There are 2 steps to solve this one. Solution Share Step 1 ANSWER : The time complexity of the merge sort algorithm is mainly determined by the number of recursive cal...View the full answer Step 2 Unlock Answer UnlockPrevious question Ne...
When an SQL statement is delivered, the QO compares the costs of redistribution and broadcast, and then generates an execution plan based on the algorithm. Optimization suggestion: If the table that you want to query is small and the instance contains a small number of shards, such as 5 ...
SELECT*FROMref_tableWHEREkey_column=exprORkey_columnISNULL; 7 index_merge:此类型表示使用了索引合并优化,表示一个查询里面用到了多个索引 8 unique_subquery:该类型和eq_ref类似,但是使用了IN查询,且子查询是主键或者唯一索引。例如: 代码语言:javascript 复制 valueIN(SELECTprimary_keyFROMsingle_tableWHEREsome...
为了更好的理解EXPLAIN,rows参数也是一个很好的参考,以下来自官网对rows的解释: Therowscolumn indicates the number of rows MySQL believes it must examine to execute the query. ForInnoDBtables, this number is an estimate, and may not always be exact. 这个字段表示MySQL认为执行查询必须检查的行数。 对...
We read every piece of feedback, and take your input very seriously. Include my email address so I can be contacted Cancel Submit feedback Saved searches Use saved searches to filter your results more quickly Cancel Create saved search Sign in Sign up Reseting focus {...
the library cache based upon a hashed representation of that query. When looking for a statement in the library cache, we first apply a hashing algorithm to the statement and then we look for this hash value in the library cache. This access path will be used until the query is reparsed...
(Storage Rows Scanned: 10000). Also, the data had to be sorted (viaSort Method: quicksort) on value (viaSort Key: value). You can improve this execution by modifying the above created index into a range index, so that you can avoid the sorting operation, and reduce the number of ...
In this case the leaves of the tree are implemented using a full table scans of the PRODUCTS and the SALES tables. The rows produced by these table scans will be consumed by the join operator. Here the join operator is a hash-join (other alternatives include nested-loop or sort-merge ...
DFEApply – Executes the function specified by functor in the arguments section, on the value stored in the specified variable DFEAlgoWriteProperty – Explain operator for the property-writing portion of mutate algorithm invocations. DFEBFSAlgo – Explain operator for invocations of the Breadth First...
However, if the data to be copied is too big, this can cost a lot, which MariaDB tries to avoid. Internal temporary tables are used in the following cases: For views that aggregate data, or are defined with the TEMPTABLE algorithm For UNION operations If both the ORDER BY and GROUP BY...