I have 3 tables that look like this:
Table1:
PersonSSN
NumberOfCars
Table2:
PersonSSN
NumberOfPhones
Table3:
PersonName
PersonSSN
Both Table 1 and Table2 have a foreign key reference to Table3 on PersonSSN.
I need to join these in such a way that I get:
PersonName NumberOfPhones NumberOfCars
Here are some conditions that apply to the join:
If a person has an entry in both Table1 and Table2 I see all 3 fields populated for him.
If a person has an entry in Table1 and not in Table2 he should still show up but with NumberOfPhones set to 0.
Likewise, if a person has an entry in Table2 and not in Table1 he should still show up but with NumberOfCars set to 0.
Can this be achieved in one query ? If yes what should the query be ?
This is a left outer join query:
select t3.name, coalesce(t1.NumberOfPhones, 0), coalesce(t2.NumberOfCars, 0)
from table3 t3 left outer join
table1 t1
on t3.ssn = t1.ssn left outer join
table2 t2
on t3.ssn = t2.ssn;
Related
SELECT Table1.Filter, Table1.Condition, Combined.Data FROM Table1
LEFT JOIN
(SELECT Key, Data FROM IF(Table1.Filter, Table2, Table3))) AS Combined
ON Table1.Condition = Combined.Key
I want to create a MySQL View that shows all columns of Table1, and a column from either Table2 or Table3 depending on the field on Table1.Filter.
One simple solution is to LEFT JOIN both Table2 and Table3, with NULL on the column that is not applicable. Is there a way to avoid creating 2 columns?
I cannot UNION Table2 and Table3 as they might contain the same Key.
The following should do what you want:
SELECT t1.Filter, t1.Condition,
COALESCE(t2.Data, t3.Data) as Data
FROM Table1 t1 LEFT JOIN
Table2 t2
ON t1.Filter AND t2.Key = t1.Condition LEFT JOIN
Table3 t3
ON (NOT t1.Filter) AND t3.key = t1.condition;
You cannot have conditionals choosing tables in the FROM. But, you can have conditions in the ON conditions.
So here is the thing, I have two tables:
table1 has columns intUsersID, varUsersName
table2 has columns intCouriers, intResponsible
intCouriers (have some numbers of intUsersID that are Couriers), and intResponsible (have some numbers of intUsersID that are Responsible)
In my query I must see User Names of Couriers and of the Responsible persons
something like that:
SELECT
table1.varUsersName 'Couriers',
table1.varUsersName 'Responsible'
FROM
table1
LEFT JOIN
table2 ON table2.intCouriers = table1.intUsersID
And then I need some how to subquery or join this "table1.varUsersName 'Responsible'", to get also 'Reponsible' persons. Please help me.
Should be this
SELECT table1.varUsersName 'Couriers', table2.varUsersName 'Responsible'
FROM table1
INNER JOIN table3 on table1.intUsersID = table3.intCouriers
INNER JOIN table1 as Table2 on table2.intUsersID = table3. intResponsible
SELECT Couriers.varUsersName as "Couriers",
Responsible.varUsersName as "Responsible"
FROM `table2` t2
LEFT JOIN table1 Couriers on Couriers.intUsersID = t2.intCouriers
LEFT JOIN table1 Responsible on Responsible.intUsersID = t2.intResponsible
I have 2 tables t1 and t2. Each have a customer ID column. What I am looking for is to join the 2 columns and SUBTRACT the duplicates.
My EG:
Table1 and Table2 with the IDs for each
I have tried a union query. The result I am left with is ID = 1,2,3,4,5,6,7,8,9,10. Where, what I'm after is subtracting 1-5 from Table2 and the result = 6,7,8,9,10.
I hope that makes sense and that someone is able to help. Sorry if this is a bit too simple compared to what you're all used to.
In SQL Server you can use the EXCEPT operator:
select ID
from Table2
except
select ID
from Table1
Mysql does not support it though. Using a an in clause or a left join would work in both servers:
--Using In clause
SELECT ID
FROM Table2
WHERE ID NOT IN
(
SELECT ID
FROM Table1
);
--Using join
SELECT Table2.ID
FROM Table2
left join Table1
on Table2.ID = Table1.ID
where Table1.ID is null
Use left outer join
select * from t1 left outer join t2 on t1.customerid = t2.customerid
I am having 2 different tables like table1 and table2 in that i have a common column customer_id and then i want to pick customer_loan from table1 and customer_name from table2 using the common column customer_id and join both and display in my page anyone help me
It is simple
SELECT table1.customer_loan,table2.customer_nam
FROM table1 INNER JOIN table2 ON (table1.customer_id =table2.customer_id)
try this
select table1.customer_loan,table2.customer_nam from table1 inner join table2 on table1.customer_id = table2.customer_id
You need a JOIN, like this:
SELECT table1.customer_loan, table2.customer_nam
FROM table1 JOIN table2
USING (customer_id)
I have a quick question on JOINS.
If I wanted to find how many items from table1 that are used in table2, would I use a INNER JOIN or LEFT JOIN (se below).
An INNER JOIN would show me where 'ID' is in both tables so should represent when ID from table1 is used in table2, but then listing all table2 where ID is the same as table1 ID (LEFT JOIN) should bring back the same?
But the results are different:
INNER JOIN brings back 252,222
LEFT JOIN brings back 258,637
PS: table2 is a child of table1, so table2 IDs can only be from table1 (table1 a list of products, table2 a list of selected products) so looking for all products from table1 that are seleted so in table2 (been selected)
SELECT DISTINCT
t1.name, t1.details
FROM
table1 AS t1
INNER JOIN
table2 AS t2 ON t1.id = t2.t1_id
SELECT DISTINCT
t1.name, t1.details
FROM
table1 AS t1
LEFT JOIN
table2 AS t2 ON t1.id = t2.t1_id
Which would br the correct SQL, I'm guessing INNER JOIN.
LEFT JOIN is not the same as INNER JOIN. With a LEFT JOIN, those rows are returned too, that are not present in the second table! If you want those records, that have their IDs in the second table too, use INNER JOIN.
An INNER JOIN would show me where 'ID' is in both tables so should represent when ID from table1 is used in table2, but then listing all table2 where ID is the same as table1 ID (LEFT JOIN) should bring back the same?
In this case, an INNER JOIN makes perfect sense as it would give records common to both table1 and table2.
table2 is a child of table1, so table2 IDs can only be from table1 (table1 a list of products, table2 a list of selected products) so looking for all products from table1 that are seleted so in table2 (been selected)
This requires you to enforce FOREIGN KEY constraint in TABLE2 that IDs can only be present after they are present in TABLE1. Once you do this, then it makes sense.
For left join if the result is not satisfied joined then the result is returned from table1 and table2 null of.
In the case of inner join will return only results that satisfy the condition.