Create data :
CREATE TABLE sub1(id int,name nvarchar(7));
CREATE TABLE sub2(id int,name nvarchar(7));
INSERT INTO sub1 VALUES(1,'one1');
INSERT INTO sub2 VALUES(1,'one1');
INSERT INTO sub1 VALUES(2,'one2');
INSERT INTO sub2 VALUES(2,'one2');
INSERT INTO sub1 VALUES(3,'one3');
INSERT INTO sub2 VALUES(4,'one4');
INSERT INTO sub1 VALUES(5,'one5');
INSERT INTO sub2 VALUES(6,'one6');
INSERT INTO sub1 VALUES(NULL,NULL);
INSERT INTO sub2 VALUES(NULL,NULL);
What's different between these 2 queries:
SELECT * FROM sub1 INTERSECT SELECT * FROM sub2;
SELECT sub1.id,sub1.name FROM sub1 JOIN sub2 ON sub1.id = sub2.id;
What's different between INTERSECT and JOIN?
INTERSECT just compares 2 sets and picks only distinct equivalent values from both sets. It's important to note that NULL marks are considered as equals in INTERSECT set operator. Also sets should contain equal number of columns with implicitly convertible types.
Under Join i guess you mean INNER JOIN?
INNER JOIN will return you rows where matching predicate will return TRUE. I.E. if there are NULL marks in both tables those rows will not be returned because NULL <> NULL in SQL.
Also INTERSECT is just comparing SETS on all attributes. Their types should be implicitly convertible to each other. While in join you can compare on any predicate and different types of sets. It is not mandatory to return just rows where there are matches. For example you can produce cartesian product in join.
Select * from Table1
Join Table2 on 1 = 1
Related
This question already has an answer here:
What's different between INTERSECT and JOIN?
(1 answer)
Closed 4 years ago.
I understand, that INNER JOIN is made for referenced keys and INTERSECT is not. But afaik in some cases, both of them can do the same thing. So, is there a difference (in performance or anything) between the following two expressions? And if there is, which one is better?
Expression 1:
SELECT id FROM customers
INNER JOIN orders ON customers.id = orders.customerID;
Expression 2:
SELECT id FROM customers
INTERSECT
SELECT customerID FROM orders
They are very different, even in your case.
The INNER JOIN will return duplicates, if id is duplicated in either table. INTERSECT removes duplicates. The INNER JOIN will never return NULL, but INTERSECT will return NULL.
The two are very different; INNER JOIN is an operator that generally matches on a limited set of columns and can return zero rows or more rows from either table. INTERSECT is a set-based operator that compares complete rows between two sets and can never return more rows than in the smaller table.
Try the following, for example:
CREATE TABLE #a (id INT)
CREATE TABLE #b (id INT)
INSERT INTO #a VALUES (1), (NULL), (2)
INSERT INTO #b VALUES (1), (NULL), (3), (1)
SELECT a.id FROM #a a
INNER JOIN #b b ON a.id = b.id
SELECT id FROM #a
INTERSECT
SELECT id FROM #b
Two different queries, produce two different result set.
Query 1:
Select a.customer_name, b.salary, c.manager_name
from
table123 a
left join table456 b on a.id=b.id
left join table789 c on a.id=c.id
Query2:
Select d.prty_id, e.party_val, f.prty_nme
from
table111 d
Left join table222 e on d.id=e.id
Left join table333 f on d.id=f.id
Now I have to write one single query, which will merge this above two query's result set and display one single result set.
Can anyone please help me on this.
Output value I need to insert in a new table whose column will be like below:
customer_name salary manager_name prty_id party_val prty_nme
According to your expected result, you can use UNION or UNION ALL.
The Oracle UNION operator is used to combine the result sets of 2 or more Oracle SELECT statements. It removes duplicate rows between the various SELECT statements.
The Oracle UNION ALL operator is used to combine the result sets of 2 or more SELECT statements. It returns all rows from the query and it does not remove duplicate rows between the various SELECT statements.
Select con1,... , coln
from tab1
where...
union
Select con1,... , coln
from tab2
where...
Just make sure your data types match up.
I have two tables -> tb1 and tb2.
I am performing left join operation on these tables using ID column and also i have one more condition such as one column is not equal to other column .
Below is sample code
select * from tb1 LEFT JOIN tb2 ON tb1.id=tb2.id AND tb1.pid!=tb2.pid;
I am able to get results from above query.
But i need to know is there any alternate ways to get same result using sql.?
The actually SQL standard uses <> instead of !=.
select * from tb1 LEFT JOIN tb2 ON tb1.id=tb2.id AND tb1.pid<>tb2.pid;
It seems to you not equal not working because of your join and join condition.
if we create two tables and create like your query
create table t1(id int,pid int);
create table t2 (id int,pid int );
insert into t1 values(1,2),(2,3),(3,4);
insert into t2 values(1,2),(2,3),(3,4);
select t1.* from t1 left join
t2 on t1.id=t2.id and
t1.pid!=t2.pid
order by t1.id
id pid
1 2
2 3
3 4
It returns all the values of 1st table, because LEFT JOIN returns all records from the left table (table1), and the matched records from the right table (table2). The result is NULL from the right side, if there is no match.
