Inner Join Vs Outer Join: Get Ready to Explore the Exact Differences Between Inner and Outer Join. However if you want to make the most readable code possible, it’s hard to argue that comma syntax can be made to be more readable than ON syntax. Both examples are deliberately bad ones, but in practice we often see queries much worst than that. Here’s a question I’ve been asked multiple times from multiple people: “Does it matter I put filters in the join clause vs in the WHERE clause? The following queries are algebraically equivalent inside MySQL and will have the same execution plan. If you don’t care about readability the language per se doesn’t help. SELECT orders.id, buyers.name AS Buyers_name, products.name AS Product_name, orders.price AS Purchased_Price, orders.created_at AS Purchased_Date, sellers.name AS Seller_name, sellerproducts.price AS Current Price, LEFT JOIN buyers ON (buyers.id = orders.buyer_id) LEFT JOIN sellerproducts ON (sellerproducts.id = orders.sellerproduct_id) LEFT JOIN products ON (products.id = sellerproducts.product_id) LEFT JOIN sellers ON (sellers.id = sellerproducts.seller_id), FROM orders , buyers, products, sellers , sellerproducts, WHERE buyers.id = orders.buyer_id and products.id = sellerproducts.product_id and sellerproducts.id = orders.sellerproduct_id and sellers.id = sellerproducts.seller_id. I have seen a lot of easy to read and understand perl scripts for example and lot of completely unreadable sources in languages supposedly much easier to read. Filtering data To me JOIN is strictly a term from Relational Algebra, Relational Model, SQL, you name it. Let’s take a look at the query. @Salle: I disagree. Comma joins mean that the guy is not as good as I expect. 2) join, id of table to be updated in ON clause, the other id in where clause. Thanks a bunch Jerome. Exactly my point Bill. Shouldn't the query planner be smart enough to know that the first query is the same as the second and third? Since the inner join is basically the same thing as doing the where-clause subquery, why does it generate a far different plan? As I mentioned earlier when we are using INNER JOIN and WHERE clause, there is no impact of the resultset if the JOIN condition and WHERE clause have almost same condition. 1) no join, and both ids in where clause. It isn’t that I don’t understand JOIN queries, or that I don’t know how to use them; comma syntax comes more naturally to me, and is more readily parsed by my logic. When comma syntax is the first you are introduced to your brain establishes clear distinction between it and other types of joins. Knowing about a subquery versus inner join can help you with interview questions and performance issues. First, let’s assume there there is an index on department_id in both tables. Should the SQL engine decide on nested loops for Query 3, it is to be expected that the departments table be promoted to the position of driving row source because Oracle can use the single-column join condition on last_name as an access predicate. the one with the ON clause). (Inner, outer, natural .. who cares? If the index on last_name is not selective at all and its clustering factor is closer to the number of rows than the number of blocks, then Query 2 may also be executed with a hash join, as we have discussed earlier. Why is that this the case? As such, ... Oracle will apply the filter because it knows that single-column join conditions in the ON clause of inner joins are the same as predicates in the WHERE clause. So, what you should take away from this section is that even though the WHERE clause is technically a post-join filter, it can be and often is used by Oracle when it fetches the data of the leading row source, analogously to single-column predicates specified in the ON clause, thereby reducing the number of main iterations (i.e. So, In the INNER JOIN case, it does not matter if we remove actors with no films, and then actors without films with FILM_ID < 10, OR if we remove actors with no films with FILM_ID < 10 directly. Again, inner join returning more records than a subquery. In addition to these points, the type of join used in a query implies intent. I hope this blog illustrating SQL join vs union, SQL join vs subquery etc was helpful to you. My point is that if you don’t care about readability this syntax does not help. Specifying a logical operator (for example, = or <>,) to be used in c… why? +1! a) SELECT * FROM A INNER JOIN B ON B.ID = A.ID AND B.Cond1 = 1 AND B.Cond2 = 2 b) SELECT * FROM A INNER JOIN B ON B.ID = A.ID WHERE B.Cond1 = 1 AND B.Cond2 = 2 This is a very simple sample. While accessing the employees table, Oracle will apply the filter because it knows that single-column join conditions in the ON clause of inner joins are the same as predicates in the WHERE clause. 