I have a table (Table1) which has a composite primary key(Column1 + Column2). I am using it as a foreign key in another table (Table2).
Now I want to a SELECT statement to select all records from Table1 and Table2.
But its returning me 0 rows, because table2 is Empty. I want all records from table1 and if it does not exist in table2, value of Columns in Table2 should be null.
I know, I only need to Join it. But I am not getting it right.
Thanks
SELECT * FROM Table1 T1
LEFT JOIN Table2 T2 ON T1.Id = T2.FK
FK is your foreign key on the second table.
A Left Join will return all rows from table1 even if they don't exist in table2.
You need an outer join
SELECT *
FROM table1
LEFT OUTER JOIN table2
ON table1.column1 = table2.column1
AND table1.column2 = table2.column2
Left means preserve all rows from the left (first) table in the query.
You need a LEFT JOIN
SELECT Table1.*, Table2.*
FROM Table1
LEFT JOIN Table2 ON Table1.Column1 = Table2.Column2
Try that out.
Use LEFT JOIN for join you tables. See SQL SERVER JOINS to understand the concept.
Related
I have 2 tables
Lets say Table1 and Table2
They both have one shared value(id)
What I'm looking for is whether there is any function to combine them both based on that key, however if table2 has more elements, i want columns of table1 to be empty, and if table1 has more elements, table 2 columns to be empty
I tried a lot of different joins, but most of the time I end up with a lot of duplicate values as it tries to fill in both sides.
Tried Full outer join, Full join, etc
You are looking for full join:
select t1.*, t2.*
from t1 full join
t2
on t1.id = t2.id;
The above code from Gordon is right. However, since you have not specified the database and its version, I will post an alternate version for MySQL, which should also work for other databases.
Without duplicates:
SELECT * FROM Table1
LEFT JOIN Table2 ON Table1.id = Table2.id
UNION
SELECT * FROM Table1
RIGHT JOIN Table2 ON Table1.id = Table2.id
With duplicates:
SELECT * FROM Table1
LEFT JOIN Table2 ON Table1.id = Table2.id
UNION ALL
SELECT * FROM Table1
RIGHT JOIN Table2 ON Table1.id = Table2.id
I have three tables and I have to write one query to update table 1 row from table 3 and the only matching columns I have is in table 2.
Table 1 which has incorrect data:
Table 3 has the correct data:
I did try to write a query and execute it but it gives me an error saying there are too many rows too select which is true I do have many rows to correct but it still wouldn't correct. What do you think I should do. This is my query so far.
UPDATE Table1
SET Table1.Number = (SELECT Table3.Number
FROM Table2
FULL OUTER JOIN Table1 ON Table1.ID = Table2.ID
FULL OUTER JOIN Table3 ON Table3.Signin = Table2.Signin
WHERE (Table2.ID = Table1.ID)
AND (Table1.Number = 'xxx'))
WHERE (Tale1.Number = 'xxx')
In Where clause of JOIN query need to modify as multiple records are generating by inappropriate condition.Try to use Table3 components instead of using Table1 in joining query where clause.
UPDATE Table1
SET Table1.NUMBER = (SELECT table3.NUMBER FROM Table1 FULL OUTER JOIN Table2
ON Table1.ID = Table2.ID
FULL OUTER JOIN Table3
ON Table2.SIGNIN = Table3.SIGNIN
WHERE Table3.SIGNIN = 100) // This is the point where you need to modify your code
WHERE Table1.ID = 1;
ONLINE DEMO HERE
It actually worked after I removed this line from my query.
FULL OUTER JOIN Table1 ON table1.ID = Table2.ID
Thanks for the help.
You are fairly close. When doing the update though unless you are wanting to clear value for t1.number when a record is not matched in t3, you will want to use INNER JOIN. FULL OUTER JOIN would mean you are trying to update rows in t1 that don't exist but a LEFT JOIN you would update t1.number to NULL if a record in t3 doesn't exist.
UPDATE t1
SET t1.Number = t3.Number
FROM
Table1 t1
INNER JOIN Table2 t2
ON t1.Id = t2.Id
INNER JOIN Table3 t3
ON t2.Signin = t.3.Signin
WHERE
t1.number <> t3.number
--Or if you have nulls something like
--ISNULL(t1.number,'xxx') <> ISNULL(t3.number,'xxx')
-- if you only want to update when t1.number = 'xxx' then
--t1.number = 'xxx'
t1,t2,t3 are table aliases that I created by adding the alias after table name. By using join syntax rather than a sub select you simplify your were conditions. In sql-sever if more than 1 record in t2 & t3 match it will select one row randomly in the case of a one to many relationship. If you want a specific record when not one to one relation you can use window functions and common table expressions (cte) to limit t3 to the exact record you want to use.
