Write down the first version of Understanding TiDB chapter

[tisonkun]

• [x] #56
  • [x] #55
  • [x] #86
  • [x] #87
• [x] #88
• [x] #89
  • [x] #58
  • [x] #59
  • [x] #80
  • [x] #90
  • [ ] #91
• [x] #57
  • [x] #92
  • [ ] #93
  • [x] #94
  • [ ] #95
• [x] #74
  • [x] #150
  • [x] #114
  • [ ] #115
  • [x] #116
  • [x] #117
  • [x] #118
  • [x] #119
• [x] #54
• [x] #53
• [x] #61

[LittleFall]

What is the difference between DDL, DML, DQL chapters here and the corresponding chapters in TiDB documents?

[tisonkun]

@LittleFall I think they share a lot process described in "The Lifecycle of a Statement", but the section focuses on the differnece.

For example, DDL creates tables or drop tables, which updates the metadata which DQL doesn't touch. DQL will have a complex optimization and execution phase.

cc @mjonss @you06 @mengxin9014

[you06]

@tisonkun I created the issues for transaction sections, can you help to assign these issues and add them to the tracing list?

[tisonkun]

@you06 updated.

[tisonkun]

I think the mentioned candidate can comment directly and I'll assign if they ask for it explicitly.