday. The second table notes contains many rows, each of which are associated with ONE row from daily_entries.
Below are examples of my tables;
Table One
mysql> desc daily_entries;
+----------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------+--------------+------+-----+---------+----------------+
| eid | int(11) | NO | PRI | NULL | auto_increment |
| date | date | NO | | NULL | |
| location | varchar(100) | NO | | NULL | |
+----------+--------------+------+-----+---------+----------------+
Table Two
mysql> desc notes;
+---------+---------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+---------+---------+------+-----+---------+----------------+
| task_id | int(11) | NO | PRI | NULL | auto_increment |
| eid | int(11) | NO | MUL | NULL | |
| notes | text | YES | | NULL | |
+---------+---------+------+-----+---------+----------------+
What I need to do, is select all entries from notes, with only one result from daily_entries.
Below is an example of how I want it to look:
+----------------------------------------------+---------+------------+----------+-----+
| notes | task_id | date | location | eid |
+----------------------------------------------+---------+------------+----------+-----+
| Another note | 3 | 2014-01-02 | Home | 2 |
| Enter a note. | 1 | 2014-01-01 | Away | 1 |
| This is a test note. To see what happens. | 2 | | Away | 1 |
| Testing another note | 4 | | Away | 1 |
+----------------------------------------------+---------+------------+----------+-----+
4 rows in set (0.00 sec)
Below is the query that I currently have:
SELECT notes.notes, notes.task_id, daily_entries.date, daily_entries.location, daily_entries.eid
FROM daily_entries
LEFT JOIN notes ON daily_entries.eid=notes.eid
ORDER BY daily_entries.date DESC
Below is an example of how it looks with my query:
+----------------------------------------------+---------+------------+----------+-----+
| notes | task_id | date | location | eid |
+----------------------------------------------+---------+------------+----------+-----+
| Another note | 3 | 2014-01-02 | Home | 2 |
| Enter a note. | 1 | 2014-01-01 | Away | 1 |
| This is a test note. To see what happens. | 2 | 2014-01-01 | Away | 1 |
| Testing another note | 4 | 2014-01-01 | Away | 1 |
+----------------------------------------------+---------+------------+----------+-----+
4 rows in set (0.00 sec)
At first I thought I could simply GROUP BY daily_entries.date, however that returned only the first row of each matching set. Can this even be done? I would greatly appreciate any help someone can offer. Using Limit at the end of my query obviously limited it to the value that I specified, but applied it to everything which was to be expected.
Basically, there's nothing wrong with your query. I believe it is exactly what you need because it is returning the data you want. You can not look at as if it is duplicating your daily_entries you should be looking at it as if it is return all notes with its associated daily_entry.
Of course, you can achieve what you described in your question (there's an answer already that solve this issue) but think twice before you do it because such nested queries will only add a lot of noticeable performance overhead to your database server.
I'd recommend to keep your query as simple as possible with one single LEFT JOIN (which is all you need) and then let consuming applications manipulate the data and present it the way they need to.
Use mysql's non-standard group by functionality:
SELECT n.notes, n.task_id, de.date, de.location, de.eid
FROM notes n
LEFT JOIN (select * from
(select * from daily_entries ORDER BY date DESC) x
group by eid) de ON de.eid = n.eid
You need to do these queries with explicit filtering for the last row. This example uses a join to do this:
SELECT n.notes, n.task_id, de.date, de.location, de.eid
FROM daily_entries de LEFT JOIN
notes n
ON de.eid = n.eid LEFT JOIN
(select n.eid, min(task_id) as min_task_id
from notes n
group by n.eid
) nmin
on n.task_id = nmin.min_task_id
ORDER BY de.date DESC;
A previous DBA managed a non relational table with 2.4M entries, all with unique ID's. However, there are duplicate records with different data in each record for example:
+---------+---------+--------------+----------------------+-------------+
| id | Name | Address | Phone | Email | LastVisited |
+---------+---------+--------------+---------+------------+-------------+
| 1 | bob | 12 Some Road | 02456 | | |
| 2 | bobby | | 02456 | bob#domain | |
| 3 | bob | 12 Some Rd | 02456 | | 2010-07-13 |
| 4 | sir bob | | 02456 | | |
| 5 | bob | 12SomeRoad | 02456 | | |
| 6 | mr bob | | 02456 | | |
| 7 | robert | | 02456 | | |
+---------+---------+--------------+---------+------------+-------------+
This isnt the exact table - the real table has 32 columns - this is just to illustrate
I know how to identify the duplicates, in this case i'm using the phone number. I've extracted the duplicates into a seperate table - there's 730k entires in total.
What would be the most efficient way of merging these records (and flagging the un-needed records for deletion)?
I've looked at using UPDATE with INNER JOIN's, but there are several WHERE clauses needed, because i want to update the first record with data from subsequent records, where that subsequent record has additional data the former record does not.
I've looked at third party software such as Fuzzy Dups, but i'd like a pure MySQL option if possible
The end goal then is that i'd be left with something like:
+---------+---------+--------------+----------------------+-------------+
| id | Name | Address | Phone | Email | LastVisited |
+---------+---------+--------------+---------+------------+-------------+
| 1 | bob | 12 Some Road | 02456 | bob#domain | 2010-07-13 |
+---------+---------+--------------+---------+------------+-------------+
Should i be looking at looping in a stored procedure / function or is there some real easy thing i've missed?
U have to create a PROCEDURE, but before that
create ur own temp_table like :
Insert into temp_table(column1, column2,....) values (select column1, column2... from myTable GROUP BY phoneNumber)
U have to create the above mentioned physical table so that u can run a cursor on it.
create PROCEDURE myPROC
{
create a cursor on temp::
fetch the phoneNumber and id of the current row from the temp_table to the local variable(L_id, L_phoneNum).
And here too u need to create a new similar_tempTable which will contain the values as
Insert into similar_tempTable(column1, column2,....) values (Select column1, column2,.... from myTable where phoneNumber=L_phoneNumber)
The next step is to extract the values of each column u want from similar_tempTable and update into the the row of myTable where id=L_id and delete the rest duplicate rows from myTable.
And one more thing, truncate the similar_tempTable after every iteration of the cursor...
Hope this will help u...