所以Hash索引可以一次定位,其效率很高,而Btree索引需要经过多次的磁盘IO。 因为Hash索引比较的是经过Hash计算的值,所以在= in <=>(安全等于的时候)塔的效率是非常,但我们开发一般会选择Btree,Hash会存在如下一些缺点。 (1)Hash索引仅仅能满足"=","IN"和"<=>"查询,不能使用范围查询。 由于Hash 索引比较的是进...
* Explain a property, such as sort keys or targets, that takes the form of * a list of unlabeled items. "data" is a list of C strings. */voidExplainPropertyList(const char *qlabel, List *data, ExplainState *es){ ListCell *lc; bool first = true; switch (es->format) { case E...
This join type is similar to unique_subquery. It replaces IN subqueries, but it works for nonunique indexes in subqueries of the following form: index_subquery和unique_subquery很像,区别是它在子查询里使用的是非唯一索引。 valueIN(SELECTkey_columnFROMsingle_tableWHEREsome_expr) range Only rows tha...
"The maximum number of items to display in the carousel","possibleValues":null,"control":"INPUT","__typename":"PropDefinition"}],"__typename":"ComponentProperties"},"components":[{"id":"custom.widget.HeroBanner","form":{"fields":[{"id":"widgetChooser","validation":null,"n...
pattern– (Required) The pattern, which takes the form of a subject-predicate-object, and optionally -graph tuple that underlies the join. Ifdistinctis specified for the pattern, the join only extracts distinct solutions from projection variables specified by theprojectionVarsargument, rather than al...
In MySQL 8.0.17 and later, this can also indicate that a WHERE condition of the form NOT IN (subquery) or NOT EXISTS (subquery) has been transformed internally into an antijoin. This removes the subquery and brings its tables into the plan for the topmost query, providing improved cost pl...
1. Obsolete form of explanation. 2. Misspelling of explanation. explanationism 1. (philosophy) A philosophical system where beliefs are justified by their usefulness in explaining. explanans 1. A collection of propositions that, taken together, explain another proposition (the explanandum). 2. Ex...
A note on field/data access in objects: In order to access data in a object, some form of 'extractor' must be used. In the examples used in this tutorial aReflectionExtractoris used. The reflection extractor takes a method name, and applies it to a object to return a value. ...
ng-form and ng-submit in a ng-repeat I have been trying to get a nested form to validate properly and then call a function on my controller when the submit button is clicked. I have tried remove all buttons except the submit button and i......
There is no known process to get neutronium except in supernovae, so we have to assume the genie will simply start with a house-sized amount of neutronium, and added mass. This would quickly form a VERY SMALL black hole. Adding mass from here would put the material in the BH's ...