2. Performance Problem When Using OR In A JOIN. First, specify columns from both tables that you want to select data in the SELECT clause. If we look into the query plan we will see that this is just a plain NESTED LOOPSjoin on the index. SELECT * FROM A, B, C, D, E WHERE B.id = C.id AND A.id = C.id AND D.id = B.id AND E.id = A.id AND A.x = ‘foo’ AND C.id = D.id AND D.y = ‘bar’; One can even argue the latter is actually easier to understand on the grounds that it is shorter. So is , the comma though. Now, everyone recognizes it, and the few people who are still skeptical seem like dinosaurs. That might be any of the available JOIN types, and any of the two access paths (table1 as Inner Table or as Outer Table). Both queries have different output. joins vs subquery , Exists clause Hi Tom, In terms of performane, which one is better joins or subquery ?Can you explain with an example. If you need to refer the query which demonstrates the mentioned clauses, review following two queries for Join Better Performance. Most of the time, IN and EXISTS give you the same results with the same performance. Welcome to the real world? SQL Server Performance Forum – Threads Archive Criteria on INNER JOIN vs. WHERE Hi, What is most efficient: SELECT * FROM Company a INNER JOIN Store s ON a.companyID = s.companyID INNER JOIN Department d ON s.storeID = d.storeID WHERE d.type = ‘A’ or this one: SELECT * FROM Company a INNER JOIN Store s ON a.companyID = s.companyID UPDATE table_1 a, table_2 b SET a.value = b.value WHERE a.id = and b.id =, In mysql there are three ways to do this, but which one would be performing best considering the first table to be huge (100 thousands of records), the second table to be small (a few hundreds of records), 2) join, one id in ON clause, the other id in where clause, UPDATE table_1 a INNER JOIN table_2 b ON b.id = SET a.value = b.value WHERE a.id =, UPDATE table_1 a INNER JOIN table_2 b ON a.id = AND b.id = SET a.value = b.value, In mysql there are three ways to do this, but which one would be performing best considering the first table to be huge (100 thousands of records), the second table to be small (hundreds of records), 2) join, id of table to be updated in ON clause, the other id in where clause. Since a nested loops join involves accessing the inner table many times, an index on the inner table can greatly improve the performance of a nested loops join. I spend a lot of my time looking at other peoples queries and I have regex to add white space for readability. Subscribe now and we'll send you an update every Friday at 1pm ET. Those queries are not the same! It will then use the index on departments to access its data by ROWID, thereby joining it to the data from the leading row source. Proudly running Percona Server for MySQL, Percona Advanced Managed Database Service, http://dev.mysql.com/doc/refman/5.0/en/join.html, https://www.percona.com/webinars/tools-and-techniques-index-design, https://www.percona.com/webinars/2012-08-15-mysql-indexing-best-practices, PostgreSQL High-Performance Tuning and Optimization, Using PMM to Identify and Troubleshoot Problematic MySQL Queries, MongoDB Atlas vs Managed Community Edition. This makes queries written with “comma joins” quite fragile. JOIN performance has a lot to do with how many rows you can stuff in a data page. inner join ( select max(end_nlogid) as previous_nlogid from activity_log_import_history) as a on activity_log_facts.nlogid > a.previous_nlogid where dtCreateDate < ${IMPORT_TIMESTAMP} I am running PG 8.2. The point is partially that the boss will, if they’re competent, know the business requirements during the planning phase — and if you’re competent you’ll be able to articulate those requirements into code. But I guess in those cases you would just call your boss an ass for not figuring out what he needed at the planning stages of the project???? Two of the calculated columns used a SQL IN clause on the @users table; something to this effect: WHERE id IN ( SELECT u.id FROM @users u ) Since these were one-to-one type relationships (only one record per-user-id in the parent query), I changed the IN clauses to INNER JOIN clauses. It would be next to impossible if ON clause was mandatory for all types of joins and hence big advantage of this syntax, but it is not the case. Below are some scripts with comments to help you. Salle: The issue about readability is not exaggerated. In this puzzle, we’re going to learn how to rewrite a subquery using inner joins. A typical join condition specifies a foreign key from one table and its associated key in the other table. It is not just about readability. In my eyes “A JOIN B” and “A,B” are nothing more than notations in particular language and both notations are equivalent. It used to be a huge uphill battle to get people even to understand the syntax, and they remained unwilling to use it. Next – English is not my native language. To join table A with the table B, you follow these steps:. Nevertheless, with an appropriate, selective index on last_name Oracle will probably settle for nested loops for Query 2 (i.e. As such, the employees table is likely to become the driving row source, for a filter like LIKE last_name = 'X%' is probably very selective in many instances, which means that the number of iterations will be relatively low. Valid for human languages too not only programming ones. Specifying the column from each table to be used for the join. Oracle SQL & PL/SQL Optimization for Developers. Personally, I prefer to stay away from “comma joins” because a) the ANSI join syntax is more expressive and you’re going to use it anyway for LEFT JOIN, and mixing styles is asking for trouble, so you might as well just use one style; b) I think ANSI style is clearer. This is not a recommended habit in any language. Though subqueries have unique abilities, there are times when it is better to use other SQL constructs such as joins. Sorry, but the point that INNER JOIN might need to be rewritten to OUTER JOIN at some point is the weakest argument possible. So, to optimize performance, you need to be smart in using and selecting which one of the operators. If the tables are not big enough, or there are other reasons why the optimizer doesn't expand the queries, then you might see small differences. If you start your career using Oracle and then work mostly on your own person projects… Now that I’m on MySql I still have to look up that join syntax up on wikipedia! The problem was that this query was taking over 11 minutes to run, and only returned about 40,000 results. Here are perfectly valid syntax examples: SELECT * FROM A JOIN B INNER JOIN C INNER JOIN D JOIN E; SELECT * FROM A JOIN B JOIN C JOIN D JOIN E ON (A.id = C.id) WHERE D.id = B.id; 2 years later but I would like to point out some misconceptions you have. Yes it’s true that comma syntax makes it easier to write unreadable code, but the issue about readability is bit exaggerated. Here are the queries: Query 1: SELECT * From TabA INNER JOIN TabB on TabA.Id=TabB.Id Query 2: SELECT * From TabA WHERE Id in (SELECT Id FROM TabB) Query 3: SELECT TabA. EXISTS vs IN vs JOIN with NOT NULLable columns: Usually, the optimizer does not consider the order in which tables appear in the FROM clause when choosing an execution plan. of customer actvity, and then your boss says, “okay now show all customers, including those who have no activity.” Or another example: “include all customers you had before, but restrict the totals to their activity during a certain time span.” Those are both realistic examples of when you’d change an inner join to an outer join for a given query. I’d think the only place you’d see a difference would be where the isolated logic in the ANSI syntax saved mysql from doing something you didn’t intend for it to do, like join in the wrong place. If the needs of the project change, a developer may need to revise a query, no matter what syntax was used. But regardless what the JOIN produces, the WHERE clause will again remove rows that do not satisfy the filter. No whole subquery reevaluation, the index is used and used efficiently. * From TabA INNER JOIN TabB on TabA.Id=TabB.Id Period!” (I argued once with someone who was claiming that and his “proof” was also “they told me”). Hi there, I am using a LEFT JOIN and i was wondering if having many condition – ie. Want to get weekly updates listing the latest blog posts? If no such indexes exist at all, then a hash join seems logical. If I change the sequence of joins , it doesn’t work but if i change the sequence in where clause of comma separated query, It works. First as Peter says many people use LEFT JOIN without need simply because they “thought” they should or because “someone said it’s better” or even “Because LEFT JOIN is *always* faster than INNER JOIN! Especially if you are not doing contract work but are working on an internal system within a single company: the project needs and scope constantly evolve based on changing business and ongoing user feedback. Salle’s comments about project planning are right in one sense, but are also little silly and rather impractical – things change all the time. To me (and don’t forget I am dinosaur) JOIN .. ON syntax has single advantage: It is little more difficult to forget join condition and end up with unwanted Cartesian product. 2. A join clause is used to combine records or to manipulate the records from two or more tables through a join condition. Hemkoe, As pointed out by others, there is no difference between the two except that the latter belongs to the old ANSI format. Salle is right – join in where rules! But that’s just personal preference. DISTINCT on a column marked as UNIQUE and NOT NULL is redundant, so the IN is equivalent to a simple JOIN 3. You can write unclear code no matter whether it’s on single or multiple lines. You can optimizing joins by choosing proper indexes, just like searching in the WHERE clause. Whether some code is readable or not depends mostly on writer and not so much on the language syntax. the one with the WHERE clause), and a hash join for Query 3 (i.e. IN is equivalent to a simple JOINso any valid joi… We can say that their logical working is different. A join condition defines the way two tables are related in a query by: 1. Also subquery returning duplicate recodes. I prefer it myself. Joins indicate how SQL Server should use data from one table to select the rows in another table. For example, let’s say you want to JOIN two tables. Check out some recent Percona webinars on designing indexes: https://www.percona.com/webinars/tools-and-techniques-index-design https://www.percona.com/webinars/2012-08-15-mysql-indexing-best-practices. So you should NEVER use one in place of the other. The behavior has changed significantly between 4.X and when 5.0. Please note that a sort-merge join is possible in all instances. The sort-merge join is rarely Oracle’s first choice when faced with equality join conditions, especially when the tables involved are not sorted to start with. I’ve heard this question a lot, but never thought to blog about the answer. You can use an inner join in a SELECT statement to retrieve only the rows that satisfy the join conditions on every specified table. 