CS-Notes/notes/MySQL.md

<!-- GFM-TOC -->
* [?<3F><>????](#?<3F><>????)
    * [1. InnoDB](#1-innodb)
    * [2. MyISAM](#2-myisam)
    * [3. InnoDB ?? MyISAM ????](#3-innodb-??-myisam-????)
* [????????](#????????)
    * [1. ????](#1-????)
    * [2. ??????](#2-??????)
    * [3. ?????](#3-?????)
    * [4. ????????](#4-????????)
* [????](#????)
    * [1. ????????](#1-????????)
        * [1.1 B-Tree ????](#11-b-tree-????)
        * [1.2 ???????](#12-???????)
        * [1.3. ????????????R-Tree??](#13-????????????r-tree??)
        * [1.4 ???????](#14-???????)
    * [2. ?????????](#2-?????????)
    * [3. ???????](#3-???????)
        * [3.1 ????????](#31-????????)
        * [3.2 ??????](#32-??????)
        * [3.3 ????????](#33-????????)
        * [3.4 ?????<3F><>????](#34-?????<3F><>????)
        * [3.5 ???????](#35-???????)
        * [3.6 ????????](#36-????????)
    * [4. B-Tree ?? B+Tree ???](#4-b-tree-??-b+tree-???)
        * [4. 1 B-Tree](#4-1-b-tree)
        * [4.2 B+Tree](#42-b+tree)
        * [4.3 ?????????????? B+Tree](#43-??????????????-b+tree)
        * [4.4 ?????? B-Tree ?? B+Tree](#44-??????-b-tree-??-b+tree)
* [??????????](#??????????)
    * [1. Explain](#1-explain)
    * [2. ??????????](#2-??????????)
    * [3. ??????????](#3-??????????)
    * [4. ????? DELETE ?? INSERT ???](#4-?????-delete-??-insert-???)
* [???????](#???????)
* [?????????????](#?????????????)
    * [1. ???????](#1-???????)
    * [2. ??????](#2-??????)
* [?<3F><>?????](#?<3F><>?????)
<!-- GFM-TOC -->

# ?<3F><>????

## 1. InnoDB

InnoDB ?? MySQL ??????????????<3F><>???????? InnoDB ??????????????????????????<3F><>???<3F><>

???? MVCC ?????????????????????????????????????????????????

?????????????????????????????????????<3F><>?????????

????????????????????????????????????????????????????????<3F><>??? hash ??????????????????????????????????????????????????????????

????<3F><>???????????????????????

## 2. MyISAM

MyISAM ??????????????????????????????????<3F><>????GIS??????? MyISAM ???????????<3F><>?????????????????????????

????????????????????????<3F><>?

????????????????<3F><>??????????????????????????????????????????????<3F><>????????????????????????????

???????????????????<3F><>?

???????? DELAY_KEY_WRITE ??????????????????????????????????????????<3F><>???????????<3F><>??????<3F><>??????????????????????????????????????????????????<3F><>????????????????????????<3F><>?????????????????????????????????????????????????????????

??????????????????????????????????????????????????????? MyISAM ?????

???????????????????<3F><>?????????????????????????????????? MyISAM??

MyISAM ?????????????????<3F><>?????????<3F><>???????????<3F><>?

## 3. InnoDB ?? MyISAM ????

**????**

InnoDB ??????????

**????**

InnoDB ?????????????

**???????**

MyISAM ??????????????? InnoDB ??????????????????????

**????**

MyISAM ??????????? InnoDB ??????<3F><>?????

**????????**

MyISAM ????????????????????????

# ????????

## 1. ????

TINYINT, SMALLINT, MEDIUMINT, INT, BIGINT ?????? 8, 16, 24, 64 <20><>?<3F><>????????????<3F><>??????<3F><>?

INT(11) ?<3F><>????????<3F><>??????????????????????????<3F><>???????????????????

## 2. ??????

FLOAT ?? DOUBLE ??????????DECIMAL ??????<3F><>???????CPU ????????????????????? DECIMAl ??????????? DECIMAL ?????????????????????????

