Using one single SQL query with a join:
How can I add entries from a second table only if there is a corresponding entry available?
project source
description | source source_id | value
---------------------------- --------------------------------
Project 1 | 1 1 | Additional Info 1
Project 2 | null
When I type
select project.description, source.value
from project, source
where project.source = source.source_id
and project.description = "Project 1";
As desired I receive
Project 1 | Additional Info 1
However when I replace Project 1 with Project 2 in the last line, I won't get a result, because project.source is null.
Is it possible to use a single SQL query which outputs something like this?
Project 2 | null
I´m looking for a query which covers both cases.
Any ideas?
You can use a LEFT JOIN on the project table to make sure that all projects appear in the result set even if they have no matching value in the source table. Projects from the project table which do not match will have NULL for their value.
SELECT project.description AS description, source.value AS value
FROM project LEFT JOIN source
ON project.source = source.source_id
Output:
+--------------+--------------------+
| description | value |
---------------+--------------------+
| Project 1 | Additional Info 1 |
| Project 2 | null |
+--------------+--------------------+
Try to use left join....
SELECT project.description, source.value FROM project LEFT JOIN source ON project.source = source.source_id;
Related
I have two columns displaying the same type of information but not necessarily the same data. Although some of the data overlaps each column may/may not contain information that will also include NULL values. Like so:
Company ID | Company Name | Company ID | Company Name
-----------+--------------+------------+-------------
1 | A | 1 | A
2 | B | NULL | NULL
NULL | NULL | 3 | C
I am trying to merge columns 1 and 2 to columns 3 and 4, respectively, so that I have two columns that look like this:
Company ID | Company Name
-----------+-------------
1 | A
2 | B
3 | C
Looking at similar stackoverflow questions, I have doubt this may be done easily. Is this possible? Please, let me know!
Anything helps.
As you don't seem to be around to answer questions for clarification right now, let's go ahead.
It seems, you do actually have the four columns in question in a single table - but than, there should be no duplicate column names. Once they are unique, the following should work:
UPDATE SomeTable
SET company_ID_1 = IFNULL(company_ID_1, company_ID_2)
, company_Name_1 = IFNULL(company_Name_1, company_Name_2)
WHERE
company_ID_1 IS NULL
OR
company_Name_1 IS NULL
;
If the presented is actually the output of a join, you could replace the same by:
SELECT
IFNULL(SomeTable1.company_ID, SomeTable2.company_ID) company_ID
, IFNULL(SomeTable1.company_Name, SomeTable2.company_Name) company_Name
FROM SomeTable1
LEFT JOIN SomeTable2
ON SomeTable1.company_ID = SomeTable2.company_ID
UNION ALL
SELECT
IFNULL(SomeTable1.company_ID, SomeTable2.company_ID) company_ID
, IFNULL(SomeTable1.company_Name, SomeTable2.company_Name) company_Name
FROM SomeTable1
RIGHT JOIN SomeTable2
ON SomeTable1.company_ID = SomeTable2.company_ID
WHERE SomeTable1.company_ID IS NULL
ORDER BY company_ID
;
See it in action: SQL Fiddle
Please comment, if and as this requires adjustment / further detail.
For some reason, I am unable to export a table of subscribers from my phpList (ver. 3.0.6) admin pages. I've searched on the web, and several others have had this problem but no workarounds have been posted. As a workaround, I would like to query the mySQL database directly to retrieve a similar table of subscribers. But I need help with the SQL command. Note that I don't want to export or backup the mySQL database, I want to query it in the same way that the "export subscribers" button is supposed to do in the phpList admin pages.
In brief, I have two tables to query. The first table, user contains an ID and email for every subscriber. For example:
id | email
1 | e1#gmail.com
2 | e2#gmail.com
The second table, user_attribute contains a userid, attributeid, and value. Note in the example below that userid 1 has values for all three possible attributes, while userid's 2 and 3 are either missing one or more of the three attributeid's, or have blank values for some.
userid | attributeid | value
1 | 1 | 1
1 | 2 | 4
1 | 3 | 6
2 | 1 | 3
2 | 3 |
3 | 1 | 4
I would like to execute a SQL statement that would produce a row of output for each id/email that would look like this (using id 3 as an example):
id | email | attribute1 | attribute2 | attribute3
3 | e3#gmail.com | 4 | "" | "" |
Can someone suggest SQL query language that could accomplish this task?
A related query I would like to run is to find all id/email that do not have a value for attribute3. In the example above, this would be id's 2 and 3. Note that id 3 does not even have a blank value for attributeid3, it is simply missing.
Any help would be appreciated.
John
I know this is a very old post, but I just had to do the same thing. Here's the query I used. Note that you'll need to modify the query based on the custom attributes you have setup. You can see I had name, city and state as shown in the AS clauses below. You'll need to map those to the attribute id. Also, the state has a table of state names that I linked to. I excluded blacklisted (unsubscribed), more than 2 bounces and unconfirmed users.
SELECT
users.email,
(SELECT value
FROM `phplist_user_user_attribute` attrs
WHERE
attrs.userid = users.id and
attributeid=1
) AS name,
(SELECT value
FROM `phplist_user_user_attribute` attrs
WHERE
attrs.userid = users.id and
attributeid=3
) AS city,
(SELECT st.name
FROM `phplist_user_user_attribute` attrs
LEFT JOIN `phplist_listattr_state` st
ON attrs.value = st.id
WHERE
attrs.userid = users.id and
attributeid=4
) AS state
FROM
`phplist_user_user` users
WHERE
users.blacklisted=0 and
users.bouncecount<3 and
users.confirmed=1
;
I hope someone finds this helpful.
