EXPLAIN Join Types# Explain返回值中的type字段的含义,它揭示了表是如何被连接的(在MySQL中即使是单表查询也被抽象成关联查询)。 下面是该字段可能的值,从情况好到坏排序: system# 官方的说法是在表只有一行时它会被看作“系统表”,这时查询就是system类型,不过我构建了一行的表,也查询了MySQL中的只有一行的系...
Answer to: Explain the basic concepts of an accounting information system. By signing up, you'll get thousands of step-by-step solutions to your...
Journal of the Association for Information SystemsLowry, P. B., Gaskin, J. E., and Moody, G. D. 2015. "Proposing the Multimotive Information Systems Continuance Model (MISC) to Better Explain End-User System Evaluations and Continuance Intentions," Journal of the Association for Information ...
A four level pyramid model of different types of Information Systems based on the different levels of hierarchy in an organization. The first level represents transaction processing systems for workers. The second level represents management information systems for middle managers. The third level ...
Explain why cells in the intestinal lumen have microvilli. Describe the function of type I alveolar cells. List and describe the functions and processes that occur in the digestive system. Explain the functions associated with the low pH environment of the stomach. ...
MySQL explains how it would process the statement, including information about how tables are joined and in which order. For information about using EXPLAIN to obtain execution plan information, see Section 8.8.2, “EXPLAIN Output Format”. 当EXPLAIN与可解释语句一起使用时,MySQL将显示来自优化器的关...
1 system:该表只有一行(相当于系统表),system是const类型的特例 2 const:针对主键或唯一索引的等值查询扫描, 最多只返回一行数据. const 查询速度非常快, 因为它仅仅读取一次即可 3 eq_ref:当使用了索引的全部组成部分,并且索引是PRIMARY KEY或UNIQUE NOT NULL 才会使用该类型,性能仅次于system及const。
aSo a theory of service systems should explain what service systems are and aren’t, how they arise and evolve, the relation between internal and external service systems, and the role of people, technology, value propositions, and shared information in the system. 이렇게 서비스 체...
The EXPLAINstatement provides information about the execution plan for a SELECT statement. EXPLAIN returnsa row of information for each table used in the SELECT statement. It lists thetables in the output in the order that MySQL would read them while processingthe statement. MySQL resolves all joi...
One row is read from this tableforeach combination of rows from the previous tables.Other than the system and const types, this is the best possible join type. It is used when all parts of an index are used by thejoinand the index is a PRIMARY KEY or UNIQUE ...