FLOAT??DOUBLE ?? DECIMAL ??????????<3F><>????? DECIMAL(18, 9) ?????? 18 <20><>??? 9 <20><>?<3F><><EFBFBD><EFBFBD>?????????? 9 <20><>?<3F><>?????????

## 3. ?????

????? CHAR ?? VARCHAR ?????????????????????????????

VARCHAR ??????????????????????????<3F><>??????????????????? UPDATE ????????<3F><>??????????????????????????????<3F><>????????<3F><>?????????MyISAM ???<3F><>????????<3F>ě<EFBFBD>???? InnoDB ??????????????<3F><>??????

VARCHAR ??????????<3F><>????? CHAR ???????

## 4. ????????

MySQL ?????????????????????????DATATIME ?? TIMESTAMP??

**DATATIME**

???????? 1001 ?? 9999 ????????????????????? 8 ????<3F><>???

???????????

?????????MySQL ???????????????????????? DATATIME ??????<3F><>2008-01016 22:37:08???????? ANSI ????????????????????????

**TIMESTAMP**

?? UNIX ?????????????? 1970 ?? 1 ?? 1 ????????????????????????????????? 4 ????????????? 1970 ?? ?? 2038 ??

????????<3F><>??

MySQL ???? FROM_UNIXTIME() ?????? Unxi ??????????????????? UNIX_TIMESTAMP() ?????????????? Unix ??????

??????????????????????? TIMESTAMP ?<3F><>?????????????????????

????????? TIMESTAMP????????? DATETIME ???<3F><>??????

# ????

????????<3F><>?????????????????????????????????????<3F><>??????<3F><>?????????????????

???????????????????????????????????

??????<3F><>???????????????????????????????<3F><>???????<3F><>?????????????????<3F><>????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????<3F><>?????????

## 1. ????????

### 1.1 B-Tree ????

B-Tree ?????????? MySQL ?<3F><>?????????????????

???????????????????<3F>k?????????????????????????????????

????????????????????<3F><>?????????<3F><>????????B-Tree ?????????????????????<3F><>?????????????<3F><>?????????????????????????

?????????????????????????????<3F><>

???????????????<3F><>??????<3F><>??????????????????

### 1.2 ???????

????????????????????????

?? MySQL ????? Memory ??????????????????

InnoDB ?????????????????<3F><>????????????????????????????????????????????? B-Tree ???????????????????????????????? B-Tree ???????<3F><>?????????<3F><>??????????????????

?????????????????????????????????<3F><>?????????????????????<3F><>???????????<3F><>???????????????<3F><>??<3F><>???????????????????????????????????????????????????????????????????????????????<3F><>??????????????????????????<3F><>?????

### 1.3. ????????????R-Tree??

MyISAM ?<3F><>??????????????????????????????<3F><>??

??????????????????????????????????<3F><>?????????????????????????

### 1.4 ???????

MyISAM ?<3F><>???????????????????????????<3F><>??????????????????????<3F><>????

??? MATCH AGAINST????????????? WHERE??

## 2. ?????????

- ????????????????????????????

- ??????????????????????????????

- ????? I/O ?????? I/O??

## 3. ???????

### 3.1 ????????

????<3F><>??????????<3F><>?????????????????????????????????????????????????

?????????????????? actor_id ?<3F><>???????

```sql
SELECT actor_id FROM sakila.actor WHERE actor_id + 1 = 5;
```

### 3.2 ??????

???? BLOB??TEXT ?? VARCHAR ??????<3F><>??????????????????????????????????

???????????????????? **?????????** ?????????????????????????????????????????????<3F><>???????????? 1 ???????????????<3F><>???????????????

