db2 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 '

In the basic estimation process of all SQL statements, the calculation process of JOIN statements is the most complex, and JOIN statements are the focus of performance optimization. This article focuses on the calculation methods and inputs used by the DB2 optimizer for base estimation. Introduction The optimizer is the heart and soul of

The following articles mainly describe the result set estimation of JOIN statements in the DB2 optimizer. In actual operations, when the DB2 optimizer generates an execution plan for SQL statements, in actual operation, the result set generated by each step is estimated in size, which is the basis estimation of the optimizer. In the basic estimation process of al