文章目录 explain执行计划结果分析 0、id 1、select_type 2、table 3、partitions 4、type 5、possible_keys 6、key 7、key_len 8、ref 9、rows 10、filtered 11、Extra explain分析出的索引一定是最优的吗? explain执行计划结果分析 在MySQL中,我们可以通过explain命令查看sql... ...
文章目录 explain执行计划结果分析 0、id 1、select_type 2、table 3、partitions 4、type 5、possible_keys 6、key 7、key_len 8、ref 9、rows 10、filtered 11、Extra explain分析出的索引一定是最优的吗? explain执行计划结果分析 在MySQL中,我们可以通过explain命令查看sql...mysql...
Describe the use of keys in a database. Can you have more than one key? Explain.Question:Describe the use of keys in a database. Can you have more than one key? Explain.Keys in a databaseA key is an set of data base which is designed to recognize rows and...
Foreign Keys:A database table must have a primary key and may also have foreign keys. When a database is normalized the data will appear only once in one table and will not be duplicated in another table.Answer and Explanation: Become a member a...
EXPLAIN PLAN output shows how Oracle Database would run the SQL statement when the statement was explained. This plan can differ from the actual execution plan a SQL statement because of differences in the execution environment and explain plan environment. Note: To avoid possible SQL performance ...
FILTER_PREDS VARCHAR2INDEFAULT FUNCTIONDISPLAY_AWRRETURNSDBMS_XPLAN_TYPE_TABLE DISPLAY_AWR函数显示存储在AWR历史数据的执行计划。 提示:要正常调用DISPLAY_AWR 参数,必须对以下视图有权限:DBA_HIST_SQL_PLAN 和DBA_HIST_SQLTEXT 的SELECT。 参数名称 类型 输入/输出默认值?
The supplemental log data contains at least additionally the primary/unique key like on the picture. In the absence of primary/unique keys, every column of a modified row is written into the redo logs.That may impact the performance of the primary database.Another serious drawback of Logical ...
三、 DBMS_XPLAN包 除了结合explain plan命令外... explain;来获取执行计划,这种方法虽然也执行了sql语句,但是执行计划不一定是真实的。 引用一个经典的例子(不是我做的)来证明:autotrace on和explain plan的结果是使用index SQL优化 第二章 执行计划 calls)可以方便看到。 3 EXPLAIN PLAN 当某个性能SQL死掉,...
Explain the importance of determining relationships before establishing primary keys in the design sequence. What do you see as the primary advantage of using big data analytics - understanding the environment or influencing the environment? Why? 2. Explain...
The SQL uses some operators to throw queries like SELECT uses to selects a data value and shown on the output screen, Where uses for conditions, Group by uses to group the output, Joins uses to join the two or more tables with the ...