问题：Unknown column ‘明信片‘ in ‘where clause‘

错错误代码如下

Exception in thread "main" java.sql.SQLSyntaxErrorException: Unknown column '明信片' in 'where clause'
	at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:120)
	at com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:122)
	at com.mysql.cj.jdbc.StatementImpl.executeQuery(StatementImpl.java:1201)
	at com.example.myapplication.dao.productDao.getProductByCategory(productDao.kt:15)
	at com.example.myapplication.KotlintestKt.main(kotlintest.kt:15)
	at com.example.myapplication.KotlintestKt.main(kotlintest.kt)

Process finished with exit code 1

原因：sql语句中传入参数为中文，需要加个单引号。

错误示例：

val sql = "select * from product where category = $category"

正确示例：

val sql = "select * from product where category = '$category'"