I'm querying a table from a third party plugin so I don't have control over how the data is being inputted. It's a course plugin broken into 4 different quizzes. One of the questions is being used in all four quizzes.
THERE IS NO "quiz_id" which is why I think they only way to query data is with some sort of if conditional. There IS a date field and a unique id field.
This is what my subquery looks like:
(SELECT y.post_content
FROM wp_posts AS y
WHERE 137 = y.post_author
AND y.post_title LIKE '%If you checked "Other" in "What are your organization’s primary goals related to hiring people with autism?", please explain%'
ORDER BY y.post_author ASC limit 1)
This works to query the answer (y.post_content) for the first quiz, but not for all 4 quizzes. Is there a conditional I can use for this? i.e. let's say i'm querying results for the 2nd quiz: if there are four answers, pick the 2nd one,if there are 3 answers pick the 2nd one, if there are 2 answers, pick the most recent one
Related
In the table above table 'sent' I use, among other things, two fields: 'opened' and emailnumber.
I'm looking for a mysql query that the people who opened email number 1 and/or email number 2 one or more times
So in the example it would be everyone, except Fred
I think it's simple, but I can't find the solution
SELECT name
FROM table
GROUP BY name
HAVING SUM(open > 0);
I have some booking data from a pair of views in MySQL. They match columns perfectly, and the main difference is a booking code that is placed in one of these rows.
The context is as follows: this is for calculating numbers for a sports camp. People are booked in, but can do extra activities.
View 1: All specialist bookings (say: a football class).
View 2: A general group.
Due to the old software, the booking process results in many people booking for the general group and then are upgraded to the old class. This is further complicated by some things elsewhere in the business.
To be clear - View 1 actually contains some (but are not exclusively all) people from within View 2. There's an intersection of the two groups. Obviously people can't be in two groups at once (there's only one of them!).
Finding all people who are in View 2 is of course easy... as is View 1. BUT, I need to produce a report which is basically:
"View 1" overwriting "View 2"... or put another way:
"View 1" [sort of] UNION "View 2"
However: I'm not sure the best way of doing this as there are added complications:
Each row is as approximately (with other stuff omitted) as follows:
User ID Timeslot Activity
1 A Football
1 A General
2 A General
3 A Football
As you can see, these rows all concern timeslot A:
- User 2 does general activities.
- User 3 does football.
- User 1 does football AND general.
AS these items are non unique, the above is a UNION (distinct), as there are no truly distinct rows.
The output I need is as follows:
User ID Timeslot Activity
1 A Football
2 A General
3 A Football
Here, Football has taken "precedence" over "general", and thus I get the picture of where people are at any time.
This UNION has a distinct clause on a number of fields, but ignores others.
So: does anyone know how to do what amounts to:
"add two tables together and overwrite one of them if it's the same timeslot"
Or something like a:
"selective distinct on UNION DISTINCT".
Cheers
Rick
Try this:
SELECT *
FROM
(SELECT *,
IF(Activity='General',1,0) AS order_column
FROM `Table1`
ORDER BY order_column) AS tmp
GROUP BY UserId
This will add an order_column to your original table that as value 1 if the Activity value is general; Doing this we can select this temporary table ordering by this column (ascending order) and all record with general activity comes after all others. After that we can simply select the result of this temporary table grouping by user id. The group by clouse without any aggregate function takes the first record that match.
EDIT:
If you don't to use group by without aggregate function this is an 'ugly' alternative:
SELECT UserId,
Timeslot,
SUBSTRING(MAX(CASE Activity WHEN "General" THEN "00General" WHEN "Football" THEN "01Football" ELSE Activity END) , 3)
FROM `Table1`
GROUP BY UserId,
Timeslot LIMIT 0 ,
30
Here we need to define each possible value for Activity.
I have a 1 to many relationship between people and notes about them. There can be 0 or more notes per person.
I need to bring all the notes together into a single field and since there are not going to be many people with notes and I plan to only bring in the first 3 notes per person I thought I could do this using at most 3 queries to gather all my information.
My problem is in geting the mySQL query together to get the first, second, etc note per person.
I have a query that lets me know how many notes each person has and I have that in my table. I tried something like
SELECT
f_note, f_person_id
FROM
t_person_table,
t_note_table
WHERE
t_person_table.f_number_of_notes > 0
AND t_person_table.f_person_id = t_note_table.f_person_id
GROUP BY
t_person_table.f_person_id
LIMIT 1 OFFSET 0
I had hoped to run this up to 3 times changing the OFFSET to 1 and then 2 but all I get is just one note coming back, not one note per person.
