因为name 为字符串类型,MySql 会做隐式的类型转换,做了类型的转换,所以不会去走索引; 10.少用or或in,用它查询时,mysql不一定使用索引,mysql内部优化器会根据检索比例、表大小等多个因素整体评估是否使用索引,详见范围查询优化 EXPLAIN SELECT * FROM employees WHERE name = 'LiLei' or name = 'HanMeimei'; ...
I have been trying to detect hard coded passwords in source code files. Currently I am checking for variable assignments and comparison for identifiers with a sub-string matching with password,pswd. B...how to save jupyter output into a pdf file I am doing some data science analysis on ju...
| Variable_name | Value | +---+---+ | log_slow_admin_statements | OFF | | log_slow_slave_statements | OFF | | slow_launch_time | 2 | | slow_query_log | OFF | | slow_query_log_file | F:\mysql-5.7.25\data\DESKTOP-7TLR5VO-slow.log | +---+---...
5.explain the difference between:a.abstract class and interfaceb.class and object6.What is a package in Java?How we can create a package in Java? Howare packages used? Give an example of one of the standard packages that are part of Java.7.a. Define variable. Write down the syntax ...
I have been trying to detect hard coded passwords in source code files. Currently I am checking for variable assignments and comparison for identifiers with a sub-string matching with password,pswd. B...how to save jupyter output into a pdf file I am doing some data science analysis on ju...
-- of error occurred. In some cases, it can be assigned to the -- poGenStatus variable to be returned to the client. CASE hSqlstate WHEN '02000' THEN --row not found SET poGenStatus=5000; WHEN '42724' THEN --missing llsp
What is shallow copy Explain with an example in Java - Creating an exact copy of an existing object in the memory is known as cloning.The clone() method of the class java.lang.Object accepts an object as a parameter, creates and returns a copy of it (cl
| Variable_name | Value | +---+---+ | Handler_read_first | 1 | | Handler_read_key | 164 | | Handler_read_last | 0 | | Handler_read_next | 107 | | Handler_read_prev | 0 | | Handler_read_rnd | 0 | | Handler_read_rnd_next | 161 ...
error("Variable name: " + decl.getVariableName()); err.error("Line number of reference: " + var.getLocation().getLineNumber() + " in " + var.getLocation().getSystemId()); err.error("Line number of declaration: " + decl.getLocation().getLineNumber() + " in " + decl.getLocation()...
select*fromINFORMATION_SCHEMA.SESSION_STATUSwhereVARIABLE_NAMElike'HANDLER_READ%'andVARIABLE_VALUE<>'0'orderbycast(VARIABLE_VALUEasUNSIGNEDINTEGER)desc; 当从上述表查询数据获取SQL语句读取索引次数时,会导致Handler_read_rnd_next变量值增大;当使用排序时,还会导致Handler_read_rnd变量值增大。因此需要获取SQL语句...