The join type.For descriptions of the different types, see EXPLAIN Join Types. --对表所使用的访问方式。 2.1.5 possible_keys Thepossible_keys column indicates which indexes MySQL can choose from use to findthe rows in this table. Note that this column is totally independent of theorder of th...
CHAPTER 4RELATIONALDATABASESSUGGESTED ANSWERS TO DISCUSSION QUESTIONS 4.1 Contrast the logical and the physical view of data and discuss why separate views are necessary indatabaseapplications. Describe which perspective is most useful for each of the following employees: a programmer‚ a ma...
Assumethat is defined as NOT NULL. In this case, MySQL scans t1 and looks up the rows in t2 usingthe values . If MySQL finds a matching row in t2, it knowsthat can never be NULL, and does not scan through the rest of the rows in t2 thathave the same id other words, for each ...
They test scenarios where the code interacts with external systems, databases, or complex dependencies. Mocking or stubbing test cases help isolate and test specific units of code independently by replacing external dependencies with controlled simulated objects.Performance...
The table towhich the row of output refers. --显示这一步所访问的数据库中的表的名称 2.1.4 type The join type.For descriptions of the different types, see EXPLAIN Join Types. --对表所使用的访问方式。 2.1.5 possible_keys Thepossible_keys column indicates which indexes MySQL can choose from...
The content of the derived table is rematerialized to bring it up to date each time a new row of t is processed by the top query. Scanned N databases (JSON property: message) This indicates how many directory scans the server performs when processing a query for INFORMATION_SCHEMA tables...
The concept of an index in MongoDB is the same as in relational databases. An index is generally a small structure—in comparison to the collection size—that provides a better way to access documents more quickly. Without an index, the only way that MongoDB has to retrieve the documents ...
The content of the derived table is rematerialized to bring it up to date each time a new row of t is processed by the top query. Scanned N databases (JSON property: message) This indicates how many directory scans the server performs when processing a query for INFORMATION_SCHEMA tables...
Database Examples, Schema & Types | What is a Database? from Chapter 11 / Lesson 12 724K What are databases? Learn about the different types of databases and what database management systems are. Also learn about database software a...
Database Examples, Schema & Types | What is a Database? from Chapter 11 / Lesson 12 724K What are databases? Learn about the different types of databases and what database management systems are. Also learn about database software and challenges. Related...