[MongoDB] The high query operation of MongoDB (III), mongodboperation

[MongoDB] The high query operation of MongoDB (III), mongodboperation
1, Sort

Needless to say, mongodb also support to sort data. THe positive one means sorting by asc order and negetive means by desc.

2. Group

The grammar of group:

Description Of Argument:

Key: The field need to group

Cond: query condition

Initial: initialize the counter of group

Redue: generally statistic operation

Finalize: further operation after group, for exampe calcuate the average.

3.

3. Distinct

It's the same as the distinct in the relational database.

4. page

The mongodb supports to use skip and limit to query by page.

5. Cursors and Cursor Methods

6. $ query/$ orderby/$ explain

[MongoDB] how to stop a MongoDB Server

If the server runs on the terminal as a foreground process, press Ctrl-C. Otherwise, use the kill command to send a signal. If the PID of mongod is 10014, you can use kill-2 10014 (SIGINT) or kill 10014 (SIGTERM ).
When mongod receives the SIGINT or SIGTERM, it exits. That is to say, it will wait until the current operation or file pre-distribution is completed (it takes some time), close all open connections, refresh the cached data to the disk, and finally stop. Do not send SIGKILL (kill-9) to a running MongoDB instance ). This will cause the database to be shut down directly, and the previous steps will be ignored, which will damage the data file.
 
What sort of data is inserted into mongodb? Why are the first three inserted in sequence? The fourth article is not.

Is stored in the order of file space Storage