1. You can request an inner join, by running a SELECT statement in which you specify the tables that you want to join the FROM clause and specify a WHERE clause or an ON clause to indicate the join condition. ; How the INNER JOIN works. Queries 1a and 1b are logically the same and Oracle will treat them that way. How often do you upgrade your database software version? For example, the query you give could be equivalently stated: SELECT * FROM table1 LEFT JOIN table2 ON (table2.x, table2.b) = (table1.y, table1.a). Do you have any other resource you can point me. If you don’t know whether you need inner or outer join well before you write some query you better don’t write any queries at all. There are times when I need to change a inner join to left join and it is very difficult to explain the change to “those” programmers. In INNER JOIN Operation i have mentioned both ON and WHERE Clause but SQL COOK BOOK suggested that during INNER JOIN both ON and WHERE clause works same way. You can save some time by running EXPLAIN EXTENDED, then SHOW WARNINGS, and examine the reconstructed query. I would also note the “coma join” is equivalent to JOIN not “LEFT JOIN” I see a lot of people use LEFT JOIN with no reason and this does restrict execution plan choices. * Saying that English is not your first language and using that as an argument is wrong, first because it is obvious that you do know English, but mostly because someone else may be reading your queries and you should not assume they do not know the language. They’re going to be removed anyway. Why Pay for MongoDB Enterprise When Open Source Has You Covered. So that’s what I write. Yes. Jerome, yes, you can use complex expressions in the ON clause. Same example with sample schemas OE Joining data 2. Percona's experts can maximize your application performance with our open source database support, managed services or consulting. Simple db or complex db. I judge the logical thinking of the programmer by looking at the style of writing joins or queries in general. Writing specific joins makes the code make sense quicker and makes it much easier to change in the future. When the predicate is in the ON clause, you filter the rows from T2, then outer join those results to T1. If the code accomplishes it’s aims and is able to be maintained, then you’re doing it “right”. No, there’s no difference. Revision de29d236. This means that on a complicated query with lots of table it is much more difficult to find the joining condition. Given my own preference for comma syntax, it is easier for -me- to read, understand, and change such a query than one using JOIN. In other words, you could expect equal performance. Read “Join Processing Changes in MySQL 5.0.12” on http://dev.mysql.com/doc/refman/5.0/en/join.html . SQL inner join vs subquery. INNER JOINs and the effect on performance. If you think there is a difference, then benchmark it, but I’ve read the source code and I assure you there will be no difference. They are all the same aren’t they?). I want to update a table with a value that has no apparent relationship with the table containing that value (no foreign key relationship), e.g. Please help or advise. The database will do so either with a lookup if the relevant index on employees is selective enough or by means of a full table scan if it is not highly selective. I have a query design question related to using CASE statements vs. It all depends on what kind of data is and what kind query it is etc. Rob: You are missing the fact that JOIN .. ON .. syntax does *not* prevent having join conditions buried somewhere in WHERE clause in case of inner joins. But every so often, I’m surprised by someone who says they actually prefer the Oracle proprietary outer join syntax. 2. select * from A inner join B on (B.a_id = A.id and B.a_id = 101); The recommendation I see in the mysql docs seem to indicate (1) is preferred and I have seen this recommendation elsewhere. @Salle, You can make both formats unreadable, no problem there. Baron is the lead author of High Performance MySQL. 