Answers for "Caused by: java.sql.SQLSyntaxErrorException: Unknown column 'this_.firstName' in 'field list'"

java.sql.sqlsyntaxerrorexception: unknown column

When this error is reported in the background, it means that the field name 
in the entity class is wrong. Solution:

1. Check whether the field name in the database is consistent with the field 
	name in the entity class, pay special attention to the word letters,

2. Check whether the fields in the database are consistent with the fields 
	in the entity class. For example, if there is no such field in the database, this error will be reported if it appears in the entity class (this is usually the case when the code written by others is changed.)

java.sql.sqlsyntaxerrorexception: unknown column

When this error is reported in the background, it means that the field name 
in the entity class is wrong. Solution:

1. Check whether the field name in the database is consistent with the field 
	name in the entity class, pay special attention to the word letters,

2. Check whether the fields in the database are consistent with the fields 
	in the entity class. For example, if there is no such field in the database, this error will be reported if it appears in the entity class (this is usually the case when the code written by others is changed.)