What is a SQL JOIN, and what are the different types?
What is SQL JOIN? SQL JOIN is a method to retrieve data from two or more database tables. What are the different SQL JOINs ? There are a total of five JOINs. They are : 1. JOIN or INNER JOIN 2. OUTER JOIN 2.1 LEFT OUTER JOIN or LEFT JOIN 2.2 RIGHT OUTER JOIN or RIGHT JOIN 2.3 FULL OUTER JOIN or FULL JOIN 3. NATURAL JOIN 4.
SQL JOIN: what is the difference between WHERE clause and ON …
The SQL INNER JOIN allows us to filter the Cartesian Product of joining two tables based on a condition that is specified via the ON clause. SQL INNER JOIN - ON "always true" condition If you provide an "always true" condition, the INNER JOIN will not filter the joined records, and the result set will contain the Cartesian Product of the two ...
SQL join syntax, when do you use "AS"? - Stack Overflow
2012年2月21日 · select t.year from HOUSE AS h LEFT OUTER JOIN SUBJECT K ON H.Name = K.Name INNER JOIN TESTCASE AS T ON k.year IS NOT NULL Sorry for the confusing example but basically - why am I able to use LEFT OUTER JOIN SUBJECT K without the keyword AS whereas with an INNER JOIN, I need to use a keyword of AS for INNER JOIN TESTCASE AS T?
SQL JOIN where to place the WHERE condition? - Stack Overflow
1. For INNER JOIN any condition can be in a WHERE instead of an ON as long as there is no intervening OUTER JOIN. 2. When moving a LEFT JOIN condition from an ON to a WHERE the performance is irrelevant since (as you say) in general the result differs. 3. That difference does not in general "transform the OUTER JOIN into an INNER JOIN". –
SQL Server Left Join With 'Or' Operator - Stack Overflow
2013年11月1日 · Here is what I did in the end, which got the execution time down from 52 secs to 4 secs. SELECT * FROM ( SELECT tpl.*, a.MidParentAId as 'MidParentId', 1 as 'IsMidParentA' FROM TopLevelParent tpl INNER JOIN MidParentA a ON a.TopLevelParentId = tpl.TopLevelParentID UNION SELECT tpl.*, b.MidParentBId as 'MidParentId', 0 as 'IsMidParentA' FROM TopLevelParent tpl INNER JOIN MidParentB b ON b ...
sql - Using AND in an INNER JOIN - Stack Overflow
2017年8月31日 · SELECT * FROM Table A A1 INNER JOIN TABLE B B1 ON B1.ID = A1.ID AND A1.SomeColumn = 'TASK'; And is the same as this. SELECT * FROM Table A A1 INNER JOIN TABLE B B1 ON B1.ID = A1.ID WHERE A1.SomeCoumn = 'TASK'; Whenever you join to a constant it is pretty much the same as adding an additional criterion to the where clause.
sql - JOIN two SELECT statement results - Stack Overflow
Is it possible to join the results of 2 sql SELECT statements in one statement? I have a database of tasks where each record is a separate task, with deadlines (and a PALT, which is just an INT of days from start to deadline. Age is also an INT number of days.)
SQL - How to do an IF/ELSE in JOIN conditions - Stack Overflow
2014年10月28日 · SELECT o.id, s.id FROM orders o RIGHT JOIN subjects s ON s.name = 'Blah' AND s.group_id = (CASE WHEN o.service = 'Law Services' THEN 2 ELSE s.group_id END) Share Improve this answer
MySQL JOIN ON vs USING? - Stack Overflow
The USING clause works for Oracle, PostgreSQL, MySQL, and MariaDB. SQL Server doesn't support the USING clause, so you need to use the ON clause instead. The USING clause can be used with INNER, LEFT, RIGHT, and FULL JOIN statements. SQL JOIN ON clause with SELECT * Now, if we change the previous ON clause query to select all columns using ...
sql - Condition within JOIN or WHERE - Stack Overflow
In "SQL Performance Tuning" by Peter Gulutzan and Trudy Pelzer, they tested multiple brands of RDBMS and found no performance difference. I prefer to keep join conditions separate from query restriction conditions. If you're using OUTER JOIN sometimes it's necessary to put conditions in …