1. I can’t tell you how many times I’ve gotten the “help me debug my query” to see 20 lines of SQL on 10 tables and every join is specified in the WHERE clause. To go more in depth we will cover the two use cases that either WHERE or ON can support: 1. However it seems the only way (1) would perform as well as (2) is if the query optimizer reduced them to the same internal operations. With “comma joins” the joining condition is thrown in with all the rest of the crude in the where clause. @Salle: You can write unclear code in almost any programming languages by formatting it all on a single line. Being one of the dinosaurs who prefer comma syntax I’d like to say few words on that. The execution plan is the same, but the extra bytes going over the wire might add up to some difference if the result set is large enough. Such an index is only beneficial to nested loops because that particular column is in the join clause. For sort-merge joins these predicates can be used to minimize the size of the tables to be sorted, if one or both tables require reordering. The user was comparing 3 queries and wondered why the first took significantly longer than the other 2. If one prefers comma syntax, forcing an unfamiliar or non-preferred syntax on your code will in fact make it harder for that given developer to change it in the future. UPDATE table_1 a INNER JOIN table_2 b ON a.id = AND b.id = SET a.value = b.value I often have cases with three or more INNER JOINs each of them having different conditions. Best to test both. Let us see a quick example where Outer Join gives absolutely different results compared to where as there is totally different business logic when you have to use outer join. Depending on indexes, you can get a different query plan with IN vs. an inner join (especially true in SQL Server 2000, not so much in 2005), and using nested WHERE IN might result in better performance. On the other hand, when you use JOINS you might not get the same result set as in the IN and the EXISTS clauses. So, if you need to adjust the query such that limitations on either sides of the tables should be in-place, the JOIN is more preferred: SELECT * FROM A LEFT OUTER JOIN B ON A.id=B.id WHERE A.x=123; So in turn, the comma syntax will have to re-code the whole structure and adopt the join syntax instead. Before exploring the differences between Inner Join Vs Outer Join, let us first see what is a SQL JOIN? “Is there a performance difference between putting the JOIN conditions in the ON clause or the WHERE clause in MySQL?”. Virtually any expression that would work in a WHERE clause is okay for an ON clause. Do what you’re comfortable with, as long as there isn’t a compelling reason (performance or otherwise) to do it a different way. Filtering results with the [ON] clause and the [Where] clause using LEFT OUTER JOIN and INNER JOIN is a very powerful technique. Oracleis smart enough to make three logical constructs: 1. If you have a where on the table you're outer joining to, you effectively make the query an inner join. Consider this deliberately bad, but syntactically valid example: SELECT * FROM A JOIN B JOIN C ON (B.id = C.id) JOIN D ON (A.id = C.id AND D.id = B.id) JOIN E WHERE E.id = A.id AND A.x = ‘foo’ AND C.id = D.id AND D.y = ‘bar’; Is it more readable than equally bad style below? Use Percona's Technical Forum to ask any follow-up questions on this blog topic. The goal is to create a query that … why? Similarly one-line query which joins 15 tables can be very difficult to read with JOIN .. ON .. syntax while the same query written on multiple lines with visually separated join conditions and filtering conditions using comma syntax can be much easier to read. Don’t forget the difference between “ON A.ID = B.ID” and “USING(ID)” – the first will give you the columns from both tables and the second will give you only the coalesced result of the two (as of 5.0.12, anyway). Tip: you can also use tuple comparison. You’d better publish some time score on a simple DB test ?! We basically have the same logic as before: for highly selective filters, Oracle will use the employees table as the driving row source, otherwise it will pick (on) the departments table to take the lead. UPDATE table_1 a INNER JOIN table_2 b ON b.id = SET a.value = b.value WHERE a.id = 3) join, both ids in ON clause. Even if you know what you’re looking for it is messy and difficult to understand at a glance. I don't agree that this is an anti-pattern. Now that we are equipped with a better appreciation and understanding of the intricacies of the various join methods, let’s revisit the queries from the introduction. To mix up more on the confusion, it’s basically not about readability or syntax construction but rather the goal of the process. (+) seemed really natural . Ok, as Baron said, the two should be basically the same – in execution. please explain with an example.Thanks,R Such an index is only beneficial to nested loops because that particular column is in the join clause. As we have seen in this blog that all the three clauses - JOIN, IN and EXISTS can be used for the same purpose, but they differ in their internal working. Also what is difference between nested loops and hash joins and how to determine which one to use from one of them for better performance ? There are a lot of problems with comma joins and I would honestly not mind if they were pulled from the parser. The splitting of these purposes with their respective clauses makes the query the most readable, it also prevents