postgresql outer join

1, left outside the connection to leave outer join, or leaving Jion,outer can be omitted to write, the bottom of the right connection and full connection is the same:The left outer join means that the data in the table on the left side of the right

1. Left OUTER JOIN: External Association SELECT E.last_name, e.department_id, D.department_name From Employees E Left OUTER JOIN Departments D On (e.department_id = d.department_id); Equivalent to SELECT E.last_name, e.department_id, D.department_name From Employees e, departments D WHERE e.department_id=d.department_

Recent BA user feedback has two seemingly very similar statements return the number of results is not the same, more strange, doubt is not hive bug Query 1 Returns the number of results 6071 Select COUNT (Distinct reviewid) as dis_reviewcnt from (select A.reviewid from bi.dpods_dp_reviewreport a left outer join Bi.dpods_dp_reviewlog B on a.reviewid=b.reviewid and b.hp_statdate= ' 2013-07-24 '

Oracle and postgresql join methodFirst, we will introduce several oracle multi-Table Connection Methods:Nested loop: nested loop, which is actually a dual FOR LOOP1. The driver table (External table) and search table (internal table) are divided here)2. To search for a table with an index, you can use an index to find and match the table, improving the efficiency,3. Use a small table as the driving table4.

User_info to correlate information from other social tables, but other social forms may not have this user Select U.*, Coalesce (U.slogan, Tw.description, I.bio, g.bio,tu.description) as bio from User_info u Left OUTER join Twitter_user tw on u.user_name = Tw.screen_name left OUTER join Instagram_user i on u.user _nam

As long as one of the tables has a match, the full JOIN keyword returns rows. Full JOIN keyword syntaxSELECT column_name (s)From table_name1Full JOIN table_name2On Table_name1.column_name=table_name2.column_nameNote: In some database tutorials, the full join is called the full OUT