sql - What is SELF JOIN and when would you use it? - Stack Overflow
Jun 13, 2024 · You use a self join when a table references data in itself. E.g., an Employee table may have a SupervisorID column that points to the employee that is the boss of the current employee. To query the data and get information for both …
sql - Explanation of self-joins - Stack Overflow
Jun 15, 2024 · Here is the exaplanation of self join in layman terms. Self join is not a different type of join. If you have understood other types of joins (Inner, Outer, and Cross Joins), then self join should be straight forward. In INNER, OUTER and CROSS JOINS, you join 2 or more different tables. However, in self join you join the same table with itslef.
sql - Purpose of Self-Joins - Stack Overflow
Apr 20, 2017 · I found self joins most useful in situations like this: Get all employees that work for the same manager as Sam. (This does not have to be hierarchical, this can also be: Get all employees that work at the same location as Sam) select e2.employeeID, e2.name from employee e1 join employee e2 on (e1.managerID = e2.managerID) where e1.name = 'Sam'
sql - When do we need self join exactly? - Stack Overflow
May 13, 2015 · Another place where self join really comes in handy is say when you want to join a record with a date column and check if subsequent rows have same value. EDIT - Answering the question in the comment. So, for example you have records like. ValueCol DateCol 25 '12/31/2014' 25 '1/1/2015' 30 '1/2/2015' Your self join will look like:
Comparing SQL Table to itself (Self-join) - Stack Overflow
Mar 2, 2015 · Do not JOIN on an inequality; it seems that the JOIN and WHERE conditions are inverted. SELECT t1.id FROM Test t1 INNER JOIN Test t2 ON ((t1.test1 = t2.test2) OR (t1.test2 = t2.test1)) WHERE t1.id <> t2.id Should work fine.
sql - Self-Join with Natural Join - Stack Overflow
May 25, 2018 · The difference between those two statements is that the second explicitly defines a self join on the table, where the first statement, the optimizer is trying to figure out what you really want. On my database, the first statement performs a cartesian merge join and is not optimized at all, and the second statement has a better explain plan ...
Self Join + Left Join in Sql Server - Stack Overflow
Jun 27, 2017 · Self Join + Left Join in Sql Server. Ask Question Asked 7 years, 7 months ago. Modified 7 years, 7 months ago.
sql - Optimize self join on millions of rows - Stack Overflow
Dec 30, 2012 · SQL self-join optimization. 0. Optimization of large SQL query with lots of joins. 1. Need suggestion on ...
sql - Self-join of a subquery - Stack Overflow
Apr 11, 2019 · SQL self join result of a select. 0. converting subquery to join in postgresql. 2. sql self join on ...
sql - Self join with inner and outer join query - Stack Overflow
Mar 7, 2013 · You have to move the date comparison to the join condition: select ta1.attribute '1st Name' , ta2.attribute 'last name' , ta3.attribute 'account#' from tblAccount ta1 inner join tblAccount ta2 on ta1.entity = ta2.entity and ta1.attributetype = 1 and ta2. attributetype = 2 and ta1.enddate > getdate() and ta2.enddate > getdate() left join tblAccount ta3 on ta1.entity = ta3.entity and ta3 ...