### 3.3 ????????

??????????????????????<3F><>????????????????????????????????????<3F><>??????????????<3F><>????? actor_id ?? file_id ???????????????

```sql
SELECT file_id, actor_ id FROM sakila.film_actor
WhERE actor_id = 1 OR film_id = 1;
```

### 3.4 ?????<3F><>????

?????????????????<3F><>?????<3F><>????????????????? customer_id ???????? staff_id ???????????? customer_id ?<3F><>??????????????<3F><>

```sql
SELECT COUNT(DISTINCT staff_id)/COUNT(*) AS staff_id_selectivity,
COUNT(DISTINCT customer_id)/COUNT(*) AS customer_id_selectivity,
COUNT(*)
FROM payment;
```

```html
   staff_id_selectivity: 0.0001
customer_id_selectivity: 0.0373
               COUNT(*): 16049
```

### 3.5 ???????

![](https://github.com/CyC2018/InterviewNotes/blob/master/pics/b9e9ae8c-e216-4c01-b267-a50dbeb98fa4.jpg)

????????????????????????????????????<3F><>?????

????????????????<3F><>?????????????<3F><>?????InnoDB ???????????????<3F><>???? B-Tree ???????<3F><>?

?????????????<3F><>???????????????????????????????????????????

**???**

1. ??????????????????????? I/O ??????
2. ???????????? B-Tree ?<3F><>??????????????

**???**

1. ?????????????????? I/O ??????????????????????????????????<3F><>????????????????
2. ???????????????????????????????????????????
3. ????????????????????????????<3F><>???????????<3F><>?<3F><>?
4. ?????????????????<3F><>??<3F><>????????????????????????????<3F><>????????<3F><>?????????????
5. ????<3F><>????<3F>k????????????????????<3F><>?????????????????????????????????????

### 3.6 ????????

??????????????????????<3F><>????

## 4. B-Tree ?? B+Tree ???

### 4. 1 B-Tree

![](https://github.com/CyC2018/InterviewNotes/blob/master/pics/5ed71283-a070-4b21-85ae-f2cbfd6ba6e1.jpg)

??????? B-Tree??????????????????????????? [key, data]??key ?????????data ????????? key ????????

B-Tree ???????????????????????

- ?????????????????????????? B-Tree ???????
- ???????<3F><>? key ????????????<3F><>?
- ?????????????????? key ????? key<sub>i</sub> ?? key<sub>i+1</sub>?????? null?????????????????? key ???? key<sub>i</sub> ??<3F><>?? key<sub>i+1</sub>??

?? B-Tree ?<3F><>? key ?????????????????????????????<3F><>?????????????????????? data????????????????????????????<3F><>????????????????? null ????????????????????????

???????????????????????? B-Tree ????????????????????????????????????????????????????????? B-Tree ?????

### 4.2 B+Tree

![](https://github.com/CyC2018/InterviewNotes/blob/master/pics/63cd5b50-d6d8-4df6-8912-ef4a1dd5ba13.jpg)

?? B-Tree ????B+Tree ??????????

- ??????????????? 2d ?????? 2d+1??
- ?????<3F><> data????<3F><> key????????<3F><>???

### 4.3 ?????????????? B+Tree

![](https://github.com/CyC2018/InterviewNotes/blob/master/pics/1ee5f0a5-b8df-43b9-95ab-c516c54ec797.jpg)

????????????????????????? B+Tree ????????? B+Tree ????????????????????????????????????????????????????????????????????????

### 4.4 ?????? B-Tree ?? B+Tree

?????????????????????????????????????????????????????? B-/+Tree ???????????

???????????<3F><>????????<3F><>?????????????????????????<3F><>?????????????<3F><>????<3F><>????<3F><>???????????????????<3F><>?????<3F><>???? 4k??????????????????<3F><>?????????

?????????????????????????????<3F><>??????<3F><>???????????????????????????<3F><>????????????????? I/O?????????????????????????????<3F><>?????????????????????????????????????????????????????????????????<3F><>?????????????????????<3F><>????????????????????????????????????????????<3F><>?????????????????????????????? I/O ????????????B-Tree ????<3F><>????????? h-1 ?? I/O??????????<3F><>???????????? O(h)=O(logdN)????????????<3F><>????? d ??????????????????? 100????? h ???<3F><>??????????? 3??????????????????h ????????????????????????????????????????????????????????<3F><>??????? B-Tree ????

