customNum=100 orderNum=200 rm tmp rm custom.sql for i in `seq $customNum`; do uuid=$(uuidgen) echo $uuid >> tmp done ## custom.sql文件为向t_custom表插入数据的sql awk -v LINE_NUM=$customNum 'BEGIN{ srand(); for(i=1;i<=LINE_NUM;i++) { a[i]=int(rand()*10000%100); ...
(1)order by clauses (2)group by (3)sort merge join –-这三个会产生排序运算 2.filter --过滤,如not in、min函数等容易产生 Has a number of different meanings, used to indicate partition elimination, may also indicate an actual filter step where one row source is filtering, another, functio...
2,执行计划有时预测数据量,不是真实运行,可能不准确 group by的MR hive语句最好写子查询嵌套,这样分阶段的导入数据,可以逐步减少数据量。但可能会浪费时间。所以需要设计好。groupby本身也是一种数据筛选,可以大量减少数据,尤其用于去重等方面,功效显著。但group by产生MR有时不可控,不知道在哪个阶段更好。尤其,map...
This number may be less than the number of columns present in the GROUP BY clause of the SQL statement if predicates eliminated the need to compare some columns. This argument can be associated with a GRPBY operator or with a TEMP operator when it is part of a query with multiple ...
Mysql SQL执行顺序与EXPLAIN FROM—>ON—>JOIN—>WHERE—>GROUP BY—>SUM(聚合函数)—>HAVING—>SELECT—>DISTINCT—>UNION—>ORDER BY—>LIMIT EXPLAIN 关键字分析 执行EXPLAIN SELECT * FROM device 加*号重点关注 代码语言:txt 复制 [\*]select\_type...
In this case the Optimizer assumes a uniform distribution and calculates the cardinality for the query by dividing the total number of rows in the table by the number of distinct values in the column used in the where clause predicate. Figure 9 shows a query running against the employees ...
order by clauses group by sort merge join Note that if the row source is already appropriately sorted then no sorting is required. This is now indicated in 7.3: SORT GROUP BY NOSORT INDEX FULL SCAN ... In this case the group by operation simply groups the rows it does not do the ...
T.SalesTerritoryGroup IN ('North America', 'Pacific') 14 AND Gender = 'F' 15 GROUP BY G.StateProvinceName, T.SalesTerritoryGroup 16 ORDER BY AVG(YearlyIncome) DESC</sql>17<dsql_operationstotal_cost="0.926237696"total_number_operations="9">18<dsql_operationoperation_type="RND_ID">19<...
explain select id, sum(moneys) from sales2 group by id order by null \G 1. 2. 你可以通过比较发现第一条语句会比第二句在Extra:里面多了Using filesort.而恰恰filesort是最耗时的。 优化ORDER BY语句 在某些情况中,MySQL可以使用一个索引来满足ORDER BY子句,而不需要额外的排序。WHERE 条件和 ORDER ...
Interpretable Prediction of Goals in Soccer Extending the Tsetlin Machine with Integer-Weighted Clauses for Increased Interpretability In Pursuit of Interpretable, Fair and Accurate Machine Learning for Criminal Recidivism Prediction From Shapley Values to Generalized Additive Models and back Developing A Visu...