I am stuck in my liaison of my 3 tables.
I have a table which is candidates with 3 fields (id_candidate, name_candidate, firstname_candidate)
An other table nammed lessons with 5 fields (id_lesson, price_lesson, date_lesson, fk_candidate, fk_monitor)
I have a table which is monitors with 3 fields (id_monitor, name_monitor, firstname_monitor)
I can join 2 tables (candidates and lessons)
Here is the request
SELECT *
FROM lessons INNER JOIN
candidates
ON lessons.fk_candidate=candidates.id_candidate
ORDER BY id_candidate ASC
But my problem is that. I don't understand how to join 3 tables?
In fact, the name of monitor must appear on the table lessons.
I have tried that
SELECT *
FROM candidates id_candidate INNER JOIN
lessons id_lesson
ON lessons.fk_candidate = candidates.id_candidate INNER JOIN
monitors id_monitor
ON lessons.fk_monitor = monitors.id_monitor;
Presumably, something like this:
SELECT c.*, l.*, m.name_monitor -- list out the columns you want explicitly
FROM candidates c INNER JOIN
lessons l
ON l.fk_candidate = c.id_candidate INNER JOIN
monitors m
ON l.fk_monitor = m.id_monitor;
Notes:
Using table aliases is a good idea. I recommend abbreviations for the table name.
After you have defined the table alias, use them. Your on clauses still referred to the table name.
Explicitly list the columns that you want.
Related
I am trying to join two tables from a database; energyImport and sunAlt.
energyImport has three columns: timestamp_id, energy, duration.
sunAlt has two columns: timestamp_id, altitude
I am doing an inner join on these two tables using the SQL:
SELECT *
FROM energyImport
INNER JOIN sunAz ON sunAz.timestamp_id = energyImport.timestamp_id;
The output from this is:
timestamp_id,duration,energy,timestamp_id,altitude
1601769600,1800,81310,1601769600,0.0
1601771400,1800,78915,1601771400,0.0
1601773200,1800,78305,1601773200,0.0
The problem is that the timestamp_id column is repeated. How can I join these columns and only include the first timestamp_id?
Replace the * with
energyImport.timestamp_id,energyImport.duration, energyImport.energy,
sunAz.altitude
Either you specify the columns that you want in the results:
SELECT e.timestamp_id, e.duration, e.energy, s.altitude
FROM energyImport e INNER JOIN sunAz s
ON s.timestamp_id = e.timestamp_id;
Or, use NATURAL instead of INNER join, so that the join is based on the columns(s) with the same names of the 2 tables (if this fits your requirement), because NATURAL join returns only 1 of each pair of these columns:
SELECT *
FROM energyImport NATURAL JOIN sunAz;
See the demo.
I have the following DB structure:
And right now I can't make up a query to get
a creator data, admin data and tech data from item_contacts...
What kind of JOIN I need to use and how?
I think you want 3 joins on item_contacts - one for each column whose data you want to recover:
select
i.*,
cc.data as creator_data,
ca.data as admin_data,
ct.data as tech_data
from items i
inner join item_contacts cc on cc.contact_id = i.creator_id
inner join item_contacts ca on ca.contact_id = i.admin_id
inner join item_contacts ct on ct.contact_id = i.tech_id
I am attempting to access data from the following tables:
OrgPlanYear
ProjOrgPlnYrJunction
DC
DCMaxEEContribLevel
DCNonDiscretionaryContribLevel
Basically, I need to inner join OrgPlanYear + DC and ProjOrgPlnYrJunction then I need to Left Join the remaining tables (tables 4 and 5) due to the fact the tables 1-3 have all the rows I need and only some have data in tables 4-5. I need several variables from each table. I also need the WHERE function to be across all fields (meaning I want all this data for a select group where projectID=919).
Please help!
I have tried many things with errors including attempting to use the Design Query side (i.e. JOIN function issues, badly formatted FROM function, etc.)! Here is an example of one excluding all variables I need:
SELECT
ProjOrgPlnYrJunction.fkeyProjectID, OrgPlanYear.OrgName, DC.PlanCode, DCNonDiscretionaryContribLevel.Age,DCNonDiscretionaryContribLevel.Service
FROM
(((OrgPlanYear INNER JOIN DC ON OrgPlanYear.OrgPlanYearID = DC.fkeyOrgPlanYearID) INNER JOIN ProjOrgPlnYrJunction ON OrgPlanYear.OrgPlanYearID = ProjOrgPlnYrJunction.fkeyOrgPlanYearID)
LEFT JOIN
(SELECT DCNonDiscretionaryContribLevel.Age AS Age, DCNonDiscretionaryContribLevel.Service AS Service FROM DCNonDiscretionaryContribLevel WHERE ProjOrgPlnYrJunction.fkeyProjectID)=919)
LEFT JOIN (
SELECT DCMaxEEContribLevel.EEContribRoth FROM EEContribRoth WHERE ProjOrgPlnYrJunction.fkeyProjectID)=919)
ORDER BY OrgPlanYear.OrgName;
Main issues with your query:
Missing ON clauses for each LEFT JOIN.