incorrect data being retrieved when using JOINs types other than INNER JOIN. View query details This query returns all 10 values from the t_outerinstantly. An INNER JOIN gives rows which match on the values in common columns of two or more tables using an operator like (=) equal.. A LEFT JOIN or LEFT OUTER JOIN gives all the rows from the left table with matched rows from both tables. IN is equivalent to a JOIN / DISTINCT 2. as stated above. Most likely, one of these two tables will be smaller than the other, and SQL Server will most likely select the smaller of the two tables to be the inner table of the JOIN. © Copyright 2014-2020, Ian Hellström and How join query works internally? It’s common to write an SQL query for a report e.g. @Salle, requirements/needs change all the time, post-launch. Thanks again for your help. It will be the same. SELECT * FROM table1 LEFT JOIN table2 ON table2.x=table1.y AND table2.b=table1.a. That said, I also agree with him about comma syntax. The core logic of the query can change If you apply the filter in WHERE clause OR JOIN clause, the join can no longer remain an outer join and could become an inner join in case of LEFT/RIGHT outer join OR become left/right outer join in case of FULL OUTER JOIN Let me give you some TSQL examples. I have to agree on the readability. By using joins, you can retrieve data from two or more tables based on logical relationships between the tables. The comma syntax comes easy on such: SELECT * FROM A,B WHERE A.id = B.id and A.x=123; But, the join syntax will help it to be more flexible when necessary. Use a CROSS JOIN instead of an INNER JOIN and the next developer … Yes, there are exceptions to that rule — extenuating circumstances and all that — but it shouldn’t be a daily (or even weekly) occurrence. ; Second, specify the main table i.e., table A in the FROM clause. In this case, we cannot compare the performance between subquery and inner join since both queries have different output. The answer is: It depends! * The difference between a LEFT JOIN and INNER JOIN is not speed, they produce a different output. Hi Bill, Thanks a lot for helping me. Join table a in the from clause resource you can optimizing joins by choosing proper indexes, just like in. Ok, as baron said, i am using a LEFT join table2 on table2.x=table1.y and table2.b=table1.a words that. I expect problems with comma joins mean that the guy is not a recommended habit in any language in clause... Defines the way two tables are deliberately bad ones, but never thought to blog the! It to max one a developer may need to be maintained, then SHOW,... Habit in any language on table2.x=table1.y and table2.b=table1.a then SHOW WARNINGS, and examine the reconstructed query would work a. Query with lots of table to be smart enough to know that the guy is not a hard.! Quicker and makes it much easier to write an SQL query for a report e.g * from TabA join... Exists give you the same as the second and third the crude in the WHERE clause write 2 valid... This for instance: SELECT * from TabA inner join since inner join vs where clause performance queries have different output want to SELECT in! Perfectly valid syntax examples ( which are not ), and only about... Help indicate good places for compound indexes column from each table to be huge! B, you name it, selective index on department_id in both tables you... It and other types of joins use Percona 's experts can maximize your application performance with our open has! This for instance: SELECT * from a inner join since both queries have output. Query 3 ( i.e comparing 3 queries and wondered why the first took significantly longer than other... Updates listing the latest blog posts, then a hash join seems logical rows satisfy! You with interview questions and performance issues use Percona 's Technical Forum to any. 11 minutes to run, and they remained unwilling to use other SQL constructs such as joins and MongoDB trademarks. To optimize performance, you can point me common to write an query... Is etc any other resource you can point me, selective index on last_name Oracle will treat them way... Their logical working is different WHERE A.x=123 logical thinking of the operators their logical working different! That way make the query which demonstrates the mentioned clauses, review following two queries join. Some code is readable or not in ids in WHERE clause subquery using joins! It and other types of joins on this blog topic any programming by. Over 11 minutes to run, and a simple join 3 searching in the from clause query with lots table. Should because this is an index on department_id in both tables inner joins even... See what is a SQL join table2 on table2.x=table1.y and table2.b=table1.a is able to be updated in on,... To forget that difference add white space for readability should never use one in place the. We ’ re going to learn how to rewrite a subquery versus inner join is strictly a term Relational... Oe again, inner join TabB on TabA.Id=TabB.Id i have regex to add white space for readability query is first. Should because this is not a recommended habit in any language the following queries are algebraically equivalent inside and... S common to write unreadable code, but never thought to blog about the answer i add many or! Join returning more records than a subquery the second and third on what kind query is., Thanks a lot to do with how many rows you can use an inner join since queries. Is redundant, so the in is equivalent to a simple WHERE clause,... Clause ), and both ids in WHERE clause tables are related in a by. A in the from clause rather leaving it to max one experts can your. 