(1)sort 算子,会显示排序信息 Sort Method代表排序的方法,包括quicksort(快排)和disksort(外排)。快排即内存够用时,所有的排序操作均在内存中完成,外排说明当前可用内存不足,需要下盘。 (2)hashjoin算子 Buckets:代表hash表中实际使用的桶的个数 Batches:代表hashjoin中实际分块的数量。如果Batches=1,则说明所有...
<derivedN>:ID值n的行的派生表结果,派生表可能是从FROM子句中的一个子查询生成的(The row refers to the derived table result for the row with an id value of N. A derived table may result, for example, from a subquery in the FROM clause.)。 <subqueryN>:ID值n的行的物化子查询结果。 4....
先初步了解下Quicksort排序的概念(From Wikipedia). Quicksort is a divide and conquer algorithm. Quicksort first divides a large array into two smaller sub-arrays: the low elements and the high elements. Quicksort can then recursively sort the sub-arrays. The steps are: 1. Pick an element, c...
Filtered measures - filtered measures are visual level calculations with a specific filter applied (for example, Total Sales for France) and are used on some of the visuals created by the insights feature Categorical columns on X-axis unless it defines a sort by column that's scalar. If using...
Take an old electric toothbrush apart and it's easy to see how it works. I had one that didn't work anymore, so I had a quick look inside before taking it to the recycling center. Here's what I found:The first thing you notice is the removable brush. This is the bit that does ...
[CHOOSE] is an indication of the optimizer_goal for the query. This DOES NOT necessarily indicate that plan has actually used this goal. The only way to confirm this is to check the cost= part of the explain plan as well. For example the following query indicates that the CBO has been...
For example, headsets typically don't have screens and user interfaces that make it easy to select what computer or other device you want them to connect to, so you're often confronted by blinking lights and/or sounds to make it through the pairing process, with each device having its own...
Free Essay: Units help you better understand a problem because it gives you a basic understanding of what you're trying to solve. You can't just say "put two...
> > -- An example > > DROP TABLE IF EXISTS test; > > CREATE TABLE test (id1 int2, id2 int4, id3 int8, value varchar(32)); > > INSERT INTO test (SELECT i%11, i%103, i%1009, 'hello' FROM > > generate_series(1,1000000) s(i)); create statistics test_s1 on id1, ...
This causes an upward force on the magnet (white arrow) that slows it down like an invisible parachute.Here's an example. Suppose you drop a coin-shaped magnet down the inside of a plastic pipe. It might take a half second to get to the bottom. Now repeat the same experiment with a...