The outer join basically creates the same resulting set as the inner join, with the difference that at least one line is created in the resulting set for every selected line on the left-hand side, even if no line on the right-hand side fulfils the join_cond condition. The columns on ...
Append [All |Distinct]saveAppend used with Subquery Scan to implement UNION and UNION ALL queries. Can operate from disk based on virtue of "save". Miscellaneous/Other: HashhashUsed for inner joins and left and right outer joins (provides input to a hash join). The Hash operator creates th...
It is true (of course) that the WHERE clause sorts out the LEFT OUTER JOIN (thanks). The only niggle is I remember moving the a.batch = 105 from a WHERE to the JOIN for what was a valid reason at the time but cannot remember the details now. Perhaps I should leave both in???
* Create a new ExplainState struct initialized with default options. */ExplainState *NewExplainState(void){ ExplainState *es = (ExplainState *) palloc0(sizeof(ExplainState)); /* Set default options (most fields can be left as zeroes). */ es->costs = true; /* Prepare output buffer. ...
You can also useEXPLAIN to check whether the optimizer joins the tables in an optimal order. Togive a hint to the optimizer to use a join order corresponding to the order inwhich the tables are named in a SELECT statement, begin the statement with SELECTSTRAIGHT_JOIN rather than just ...
Data in other to-be-joined tables is read by row, hash calculated, and matched with data in the hash table. Matched data is returned. The following table describes the categories of hash joins. Category Description Hash Left Join When multiple tables are joined, all rows in the left table...
00 | root | | CARTESIAN left outer join | | ├─TableReader_16(Build) | 10000.00 | root | | data:TableFullScan_15 | | │└─TableFullScan_15 | 10000.00 | cop[tikv] | table:t1 | keep order:false, stats:pseudo | | └─Limit_17(Probe) | 10000.00 | root | | offset:0, ...
Enables recursive property paths such as+or*. Neptune implements a fixed-point iteration approach based on a template specified by theiterationTemplateargument. Known left-side or right-side variables are bound in the template for every fixed-point iteration, until no more new solutions can be fou...
above. As an analogy to the coding world, you can look at the concept of an inner join as very similar to a nested loop. MySQL chooses the table it thinks will be best to start the journey with (the outer "loop") and then touches the next table using the values from the outer "...
Here is an example of the type of query that can be optimized this way: SELECT * FROM t1 LEFT JOIN t2 ON t1.id=t2.id WHERE t2.id IS NULL; Assume that t2.id is defined as NOT NULL. In this case, MySQL scans t1 and looks up the rows in t2 using the values of t1.id. ...