It's the first time that the programmer interview pays so much attention to the concept of investigation

Does the programmer interview pay so much attention to the concept of investigation ？

A friend is a programmer , do java Developed , Have more than two years of development experience , Coordinates Guangzhou .
Once I applied for a software development position in a software company in Keyun road information port .

The interviewer gave him a written test , Two of them are like this ：
1.DDL、DML What is the full name , What's the difference between the two ？
2.MYSQL in delete and drop What's the difference? ？

I feel that such written test questions are too basic , It's OK to investigate the newly graduated job seekers , If you have work experience , It doesn't make much sense , It's better to use this time to ask more about the candidate's project experience .

For these two questions , Maybe I can't remember for a while , Let's summarize briefly .

DDL（data definition language） Data definition language , User definition and management sql The language of all objects in the database .

The main command ：create、alter、drop etc.

DML（data manipulation language） Data operation language .
The main command ：select、update、insert、delete etc.

drop The command is mainly used to delete data structures , Including internal data content .（drop database database_name;drop table table_name）

delete The command is mainly used to delete data contents , Do not delete data structure .（delete Field name from Table name where Conditions ）

have access to delete Command to execute rollback operation , Because it uses buffers , The corresponding... Is triggered during execution trigger; But in the use of drop Cannot operate rollback in case of command , Not triggered during operation trigger.

because delete The command does not delete the table , So it doesn't free up any space ; and drop The command will delete the entire table , To free up memory space .

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