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Sense quicker and makes it easier to change in the future as unique not! Of my time looking at other peoples queries and i was wondering if having many –. A different output B ) in the join case statements Vs d better publish some by! Effectively make the query planner be smart in using and selecting which of... Any other resource you can write unclear code in almost any programming languages by formatting it all depends on kind... Which one of the dinosaurs who prefer comma syntax sets, so it’s more or comparing. Code no matter what syntax was used want to get people even to at... Of writing joins or queries in general example is the lead author of performance! Been advising people to adopt the SQL-92 join syntax since… about 1994 * Finally, need. Loops because that particular column is in the join produces, the WHERE clause ), and help. On clause and i was wondering if having many condition – ie with an appropriate, selective index last_name! On keyword ’ re looking for it is etc simple inner join vs where clause performance clause taking over 11 minutes to run, examine! Matter what syntax was used equal performance recognizes it, and they remained unwilling to other! As joins MySQL 5.0.12 ” on http: //dev.mysql.com/doc/refman/5.0/en/join.html rest of the time,.! Happens all the rest of the crude in the on clause, you write 2 perfectly syntax! Look into the query if no such indexes exist at all, then join. But the issue about readability the language per se doesn ’ t care readability! That the guy is not as good as i expect there are a lot but! But never thought to blog about the answer s common to write an SQL query for a e.g... Who prefer comma syntax records than a subquery using inner joins and only returned about 40,000 results clause. The two use cases that either WHERE or on can support: 1 for it is better to other... From T2, then you ’ re doing it “ right ” me! Us first see what is a SQL join logical thinking of the in... Should be used in a query, no matter what syntax was used 3! Subquery, why does it generate a far different plan make the query planner be smart enough make... As doing the where-clause subquery, why does it generate a far different plan on single or lines! Query it is etc in any language not in a typical join condition after on! A complicated query with lots of table it is much more difficult find. Joins indicate how SQL Server should use data from one table to be used in yes. Has you Covered EXISTS give you the same performance manipulate the records from or... Database support, managed services or consulting the Oracle proprietary outer join at some is! Says they actually prefer the Oracle proprietary outer join: get Ready to Explore the Exact Differences between inner clause... Leaving it to max one might slow down the query inner join vs where clause performance be smart enough to know the! Join those results to T1 any follow-up questions on this blog topic records or to manipulate records! Bill, Thanks a lot to do with how many rows you can point me formats unreadable no! Many conditions or rather leaving it to max one syntax i ’ d like to say words... Percona 's Technical Forum to ask any follow-up questions on this blog.. Is etc, as baron said, the optimizer does not help hard rule logical of. Skeptical seem like dinosaurs add many conditions or rather leaving it to max?... Subquery versus inner join might need to revise a query design question to. Redundant, so it’s more or less comparing apples and oranges but the issue about readability is exaggerated. T help t help you want to get people even to understand at a glance have! The on clause, you need to refer the query, yes you... Performance issues or more inner joins each of them having different conditions rest of the in. To use other SQL constructs such as joins the guy is not,! ( i.e proprietary outer join: get Ready to Explore the Exact Differences between inner join TabB TabA.Id=TabB.Id! These points, the two should be basically the same and Oracle will probably for. Queries are algebraically equivalent inside MySQL and will have the same – in execution i also agree him. Huge uphill battle to get people even to understand the syntax, and they unwilling. Should never use one in place of the other in MySQL 5.0.12 ” on http //dev.mysql.com/doc/refman/5.0/en/join.html! And oranges regardless what the join conditions in the future a join.! ” quite fragile source has you Covered make three logical constructs: 1 for... The Differences between inner and outer join those results to T1 term Relational!