92_MySQL_执行计划_ref_or_null是小白必学技术MySQL,MySQL8全套教程,使用JDBC操作MySQL,熟练使用MySQL,Navicat,JDBC。的第92集视频,该合集共计103集,视频收藏或关注UP主,及时了解更多相关视频内容。
select * from demo_table where key1 = 'abc' OR key1 is NULL; 当使用二级索引而不是全表扫描的方式执行该查询时,对应的扫描区间就是[NULL,NULL]和[‘abc’,‘abc’],此时这种类型的查询所使用的访问方法就称为ref_or_null。 4、range 有时候,我们的查询方法很复杂,比如下面这个sql select * from de...
type显示的是访问类型,是较为重要的一个指标,结果值从好到坏依次是: system> const > eq_ref > ref > fulltext > ref_or_null > index_merge > unique_subquery > index_subquery > range > index >ALL 一般来说,得保证查询至少达到range级别,最好能达到ref。 possible_keys 指出MySQL能使用哪个索引在该...
type显示的是访问类型,是较为重要的一个指标,结果值从好到坏依次是: system > const > eq_ref > ref > fulltext > ref_or_null > index_merge > unique_subquery > index_subquery > range > index > ALL ,一般来说,得保证查询至少达到range级别,最好能达到ref。
ISERR() : 如果参数的结果是(#VALUE!, #REF!, #DIV/0!, #NUM!, #NAME?, or #NULL! ), 则结果是TRUE, 否则结果是FALSE ISERROR() : 如果参数的结果是(#N/A, #VALUE!, #REF!, #DIV/0!, #NUM!,#NAME?, or #NULL! ), 则结果是TRUE, 否则结果是FALSE 所以“ISERR”和“ISERROR”的区别就...
, #REF!, #DIV/0!, #NUM!, #NAME?, or #NULL! ), 则结果是TRUE, 否则结果是FALSE 所以“ISERR”和“ISERROR”的区别就是:“ ISERROR”比“ISERR”函数多判断一个"#N/A"值 (也就是说: = ISERR(NA()) 的结果是FALSE; 而 = ISERROR(NA())的结果是TRUE. 而ISNA就只能判断参数是不是#N/A.下...
5 or assembly null of centrifugal compressor for 8kW refigerating plant and the said(57) [summary] condenser, evaporator, 8kW refrigeration unit and with a assembly of a two-stage centrifugal compressor with electric motor with a cooler. While being connected to the outlet of the assembly of ...
The demand for projects to cut health costs or increase health quality exceeds any healthcare CIO's capacity to deliver, making effective prioritization essential. Healthcare payer and provider CIOs can use Gartner's best practices to scrutinize, select
log('CHART REF', chartRef.current) return ( <Bar ref={chartRef} type="bar" height={chartHeight} data={data} options={options} /> ) } The issue is that chartRef.current is either null or undefined, and one way to have a value for it is to resize the window. 👍 3 ...
I load a model into a tensorflow.js to classify images,but it returns:"Unable to get property 'length' of undefined or null reference", message: "Unable to get property 'length' of undefined or null reference", number: -2146823281, stack: "TypeError: Unable to get property '...