But if you put inner join in the same it will not return any row. so i think problem is not in the "not equal operator"
This question already has an answer here:
What's different between INTERSECT and JOIN?
(1 answer)
Closed 4 years ago.
I understand, that INNER JOIN is made for referenced keys and INTERSECT is not. But afaik in some cases, both of them can do the same thing. So, is there a difference (in performance or anything) between the following two expressions? And if there is, which one is better?
Expression 1:
SELECT id FROM customers
INNER JOIN orders ON customers.id = orders.customerID;
Expression 2:
SELECT id FROM customers
INTERSECT
SELECT customerID FROM orders
They are very different, even in your case.
The INNER JOIN will return duplicates, if id is duplicated in either table. INTERSECT removes duplicates. The INNER JOIN will never return NULL, but INTERSECT will return NULL.
The two are very different; INNER JOIN is an operator that generally matches on a limited set of columns and can return zero rows or more rows from either table. INTERSECT is a set-based operator that compares complete rows between two sets and can never return more rows than in the smaller table.
Try the following, for example:
CREATE TABLE #a (id INT)
CREATE TABLE #b (id INT)
INSERT INTO #a VALUES (1), (NULL), (2)
INSERT INTO #b VALUES (1), (NULL), (3), (1)
SELECT a.id FROM #a a
INNER JOIN #b b ON a.id = b.id
SELECT id FROM #a
INTERSECT
SELECT id FROM #b
I always thought of a Join in SQL as some kind of linkage between two tables.
For example,
select e.name, d.name from employees e, departments d
where employees.deptID = departments.deptID
In this case, it is linking two tables, to show each employee with a department name instead of a department ID. And kind of like a "linkage" or "Union" sideway".
But, after learning about inner join vs outer join, it shows that a Join (Inner join) is actually an intersection.
For example, when one table has the ID 1, 2, 7, 8, while another table has the ID 7 and 8 only, the way we get the intersection is:
select * from t1, t2 where t1.ID = t2.ID
to get the two records of "7 and 8". So it is actually an intersection.
So we have the "Intersection" of 2 tables. Compare this with the "Union" operation on 2 tables. Can a Join be thought of as an "Intersection"? But what about the "linking" or "sideway union" aspect of it?
You're on the right track; the rows returned by an INNER JOIN are those that satisfy the join conditions. But this is like an intersection only because you're using equality in your join condition, applied to columns from each table.
Also be aware that INTERSECTION is already an SQL operation and it has another meaning -- and it's not the same as JOIN.
An SQL JOIN can produce a new type of row, which has all the columns from both joined tables. For example: col4, col5, and col6 don't exist in table A, but they do exist in the result of a join with table B:
SELECT a.col1, a.col2, a.col3, b.col4, b.col5, b.col6
FROM A INNER JOIN B ON a.col2=b.col5;
An SQL INTERSECTION returns rows that are common to two separate tables, which must already have the same columns.
SELECT col1, col2, col3 FROM A
INTERSECT
SELECT col1, col2, col3 FROM B;
This happens to produce the same result as the following join:
SELECT a.col1, a.col2, a.col3
FROM A INNER JOIN B ON a.col1=b.col1 AND a.col2=b.col2 AND a.col3=b.col3;
Not every brand of database supports the INTERSECTION operator.
A join 'links' or erm... joins the rows from two tables. I think that's what you mean by 'sideways union' although I personally think that is a terrible way to phrase it. But there are different types of joins that do slightly different things:
An inner join is indeed an intersection.
A full outer join is a union.
This page on Jeff Atwood's blog describes other possibilities.
An Outer Join - is not related to - Union or Union All.
For example, a 'null' would not occur as a result of Union or Union All operation, but it results from an Outer Join.
INNER JOIN treats two NULLs as two different values. So, if you join based on a nullable column, and if both tables have NULL values in that column, then INNER JOIN will ignore those rows.
Therefore, to correctly retrieve all common rows between two tables, INTERSECT should be used. INTERSECT treats two NULLs as the same value.
Example(SQLite):
Create two tables with nullable columns:
CREATE TABLE Table1 (id INT, firstName TEXT);
CREATE TABLE Table2 (id INT, firstName TEXT);
Insert NULL values:
INSERT INTO Table1 VALUES (1, NULL);
INSERT INTO Table2 VALUES (1, NULL);
Retrieve common rows using INNER JOIN (This shows no output):
SELECT * FROM Table1 INNER JOIN Table2 ON
Table1.id=Table2.id AND Table1.firstName=Table2.firstName;
Retrieve common rows using INTERSECT (This correctly shows the common row):
SELECT * FROM Table1 INTERSECT SELECT * FROM Table2;
Conclusion:
Even though, many times both INTERSECT and INNER JOIN can be used to get the same results, they are not the same and should be picked depending on the situation.