Right now I have
SELECT
table1.field1 AS whatever
, table2.field2 AS stuff
FROM
table1
INNER JOIN table2 ON table1.goId = table2.Id
I need to be able to select a field3 which is located in a table3. Thing is, table1 has no direct foreign key pointing to table3, but it DOES have foreign key that points to a table which has another foreign key pointing to table3. How do I make the join between these 3 tables?
Given the lack of database structure provided the following could be used
SELECT
--Put column Declarations here--
table1.columnName1
,table2.columnName2
,table3.columnName3
FROM
table1
JOIN table2 ON table1.columnName1 = table2.columnName1
JOIN table4 ON table1.columnName1 = table4.columnName1
JOIN table3 ON table4.columnName4 = table3.columnName4
OR you could nest the third table
SELECT
--Put column Declarations here--
table1.columnName1
,table2.columnName2
,table3.columnName3
FROM
table1
JOIN table2 ON table1.columnName1 = table2.columnName1
JOIN table4
JOIN table3 ON table4.columnName4 = table3.columnName4
ON table1.columnName1 = table4.columnName1
Say that fourth table is table2.
SELECT
table3.column_You_want
FROM
table3
INNER JOIN table2 ON table2.column_linked_to_table3 = table3.column_name_linked_to_table2
INNER JOIN table1 ON table2.column_linked_to_table1 = table1.column_linked_to_table2
I have a mapping table referring to ids from two different tables. I would like to select the mapping table with each id being replaced by another field in the respective table.
To be a little more explicit: there are three tables with two columns each:
Table1 has a id (the primary key) and field1
Table2 has a id (the primary key) and field2
Table3 (the mapping table) has fields Table1_id (which takes values in Table1.id) and Table2_id (which takes values in Table2.id)
What I want is to get the content of Table3 with Table1.field1 and Table2.field2 as columns.
I know how to replace one of the columns in the mapping table with another column of one of the other tables, by using a inner join:
SELECT Table1.field1, Table3.Table2_id
FROM Table1
INNER JOIN Table3
ON Table1.id=Table3.Table1_id;
however I don't know how to do basically the same thing with both columns.
If i understood correctly you are trying to get field1 from Table1 and field2 from table 2. If so you just need to join the three tables
SELECT a.field1, c.field2
FROM Table1 a
INNER JOIN Table3 b
ON a.id=b.Table1_id
INNER JOIN Table2 c
ON b.Table2_id = c.id
Do another join.
SELECT Table1.field1, Table2.field
FROM Table1
INNER JOIN Table3
ON Table1.id = Table3.Table1_id
INNER JOIN Table 2
ON Table2.id = table3.table2_id;
You just need to join all three tables; something like
SELECT Table1.Field1, Table2.Field2
FROM Table3
JOIN Table1 ON Table1.Id = Table3.Table1_id
JOIN Table2 ON Table2.Id = Table3.Table2_id
I do not know if I understood correctly what you want to achieve but this should get you results from both tables joined by thier keys
SELECT Table1.field1, Table2.field2
FROM Table1
INNER JOIN Table3 ON Table1.id = Table3.Table1_id;
INNER JOIN Table2 ON Table2.id = Table3.Table2_id;
I have two tables Table1 and Table2. I compared thes tables using the query below. SELECT
Select Table1.ID
FROM Table1
LEFT OUTER JOIN Table2
ON Table1.ID =Table2.ID
WHERE Table2.ID IS NULL
and got 1508 records that exist in Table1 but not in Table2.
Now I wanted to delete these records in Table2. This is the code I used below
DELETE Table1.*
FROM Table1
LEFT OUTER JOIN Table2
ON Table1.ID =Table2.ID
WHERE Table2.ID IS NULL
This is the error I am get Could not delete from specified tables. I realize something is wrong with my sql, but where. I thought this DELETE was specifying a table not tables.
Try this:
DELETE FROM Table1
WHERE ID NOT IN
(
SELECT ID
FROM table2
)