This question already has answers here:
Condition within JOIN or WHERE
(10 answers)
Closed 9 years ago.
which example below is best practice for inner joins? the examples below are
pretty simple but, what if there are multiple tables involved?
which approach would you choose?
example queries:
simple
SELECT suppliers.supplier_id, suppliers.supplier_name, orders.order_date
FROM suppliers, orders
WHERE suppliers.supplier_id = orders.supplier_id;
using keyword INNER JOIN
SELECT suppliers.supplier_id, suppliers.supplier_name, orders.order_date
FROM suppliers
INNER JOIN orders
ON suppliers.supplier_id = orders.supplier_id;
Since 1992 ANSI recommends the JOIN notation, and regarding to readability this is what I would recommend using.
Everything has been said on this topic, but I will just remind that from a logical point of view it makes much more sense to separate the join conditions from the value filters for 2 reasons:
that's not the same thing at all
Oracle internally (and mysql probably too, even though I don't really know) first calculates intermediate recordsets and THEN, afterwards, applies the WHERE filters.
I'd recommend explicitly stating JOIN type and using ON clause.
But you need to use it correctly. In your example you forgot to include FROM clause and suppliers table.
SELECT suppliers.supplier_id,
suppliers.supplier_name,
orders.order_date
FROM suppliers s INNER JOIN
orders o ON s.supplier_id = o.supplier_id;
In terms of functionalities both WHERE AND JOINS are same..
Related
This question already has answers here:
INNER JOIN ON vs WHERE clause
(12 answers)
Closed 5 years ago.
Are the following two select SQL statements exactly equal? I usually use the join keyword, but I found that the sqlite author uses the second form in some of his document pages on sqlite.org.
The "inner join...on" form
SELECT * FROM Order INNER JOIN OrderItem ON Order.Id = OrderItem.ParentId
The "where" form
SELECT * FROM Order, OrderItem WHERE Order.Id = OrderItem.ParentId
Update 1:
I found this question might be duplicated, it seems has something to do with the SQL89 and SQL92 standards, but it doesn't answer me the second form is an "INNER JOIN", "OUTER JOIN" or anything else.
Result will be the same but there are separate purpose of each syntax.
for more details check this inner join vs where
If you talk about specifically the query you mentioned then yes both will result the same but join and where clause don't give same results. join is used for joining two tables and where clause is further used to specify the data selection from those tables.
This question already has answers here:
Explicit vs implicit SQL joins
(12 answers)
Closed 6 years ago.
I am currently learning SQL. I am trying to create Views using Oracle SQL Developer. I came across the JOIN statement but I do not understand why do we need JOIN. According to W3School, the purpose of JOIN is to join multiple rows together. I can do that without the expression JOIN (refer to the following code blocks, both of them produce the same view/table). So what is the purpose of JOIN?
With INNER JOIN:
SELECT
Acc.Cust_Id,
Cus.Address,
Acc.Avail_Balance
FROM
Account Acc
INNER JOIN
Customer Cus
ON
Acc.Cust_Id = Cus.CUST_ID
Without INNER JOIN:
SELECT
Acc.Cust_Id,
Cus.Address,
Acc.Avail_Balance
FROM
Account Acc,
Customer Cus
WHERE
Acc.Cust_Id = Cus.CUST_ID
The two queries are the same, except the 1st one ANSI-92 SQL syntax and the and other is older SQL syntax which didn't incorporate the join clause. They should produce exactly the same internal query plan, although you may like to check.
check This link
ANSI vs. non-ANSI SQL JOIN syntax
This question already has answers here:
INNER JOIN ON vs WHERE clause
(12 answers)
Closed 8 years ago.
Hello :) I've got a question on MySQL queries.
Which one's faster and why?
Is there any difference at all?
select tab1.something, tab2.smthelse
from tab1 inner join tab2 on tab1.pk=tab2.fk
WHERE tab2.somevalue = 'value'
Or this one:
select tab1.something, tab2.smthelse
from tab1 inner join tab2 on tab1.pk=tab2.fk
AND tab2.somevalue = 'value'
As Simon noted, the difference in performance should be negligible. The main concern would be ensuring your query correctly expresses your intent, and (especially) you get the expected results.