I hope this is clear, if not read on for an example:
I have 3 people in the table. One person (A) has 0 notes, one (B) with 1 and one (C) with 2.
First I would get the first note for person B and C and insert those into my person table note field.
Then I would get the second note for person C and add that to the note field in the person table.
In the end I would have notes for persons B and C where the note field for person C would be a concatination of their 2 notes.
Welcome to SO. The thing you're trying to do, selecting the three most recent items from a table for each person mentioned, is not easy in MySQL. But it is possible. See this question.
Select number of rows for each group where two column values makes one group
and, see my answer to it.
Select number of rows for each group where two column values makes one group
Once you have a query giving you the three rows, you can use GROUP_CONCAT() ... GROUP BY to aggregate the note fields.
You can get one note per person using a nested query like this:
SELECT
f_person_id,
(SELECT f_note
FROM t_note_table
WHERE t_person_table.f_person_id = t_note_table.f_person_id
LIMIT 1) AS note
FROM
t_person_table
WHERE
t_person_table.f_number_of_notes > 0
Note that tables in SQL are basically without a defined inherent order, so you should use some form or ORDER BY in the subquery. Otherwise, your results might be random, and repeated runs asking for different notes might unexpectedly return the same data.
If you only aim for a concatenation of notes in any case, then you can use the GROUP_CONCAT function to combine all notes into a single column.
My team working on a php/MySQL website for a school project. I have a table of users with typical information (ID,first name, last name, etc). I also have a table of questions with sample data like below. For this simplified example, all the answers to the questions are numerical.
Table Questions:
qid | questionText
1 | 'favorite number'
2 | 'gpa'
3 | 'number of years doing ...'
etc.
Users will have the ability fill out a form to answer any or all of these questions. Note: users are not required to answer all of the questions and the questions themselves are subject to change in the future.
The answer table looks like this:
Table Answers:
uid | qid | value
37 | 1 | 42
37 | 2 | 3.5
38 | 2 | 3.6
etc.
Now, I am working on the search page for the site. I would like the user to select what criteria they want to search on. I have something working, but I'm not sure it is efficient at all or if it will scale (not that these tables will ever be huge - like I said, it is a school project). For example, I might want to list all users whose favorite number is between 100 and 200 and whose GPA is above 2.0. Currently, I have a query builder that works (it creates a valid query that returns accurate results - as far as I can tell). A result of the query builder for this example would look like this:
SELECT u.ID, u.name (etc)
FROM User u
JOIN Answer a1 ON u.ID=a1.uid
JOIN Answer a2 ON u.ID=a2.uid
WHERE 1
AND (a1.qid=1 AND a1.value>100 AND a1.value<200)
AND (a2.qid=2 AND a2.value>2.0)
I add the WHERE 1 so that in the for loops, I can just add " AND (...)". I realize I could drop the '1' and just use implode(and,array) and add the where if array is not empty, but I figured this is equivalent. If not, I can change that easy enough.
As you can see, I add a JOIN for every criteria the searcher asks for. This also allows me to order by a1.value ASC, or a2.value, etc.
First question:
Is this table organization at least somewhat decent? We figured that since the number of questions is variable, and not every user answers every question, that something like this would be necessary.
Main question:
Is the query way too inefficient? I imagine that it is not ideal to join the same table to itself up to maybe a dozen or two times (if we end up putting that many questions in). I did some searching and found these two posts which seem to kind of touch on what I'm looking for:
Mutiple criteria in 1 query
This uses multiple nested (correct term?) queries in EXISTS
Search for products with multiple criteria
One of the comments by youssef azari mentions using 'query 1' UNION 'query 2'
Would either of these perform better/make more sense for what I'm trying to do?
Bonus question:
I left out above for simplicity's sake, but I actually have 3 tables (for number valued questions, booleans, and text)
The decision to have separate tables was because (as far as I could think of) it would either be that or have one big answers table with 3 value columns of different types, having 2 always empty.
This works with my current query builder - an example query would be
SELECT u.ID,...
FROM User u
JOIN AnswerBool b1 ON u.ID=b1.uid
JOIN AnswerNum n1 ON u.ID=n1.uid
JOIN AnswerText t1 ON u.ID=t1.uid
WHERE 1
AND (b1.qid=1 AND b1.value=true)
AND (n1.qid=16 AND n1.value<999)
AND (t1.qid=23 AND t1.value LIKE '...')
With that in mind, what is the best way to get my results?