Lookup table - unique row identity
The other lookup tables just do not make sense as from what I have seen giving a row an ID then putting that id in another table which also has a id then adding these id's to some more tables which may reference them and still creating a lookup tables with more id's (this is how all the examples I can find seem) What I have done is this :
product_item - table
------------------------------------------
id | title | supplier | price
1 | title11 | suuplier1 | price1
etc.
it then goes on to include more items (sure you get it)
product_feature - table
--------------------------
id | title | iskeyfeature
1 | feature1 | true
feature_desc - table
-----------------------------
id | title | desc
1 | desc1 | text description
product_lookup - table
item_id | feature_id | feature_desc
1 | 1 | 1
1 | 2 | 2
1 | 3 | 3
1 |64 | 15
(as these only need to be referenced in the lookup the id's can be multiples per item or multiple items per feature)
What I want to do without adding item_id to every feature row or description row is retrieve only the columns from the multiple tables where their id is referenced in the same row of the lookup table. I want to know if it is possible to select all the referenced columns from the lookup row if I only know the item_id eg. Item_id = 1 return all rows where item_id = 1 with the columns referenced in the same row. Every item can have multiple features and also every feature could be attached to multiple items , this will not matter if I can just get the pattern right in how to construct this query from a single known value.
Any assistance or just some direction will be greatly appreciated. I'm using phpmyadmin, and sure this will be easier with some php voodoo I am learning mysql from tutorials ect and would like to know how to do it with sql directly.
Having a NULL value in a column is not the major concern that would lead to this design - it's the problem with adding new attribute columns in the future, at which MySQL is disgracefully bad.
If you want to make a query that returns everything about an item in one row, you need to LEFT OUTER JOIN back to the product_lookup table for each feature_id. This is about every 10th mysql question on Stack Overflow, so you should be able to find tons of examples.
I have 2 sql tables
Table name: agents contains a records with a coloumn AgentID
Table named: vacancies is the one with the data ans is being dislayed.
Table named vacancies has vacancies.Agents which contains values simmilar to this
VacanyID Company position CTC Candidates Agents
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
FBVAC001 | HDFC | Branch Manager | 4.5 | FBCAN001,FBCAN002| Agent3,Agent4
FBVAC003 | TBNH | Branch Manager | 4.5 | FBCAN004,FBCAN005| Agent2,Agent4
FBVAC005 | MMNT | Branch Manager | 4.5 | FBCAN008,FBCAN006| Agent3
FBVAC008 | LCFC | Branch Manager | 4.5 | FBCAN009,FBCAN023| Agent3,Agent4
FBVAC008 | KOTC | Branch Manager | 4.5 | FBCAN009,FBCAN023| Agent5,Agent4
I want to run a query that will return only those records that contain the value that corresponds to agents.AgentID from table name agents. This is the query so far but all it returs are those records that do not have more than one value in vacancies.Agents
for example if the value being searched for is Agent3 it should return rows1,3 and 4 instead it only returns row 3.
SELECT
vacancies.VacancyID,
vacancies.Company,
vacancies.`Position`,
vacancies.CTC,
vacancies.Candidates,
vacancies.Agents
FROM vacancies
, agents
WHERE (FIND_IN_SET(vacancies.Agents,agents.AgentID) <> 0)
How can this be resolved?
I believe you have your parameters backwards in FIND_IN_SET. The set should come second
FIND_IN_SET(agents.AgentID, vacancies.Agents)
More Info: http://www.bitbybit.dk/carsten/blog/?p=162
Also, if you are wanting to see only a specific agent, you need to filter for that as well, otherwise you're getting every possible combination of agent and matching vacancies (hence the duplicate rows):
AND Agents.AgentID = 'Agent3'
Demo: http://www.sqlfiddle.com/#!2/b4dcb/3
SELECT
vacancies.VacancyID,
vacancies.Company,
vacancies.`Position`,
vacancies.CTC,
vacancies.Candidates,
vacancies.Agents
FROM vacancies,
agents
WHERE (select
agents.agentid,
vacancies.agentid
from agents
left join vacancies
on vacancies.agentid = agents.agentid)
and agents.agentid = 'Agent3'
How are URLs (fragments) stored in a relational database?
In the following URL fragment:
~/house/room/table
it lists all the information on a table, and perhaps some information about the table.
This fragment:
~/house
outputs: Street 13 and Room, Garage, Garden
~/house/room
outputs: My room and Chair, Table, Window
What does the Database schema looks like? What if I rename house to flat?
Possible solution
I was thinking that I could create a hash for the URL and store it along with parentID and information. If I rename some upper-level segment I would then need to update all the rows which contain the given segment.
Then I thought would store each segment along with information and its level:
SELECT FROM items WHERE key=house AND level=1 AND key=room AND level=2
How do I solve this problem if the URL can be arbitrarily deep?
check The Adjacency List Model and The Nested Set Model described in Joe Celko's Trees and Hierarchies in SQL for Smarties
you should find plenty information to this topic. one article is here
Update
The Nested Set Model is very good if you are looking for a task like 'Retrieving a Single Path'. What you have is 'Find the Immediate Subordinates of a Node'. Here the Adjacency List Model is better.
| id | p_id | name |
| 1 | null | root |
| 2 | 1 | nd1.1 |
| 3 | 2 | nd1.2 |
| 4 | 1 | nd2.1 |
SQL to get a row with name of a fragment and it's direct sub items.
SELECT
p.name,
GROUP_CONCAT(
c.name
SEPARATOR '/'
) AS subList
FROM _table p
INNER JOIN _table c
ON p.id = c.p_id
WHERE p.name = 'root'
P.S. prefer WHERE p.id = 1. Id is unique where as name can be ambiguous.
see MySQL GROUP CONCAT function for more syntax details.