Generally, you want to add filters to the JOIN clause only if the filter is a condition of the join. In most (not all) cases, a filter should be applied to the WHERE clause, as it is a filter of the overall query, not of the join itself.
AFAIK, the only instance where this really affects the outcome of the query is when using an OUTER JOIN.
Consider the following queries:
SELECT *
FROM Customer c
LEFT JOIN Orders o ON c.CustomerId = o.CustomerId
WHERE o.OrderType = "InternetOrder"
vs.
SELECT *
FROM Customer c
LEFT JOIN Orders o ON c.CustomerId = o.CustomerId AND o.OrderType = "InternetOrder"
The first will return one row for each customer order that has an order type of "Internet Order". In effect, your left join has become an inner join because of the filter that was applied to the whole query (i.e. customers who do not have an "InternetOrder" will not be returned at all).
The second will return at least one row for each customer. If the customer has no orders of order type "Internet Order", it will return null values for all order table fields. Otherwise it will return one row for each customer order of type "Internet Order".
If the constraint is based off the joined table (as yours is) then it makes sense to specify the constraint when you join.
This way MySQL is able to reduce the rows from the joined table at the time it joins, as otherwise it will need to be able to select all data that fulfills the basic JOIN criteria prior to applying the WHERE logic.
In reality you'll see little difference in performance until you get to more complex queries or larger datasets, however limiting the data at each JOIN will be more efficient overall if done well especially if there are good indexes on the joined table.
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
SQL join: where clause vs. on clause
What are the difference between of following table joining ways
and which one is more appreciate for query optimization.
SELECT SP.*, S.SNAME, S.STATUS, S.CITY
FROM S INNER JOIN SP
ON S.SNO = SP.SNO;
and
SELECT SP.*, S.SNAME, S.STATUS, S.CITY
FROM S, SP
WHERE S.SNO = SP.SNO;
The query optimiser will treat them both as equivalent - there is no difference in performance on all the major database engines.
From a readability and stylistic point of view, using the explicit join syntax is usually preferred - whatever you do, settle on a convention and stick to it!
there is one point to remember here
the column on which index is defined should be the first in on clause make a little difference
This question already has answers here:
Closed 11 years ago.
Possible Duplicate:
INNER JOIN versus WHERE clause — any difference?
SQL JOIN: is there a difference between USING, ON or WHERE?
For example, I have this SQL statement:
SELECT *
FROM orders, inventory
WHERE orders.product = inventory.product
or
SELECT *
FROM orders
JOIN inventory
ON orders.product = inventory.product
What is the difference between these two?
They do exactly the same thing, but I'd recommend the second approach for readability and maintainability.
Using JOIN allows you to separate the conditions that define relationships between tables from conditions which are filters on the result set.
Using JOIN makes it easier to see if you are missing a join condition.
Using JOIN allows you to easily choose between INNER or OUTER JOIN. The comma syntax is equivalent to INNER JOIN (though some databases do have an extension to allow an outer join when using the first approach).
The most important is to be consistent about which you use. The comma syntax has different precedence from the JOIN keyword which can lead to confusing errors if you try to mix the two syntaxes in the same query. Because of point 3, it is easier to be consistent if you always use JOIN.
Inner join is ansi syntax, should be the preferred method.
Imagine how ugly this solution could get if you were to use the , with say many tables?
SELECT * FROM orders, inventory, products, logistics, accounting, materials, ...
Be kind to your future developers and anyone else looking at or maintaining this code use the JOIN syntax.
The comma (,) is equivalent to an CROSS JOIN. Using an explicit CROSS JOIN is more intuitive and recommended, as it can easily be changed to a LEFT JOIN, RIGHT JOIN, etc. Using CROSS JOIN is also ANSI-compliant.
They are functionally equivalent. The second one is 'newer'.