B+Tree ????????????????????????? d ?<3F><>?????? B+Tree ????????? data ??????????<3F><>??????????<3F><>?????????

# ??????????

## 1. Explain

???????? SQL ???????????<3F><>???????????<3F><>?

- select_type : ?????????<3F><>?????????????????

- key : ????????

- rows : ????????

## 2. ??????????

???????????????????????????????????????????????????????<3F><>?

??<3F><>????? SELECT * ???????????????????<3F><>?

## 3. ??????????

?????? LIMIT ???????????????<3F><>?<3F><>?

????????????????????????????????<3F><>????????????????????????????????????????????<3F>k???????????????ݔ?<3F><>?????????? Explain ???????????? rows ????????????????

```sql
SELECT * FROM sakila.film_actor WHERE film_id = 1;
```

## 4. ????? DELETE ?? INSERT ???

??????????<3F><>???????????????????????????????????????????????????????<3F><>????????????

```sql
DELEFT FROM messages WHERE create < DATE_SUB(NOW(), INTERVAL 3 MONTH);
```
```sql
rows_affected = 0
do {
    rows_affected = do_query(
    "DELETE FROM messages WHERE create  < DATE_SUB(NOW(), INTERVAL 3 MONTH) LIMIT 10000")
} while rows_affected > 0
```

# ???????

**1. ????????????**

????????????????<3F><>????<3F><><EFBFBD><EFBFBD>????<3F><>???????????????????????????????????<3F><>??<3F><>???????<3F><>??????????????????<3F><>???????????????????<3F><>????????????

**2. ??<3F><>??????????**

??????????????????????<3F><>???????????????<3F><>?????????????????????<3F><>????????????????????

**3. ????<3F><>?**

??????????<3F><>??????<3F><>?????????????????????????<3F><>??????????????? payDB?????????? userDB ???????????<3F><>?????????<3F><>??????????<3F><>???

**4. ???<3F><>?**

????<3F><>??????????????<3F><>??????????????<3F><>????<3F><> id ??????????????<3F><>????

**5. ????<3F><>??????<3F><>?????**

?????????<3F><>???????????????????????????????????<3F><>????????

??????????????????????????????????????<3F><>??

**6. ???<3F><>???????**

????????? merge ?<3F><>???<3F><>

**7. ???????????????**

(1) ????????

????<3F><>???????????????<3F><>??????????????????????????????????????????????????????????????????????????????????????????????<3F><>????<3F><>????????<3F><>???????????????????????????????

(2) ?????????????

?????????????????????????????????????????????????????????????????????????????????????????????????<3F><>?????????????????????????????????????????<3F><>????????????????????<3F><>?<3F><>?????<3F><>?

# ?????????????

?????????????<3F><>???????????????????<3F><>???????????????????????????????????????<3F><>?????????????????????????

## 1. ???????

**1.1 ??????????<3F><>????**

??????????????????????????-????????<3F><>?????????????????

**1.2 ???? IP ????? IP ?<3F><>?**

? MySQL ???????????? IP ??????? MySQL ????<3F><>???????? IP ??????????? MySQL ?????????

**1.3 ?<3F><>?????????**

???????????<3F><>????????????????????????

![](https://github.com/CyC2018/InterviewNotes/blob/master/pics/fabd5fa0-b75e-48d0-9e2c-31471945ceb9.jpg)

**1.4 ??????<3F><>?????????**

??????????????????<3F><>???????????????????

## 2. ??????


# ?<3F><>?????

- ?????? MySQL
- [MySQL ????????????????????? ](http://blog.codinglabs.org/articles/theory-of-mysql-index.html)
- [MySQL ???????????? ](http://www.runoob.com/w3cnote/mysql-index.html)
- [20+ ?? MySQL ??????????????? ](https://www.jfox.info/20-tiao-mysql-xing-nen-you-hua-de-zui-jia-jing-yan.html)