From 34ec7ab9e0f24bf55346a80acbe22dbe2a5a16b7 Mon Sep 17 00:00:00 2001 From: pengshiyu <1940607002@qq.com> Date: Sun, 8 May 2022 22:16:17 +0800 Subject: [PATCH] fix --- blog/mysq-advance/mysql-index.md | 420 +++++++++++++++++++++++++++++++ blog/php-mysql/index.md | 2 +- blog/php-mysql/sql-function.md | 13 +- index.html | 35 +++ static/js/prism-python.min.js | 1 + 5 files changed, 468 insertions(+), 3 deletions(-) create mode 100644 static/js/prism-python.min.js diff --git a/blog/mysq-advance/mysql-index.md b/blog/mysq-advance/mysql-index.md index 69e0dae..f80da2f 100644 --- a/blog/mysq-advance/mysql-index.md +++ b/blog/mysq-advance/mysql-index.md @@ -867,3 +867,423 @@ mysql> explain select count(*) from tb_user; 1 row in set, 1 warning (0.00 sec) ``` +索引使用 + + +创建测试表 + +```sql +create table tb_sku( + id int primary key auto_increment, + uuid char(36) +); +``` + +## 6、索引使用 + +### 6.1、验证索引效率 + +生成测试数据（1000万条记录） + +方式一：使用MySQL的自定义函数 + +速度较慢，适合较少的数据 + +```sql +-- 1、定义个生成测试数据的函数 +-- 修改语句结束符 +delimiter $$ + +-- 创建函数 +create function init_data(total int) returns int +begin + -- 声明局部变量 + declare i int default 0; + + -- 循环处理 + while i < total do + -- 生成测试数据 + insert into tb_sku (`uuid`) values (uuid()); + set i = i + 1; + end while; + + -- 返回值 + return i; +end + +-- 结束 +$$ + +-- 修改语句结束符 +delimiter ; + + +-- 2、调用函数生成数据(100W) +mysql> select init_data(1000000); ++--------------------+ +| init_data(1000000) | ++--------------------+ +| 1000000 | ++--------------------+ +1 row in set (1 min 16.08 sec) + +-- 3、删除函数 +drop function init_data; +``` + +方式二： + +使用Python脚本生成，适合生成大量数据 + +```python +# pip install records mysqlclient +import records +import uuid + +db = records.Database('mysql://root:123456@localhost/data?charset=utf8') + +# 100 * 100000 = 1000万条数据 +for i in range(100): + data = [{'uuid': str(uuid.uuid4())} for i in range(100000)] + db.bulk_query("insert into tb_sku(uuid) values(:uuid)", data) + +``` + +```sql +mysql> select count(*) from tb_sku; ++----------+ +| count(*) | ++----------+ +| 10000000 | ++----------+ +1 row in set (0.38 sec) + + +mysql> select * from tb_sku limit 1; ++----+--------------------------------------+ +| id | uuid | ++----+--------------------------------------+ +| 1 | 166fa508-2911-494d-aed2-2a2ee81a2a64 | ++----+--------------------------------------+ +1 row in set (0.00 sec) +``` + + +验证索引效率 +```sql +-- 为建立索引之前，执行如下SQL，查看SQL的耗时 +mysql> select * from tb_sku where uuid = '166fa508-2911-494d-aed2-2a2ee81a2a64'; ++----+--------------------------------------+ +| id | uuid | ++----+--------------------------------------+ +| 1 | 166fa508-2911-494d-aed2-2a2ee81a2a64 | ++----+--------------------------------------+ +1 row in set (2.15 sec) + +-- 创建索引 +mysql> create index idx_sku_uuid on tb_sku (uuid); +Query OK, 0 rows affected (21.85 sec) +Records: 0 Duplicates: 0 Warnings: 0 + +-- 再次执行相同的SQL语句，查看SQL耗时 +mysql> select * from tb_sku where uuid = '166fa508-2911-494d-aed2-2a2ee81a2a64'; ++----+--------------------------------------+ +| id | uuid | ++----+--------------------------------------+ +| 1 | 166fa508-2911-494d-aed2-2a2ee81a2a64 | ++----+--------------------------------------+ +1 row in set (0.01 sec) + +-- 通过主键查询 +mysql> select * from tb_sku where id = 1; ++----+--------------------------------------+ +| id | uuid | ++----+--------------------------------------+ +| 1 | 166fa508-2911-494d-aed2-2a2ee81a2a64 | ++----+--------------------------------------+ +1 row in set (0.00 sec) + +-- 查看执行计划 +mysql> explain select * from tb_sku where uuid = '166fa508-2911-494d-aed2-2a2ee81a2a64'; ++----+-------------+--------+------------+------+---------------+--------------+---------+-------+------+----------+-------------+ +| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | ++----+-------------+--------+------------+------+---------------+--------------+---------+-------+------+----------+-------------+ +| 1 | SIMPLE | tb_sku | NULL | ref | idx_sku_uuid | idx_sku_uuid | 145 | const | 1 | 100.00 | Using index | ++----+-------------+--------+------------+------+---------------+--------------+---------+-------+------+----------+-------------+ +1 row in set, 1 warning (0.00 sec) +``` + + +### 6.2、最左前缀法则 + +如果索引了多列（联合索引），要遵守最左前缀法则。 + +最左前缀法则指的是查询从索引的最左侧列开始，并且不跳过索引中的列。 + +如果跳过某一列，索引将部分失效（后面的字段索引失效） + +```sql +-- 查看表数据 +select * from tb_user; ++----+--------+-------------+------------+------+--------+-------------+ +| id | name | phone | profession | age | status | email | ++----+--------+-------------+------------+------+--------+-------------+ +| 1 | 张飞 | 15210231227 | 美术 | 23 | 1 | 123@qq.com | +| 2 | 关羽 | 15210231297 | 物理 | 24 | 1 | 3339@qq.com | +| 3 | 刘备 | 15214231297 | 数学 | 25 | 0 | 666@qq.com | +| 4 | 孙权 | 15215231297 | 语文 | 20 | 1 | 111@qq.com | ++----+--------+-------------+------------+------+--------+-------------+ +4 rows in set (0.01 sec) + +-- 查看表中的索引 +show index from tb_user; ++---------+------------+--------------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+ +| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment | Visible | Expression | ++---------+------------+--------------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+ +| tb_user | 0 | PRIMARY | 1 | id | A | 4 | NULL | NULL | | BTREE | | | YES | NULL | +| tb_user | 0 | idx_user_phone | 1 | phone | A | 4 | NULL | NULL | YES | BTREE | | | YES | NULL | +| tb_user | 1 | idx_user_name | 1 | name | A | 4 | NULL | NULL | YES | BTREE | | | YES | NULL | +| tb_user | 1 | idx_user_profession_age_status | 1 | profession | A | 4 | NULL | NULL | YES | BTREE | | | YES | NULL | +| tb_user | 1 | idx_user_profession_age_status | 2 | age | A | 4 | NULL | NULL | YES | BTREE | | | YES | NULL | +| tb_user | 1 | idx_user_profession_age_status | 3 | status | A | 4 | NULL | NULL | YES | BTREE | | | YES | NULL | +| tb_user | 1 | idx_user_email | 1 | email | A | 4 | NULL | NULL | YES | BTREE | | | YES | NULL | ++---------+------------+--------------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+ +7 rows in set (0.06 sec) + +-- 查询数据 +select * from tb_user where profession = '美术' and age = 23 and status = 1; ++----+--------+-------------+------------+------+--------+------------+ +| id | name | phone | profession | age | status | email | ++----+--------+-------------+------------+------+--------+------------+ +| 1 | 张飞 | 15210231227 | 美术 | 23 | 1 | 123@qq.com | ++----+--------+-------------+------------+------+--------+------------+ +1 row in set (0.00 sec) + +-- 查看用到的索引:profession、age、status +explain select * from tb_user where profession = '美术' and age = 23 and status = 1; ++----+-------------+---------+------------+------+--------------------------------+--------------------------------+---------+-------------------+------+----------+-------+ +| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | ++----+-------------+---------+------------+------+--------------------------------+--------------------------------+---------+-------------------+------+----------+-------+ +| 1 | SIMPLE | tb_user | NULL | ref | idx_user_profession_age_status | idx_user_profession_age_status | 53 | const,const,const | 1 | 100.00 | NULL | ++----+-------------+---------+------------+------+--------------------------------+--------------------------------+---------+-------------------+------+----------+-------+ +1 row in set, 1 warning (0.00 sec) + +-- 查询profession和age，使用到了索引 +explain select * from tb_user where profession = '美术' and age = 23; ++----+-------------+---------+------------+------+--------------------------------+--------------------------------+---------+-------------+------+----------+-------+ +| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | ++----+-------------+---------+------------+------+--------------------------------+--------------------------------+---------+-------------+------+----------+-------+ +| 1 | SIMPLE | tb_user | NULL | ref | idx_user_profession_age_status | idx_user_profession_age_status | 48 | const,const | 1 | 100.00 | NULL | ++----+-------------+---------+------------+------+--------------------------------+--------------------------------+---------+-------------+------+----------+-------+ +1 row in set, 1 warning (0.00 sec) + +-- 单独查询profession，使用到了索引 +explain select * from tb_user where profession = '美术'; ++----+-------------+---------+------------+------+--------------------------------+--------------------------------+---------+-------+------+----------+-------+ +| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | ++----+-------------+---------+------------+------+--------------------------------+--------------------------------+---------+-------+------+----------+-------+ +| 1 | SIMPLE | tb_user | NULL | ref | idx_user_profession_age_status | idx_user_profession_age_status | 43 | const | 1 | 100.00 | NULL | ++----+-------------+---------+------------+------+--------------------------------+--------------------------------+---------+-------+------+----------+-------+ +1 row in set, 1 warning (0.01 sec) + +-- 查询age和status，没有使用到索引 +explain select * from tb_user where age = 23 and status = 1; ++----+-------------+---------+------------+------+---------------+------+---------+------+------+----------+-------------+ +| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | ++----+-------------+---------+------------+------+---------------+------+---------+------+------+----------+-------------+ +| 1 | SIMPLE | tb_user | NULL | ALL | NULL | NULL | NULL | NULL | 4 | 25.00 | Using where | ++----+-------------+---------+------------+------+---------------+------+---------+------+------+----------+-------------+ +1 row in set, 1 warning (0.01 sec) + +-- 单独查询status，没有使用到索引 +explain select * from tb_user where status = 