One final piece of context:
I mentioned this is for a school project. While this is true, then eventual goal (it is an undergrad senior design project) is to have a department use our site for students creating teams for their senior design. For a rough estimate of size, every semester, the department would have somewhere around 200 or so students use our site to form teams. Obviously, when we're done, the department will (hopefully) check our site for security issues and other stuff they need to worry about (what with FERPA and all). We are trying to take into account all common security practices and scalablity concerns, but in the end, our code may be improved by others.
UPDATE
As per nnichols suggestion, I put in a decent amount of data and ran some tests on different queries. I put around 250 users in the table, and about 2000 answers in each of the 3 tables. I found the links provided very informative
(links removed because I can't hyperlink more than twice yet) Links are in nnichols' response
as well as this one that I found:
http://phpmaster.com/using-explain-to-write-better-mysql-queries/
I tried 3 different types of queries, and in the end, the one I proposed worked the best.
First: using EXISTS
SELECT u.ID,...
FROM User u WHERE 1
AND EXISTS
(SELECT * FROM AnswerNumber
WHERE uid=u.ID AND qid=# AND value>#) -- or any condition on value
AND EXISTS
(SELECT * FROM AnswerNumber
WHERE uid=u.ID AND qid=another # AND some_condition(value))
AND EXISTS
(SELECT * FROM AnswerText
...
I used 10 conditions on each of the 3 answer tables (resulting in 30 EXISTS)
Second: using IN - a very similar approach (maybe even exactly?) which yields the same results
SELECT u.ID,...
FROM User u WHERE 1
AND (u.ID) IN (SELECT uid FROM AnswerNumber WHERE qid=# AND ...)
...
again with 30 subqueries.
The third one I tried was the same as described above (using 30 JOINs)
The results of using EXPLAIN on the first two were as follows: (identical)
The primary query on table u had a type of ALL (bad, though users table is not huge) and rows searched was roughly twice the size of the user table (not sure why). Each other row in the output of EXPLAIN was a dependent query on the relevant answer table, with a type of eq_ref (good) using WHERE and key=PRIMARY KEY and only searching 1 row. Overall not bad.
For the query I suggested (JOINing):
The primary query was actually on whatever table you joined first (in my case AnswerBoolean) with type of ref (better than ALL). The number of rows searched was equal to the number of questions answered by anyone (as in 50 distinct questions have been answered by anyone) (which will be much less than the number of users). For each additional row in EXPLAIN output, it was a SIMPLE query with type eq_ref (good) using WHERE and key=PRIMARY KEY and only searching 1 row. Overall almost the same, but a smaller starting multiplier.
One final advantage to the JOIN method: it was the only one I could figure out how to order by various values (such as n1.value). Since the other two queries were using subqueries, I could not access the value of a specific subquery. Adding the order by clause did change the extra field in the first query to also have 'using temporary' (required, I believe, for order by's) and 'using filesort' (not sure how to avoid that). However, even with those slow-downs, the number of rows is still much less, and the other two (as far as I could get) cannot use order by.
You could answer most of these questions yourself with a suitably large test dataset and the use of EXPLAIN and/or the profiler.
Your INNER JOINs will almost certainly perform better than switching to EXISTS but again this is easy to test with a suitable test dataset and EXPLAIN.
This is for a homework assignment. I haven't copy-pasted the question below, I made an simpler version of it that focuses on the specific area where I'm stuck.
Let's say I have a table of two values: a person's name, and the place he had lunch yesterday. Assume everyone has lunch in pairs. How can I query the database to return all the pairs of people that had lunch together yesterday? Each pair must be only listed once.
I'm actually not even sure what the professor means by return them as pairs. I've sent him an email, but no reply yet. It seems like he wants me to write a query that returns a table with column 1 as person 1 and column 2 as person 2.
Any suggestions on how to go about this? Does it seem right to assume he wants them as separate columns?
So far, I basically have:
SELECT name, restaurant FROM lunches GROUP BY restaurant, name
which essentially just reorganizes the table so that the people who had lunch together are one after the other.
We have to assume there can be only one pair eating lunch in a given restaurant.
You can get a list of pairs either using self-join:
SELECT l1.name, l2.name FROM lunches l1
JOIN lunches l2
ON l1.restaurant = l2.restaurant AND l1.name < l2.name
or using GROUP BY:
SELECT GROUP_CONCAT(name) FROM lunches
GROUP BY restaurant
The first query will return pairs in two different columns, while the second in one column, using comma as separator (default for GROUP_CONCAT, you can change it to whatever you wish).
Also note that for the first query names in pairs will come in alphabetical order as we use < instead of <> to avoid listing each pair twice.