Mybatis auto generated keys

1. Support AUTO_INCREMENT columns
We can use the useGeneratedKeys and keyProperty attributes to let the database generate the auto_increment column value and set that generated value into one of the input object properties as follows:

 INSERT INTO STUDENTS(NAME, EMAIL, PHONE)
 VALUES(#{name},#{email},#{phone})

Here the STUD_ID column value will be autogenerated by MySQL database, and the generated value will be set to the studId property of the student object. 

2. Don't support AUTO_INCREMENT columns

Some databases such as Oracle don't support AUTO_INCREMENT columns and use SEQUENCE to generate the primary key values.
Assume we have a SEQUENCE called STUD_ID_SEQ to generate the STUD_ID primary key values. Use the following code to generate the primary key:

 
 SELECT ELEARNING.STUD_ID_SEQ.NEXTVAL FROM DUAL
 
 INSERT INTO STUDENTS(STUD_ID,NAME,EMAIL, PHONE)
 VALUES(#{studId},#{name},#{email},#{phone})

Here we used the subelement to generate the primary key value and stored it in the studId property of the Student object. The attribute order="BEFORE" indicates that MyBatis will get the primary key value, that is, the next value from the sequence and store it in the studId property before executing the INSERT query.
We can also set the primary key value using a trigger where we will obtain the next value from the sequence and set it as the primary key column value before executing the INSERT query.
If you are using this approach, the INSERT mapped statement will be as follows:

 INSERT INTO STUDENTS(NAME,EMAIL, PHONE)
 VALUES(#{name},#{email},#{phone})
 
 SELECT ELEARNING.STUD_ID_SEQ.CURRVAL FROM DUAL