Insert and update each database

mysql：

A trite question , Batch insertion occurs in the business , But some data need to be judged whether it exists , If it exists, it will be updated .

So in mysql among , Use on duplicate key update Can achieve this goal ！

About the use of this method , There are many introductions on Baidu , I won't go into that here .

The main purpose is to save the problems encountered in the process of use .

1. Use jdbctemplate To operate the database , So dynamic sql On the spelling of , Note that the field names match , Otherwise, an error will be reported

Unknown column '***' in 'field list'

You can still encounter jdbctemplate A deep pit problem of ,

template.queryForList, This method cannot return list object , Only single column values will be obtained list, For example, a table has ten fields , This will only return all of one field list.. When you use it to return objects , Errors will be reported, such as the following data ：

Incorrect column count: expected 1, actual 10

2. Data table structure , The new time and update time fields are generally available , By default

`create_datetime` timestamp(0) NULL DEFAULT CURRENT_TIMESTAMP(0) COMMENT ' Creation time ',
  `update_datetime` timestamp(0) NULL DEFAULT CURRENT_TIMESTAMP(0) ON UPDATE CURRENT_TIMESTAMP(0) COMMENT ' Update time ',

It will follow the data update to modify the corresponding time .

But combine on duplicate key update When you use it , If all fields are the same and already exist , Then the data will not be updated , Time will not be updated （ The main reason is that duplicate data is operated at that time , The time has not been updated , And scratched his head ..）

DM database ：

DM As a domestic database , Insert and update , And db2 be similar .

  use merge into The way , Take the primary key or index set in the table as the judgment condition , Update other fields , If it is new data, insert . Of course, the sql The definition is rough , It is good to look at , If you are using a predefined sql, May adopt stringbuilder Go to together , Reduce object creation .

And mysql The same thing is that it encounters duplicate data , Will not take the initiative to update , Only when a certain field or some field changes are found, the update operation will be performed .