Referencing other table columns in SELECT and WHERE of a different subquery (e.g., FROM DCNonDiscretionaryContribLevel WHERE ProjOrgPlnYrJunction.fkeyProjectID).
Unmatched parentheses around subqueries and joins per Access SQL requirements.
See below adjusted SQL that now uses short table aliases. Be sure to adjust SELECT and ON clauses with appropriate columns.
SELECT p.fkeyProjectID, o.OrgName, DC.PlanCode, dcn.Age, dcn.Service, e.EEContribRoth
FROM (((OrgPlanYear o
INNER JOIN DC
ON o.OrgPlanYearID = DC.fkeyOrgPlanYearID)
INNER JOIN ProjOrgPlnYrJunction p
ON o.OrgPlanYearID = p.fkeyOrgPlanYearID)
LEFT JOIN
(SELECT Age AS Age, Service AS Service
FROM DCNonDiscretionaryContribLevel
WHERE fkeyProjectID = 919) AS dcn
ON dcn.fkeyProjectID = p.fkeyOrgPlanYearID)
LEFT JOIN
(SELECT EEContribRoth
FROM EEContribRoth
WHERE fkeyProjectID = 919) AS e
ON e.fkeyProjectID = p.fkeyProjectID
ORDER BY o.OrgName;
I have two tables, one for all the foods which contains food id, default name and other foods values.
Another table is for the food name translations which contains food id, language id, translation.
What i want to do is join between these tables by the food id to get the translation for food id = 5 for example and language id = 1 which is Spanish for example. and i do it by:
SELECT *
FROM Foods
INNER JOIN FoodNameTranslations USING(Food_ID)
WHERE Food_ID = 5
AND Language_ID = 1
Now what if the the 'FoodNameTranslations' table doesn't have a translation for Food_ID 5 and Language 1?
then i want to simply get the food row with food id = 5 from the 'Foods' table (that contains the default name).
How can i make one query that does this? thanks!
You would do a LEFT JOIN and put the language ID into the join condition.
SELECT
COALESCE(t.TranslatedName, f.DefaultName) FoodName
FROM
Foods f
LEFT JOIN FoodNameTranslations t ON t.Food_ID = f.Food_ID AND t.Language_ID = 1
WHERE
f.Food_ID = 5
You cando do this by changing the JOIN condition:
INNER JOIN gets all records that are common between both tables based on the supplied ON clause.
LEFT JOIN gets all records from the LEFT linked and the related record from the right table ,but if you have selected some columns from the RIGHT table, if there is no related records, these columns will contain NULL.
RIGHT JOIN is like the above but gets all records in the RIGHT table.
FULL JOIN gets all records from both tables and puts NULL in the columns where related records do not exist in the opposite table.
Try using LEFT JOIN instead INNER JOIN, you query will be like this:
SELECT *
FROM Foods
LEFT JOIN FoodNameTranslations USING(Food_ID)
WHERE Food_ID = 5
AND Language_ID = 1
I want to retrieve data from 4 tables. Patient table has id as PK which is the foreign key in other three tables ett, phar and ssc. Where a patient lie in only one category. i.e patient id pt1 exists in either of the 3 tables. now I want to retrieve patient info along with its associated category.
My query is:
SELECT *
FROM Patient p
INNER JOIN ETT t
ON p.Patient_ID = t.Patient_ID || INNER JOIN Pharmacological ph
ON p.Patient_ID = ph.Patient_ID
I used OR clause because I want only 1 inner join executing at one time. but its not giving me results, any suggestions??
....Patient table has ID as PK which is the foreign key in other three
tables name: ett, phar and ssc where a patient lie in only one
category. Example, patient id pt1 exists in either of the 3 tables.
Based on your statement, you can join all the tables in table Patient using LEFT JOIN since a record can only exist on one table. The query below uses COALESCE which returns the first non-null value with int the list.
The only thing you need is to manually specify the column names that you want to be shown on the list as shown below.
SELECT a.*,
COALESCE(t.colA, p.ColA, s.ColA) ColA,
COALESCE(t.colB, p.ColB, s.ColB) ColB,
COALESCE(t.colN, p.ColN, s.ColN) ColN
FROM Patient a
LEFT JOIN ETT t
ON a.Patient_ID = t.Patient_ID
LEFT JOIN Phar p
ON a.Patient_ID = p.Patient_ID
LEFT JOIN SSC s
ON a.Patient_ID = s.Patient_ID
To further gain more knowledge about joins, kindly visit the link below:
Visual Representation of SQL Joins
For or - do not ise ||, use "or"
You cannot join with or, you need re-format your query.