1; ++----+-------------+---------+------------+------+---------------+------+---------+------+------+----------+-------------+ +| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | ++----+-------------+---------+------------+------+---------------+------+---------+------+------+----------+-------------+ +| 1 | SIMPLE | tb_user | NULL | ALL | NULL | NULL | NULL | NULL | 4 | 25.00 | Using where | ++----+-------------+---------+------------+------+---------------+------+---------+------+------+----------+-------------+ +1 row in set, 1 warning (0.00 sec) + +-- 跳过中间的age字段，只用到了profession，而status没有用到索引 +explain select * from tb_user where profession = '美术' and status = 1; ++----+-------------+---------+------------+------+--------------------------------+--------------------------------+---------+-------+------+----------+-----------------------+ +| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | ++----+-------------+---------+------------+------+--------------------------------+--------------------------------+---------+-------+------+----------+-----------------------+ +| 1 | SIMPLE | tb_user | NULL | ref | idx_user_profession_age_status | idx_user_profession_age_status | 43 | const | 1 | 25.00 | Using index condition | ++----+-------------+---------+------------+------+--------------------------------+--------------------------------+---------+-------+------+----------+-----------------------+ +1 row in set, 1 warning (0.00 sec) + +-- 索引字段可以交换顺序，也能使用到索引 +explain select * from tb_user where age = 23 and status = 1 and profession = '美术'; ++----+-------------+---------+------------+------+--------------------------------+--------------------------------+---------+-------------------+------+----------+-------+ +| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | ++----+-------------+---------+------------+------+--------------------------------+--------------------------------+---------+-------------------+------+----------+-------+ +| 1 | SIMPLE | tb_user | NULL | ref | idx_user_profession_age_status | idx_user_profession_age_status | 53 | const,const,const | 1 | 100.00 | NULL | ++----+-------------+---------+------------+------+--------------------------------+--------------------------------+---------+-------------------+------+----------+-------+ +1 row in set, 1 warning (0.00 sec) +``` + +### 6.3、范围查询 + +联合索引中，出现范围查询（>、<），范围查询右侧的列索引失效 + +```sql +select * from tb_user where profession = '美术' and age > 22 and status = 1; ++----+--------+-------------+------------+------+--------+------------+ +| id | name | phone | profession | age | status | email | ++----+--------+-------------+------------+------+--------+------------+ +| 1 | 张飞 | 15210231227 | 美术 | 23 | 1 | 123@qq.com | ++----+--------+-------------+------------+------+--------+------------+ +1 row in set (0.00 sec) + +-- age使用了大于号>，只有profession和age用到了索引 +explain select * from tb_user where profession = '美术' and age > 22 and status = 1; ++----+-------------+---------+------------+-------+--------------------------------+--------------------------------+---------+------+------+----------+-----------------------+ +| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | ++----+-------------+---------+------------+-------+--------------------------------+--------------------------------+---------+------+------+----------+-----------------------+ +| 1 | SIMPLE | tb_user | NULL | range | idx_user_profession_age_status | idx_user_profession_age_status | 48 | NULL | 1 | 25.00 | Using index condition | ++----+-------------+---------+------------+-------+--------------------------------+--------------------------------+---------+------+------+----------+-----------------------+ +1 row in set, 1 warning (0.01 sec) + +-- 三个字段都用到了索引 +explain select * from tb_user where profession = '美术' and age >= 22 and status = 1; ++----+-------------+---------+------------+-------+--------------------------------+--------------------------------+---------+------+------+----------+-----------------------+ +| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | ++----+-------------+---------+------------+-------+--------------------------------+--------------------------------+---------+------+------+----------+-----------------------+ +| 1 | SIMPLE | tb_user | NULL | range | idx_user_profession_age_status | idx_user_profession_age_status | 53 | NULL | 1 | 25.00 | Using index condition | ++----+-------------+---------+------------+-------+--------------------------------+--------------------------------+---------+------+------+----------+-----------------------+ +1 row in set, 1 warning (0.00 sec) +``` + +## 7、索引失效的场景 + +### 7.1、索引列运算 + +不要在索引列上进行运算操作，否则索引将失效 + +```sql +-- 查看数据 +mysql> select * from tb_user; ++----+--------+-------------+------------+------+--------+-------------+ +| id | name | phone | profession | age | status | email | ++----+--------+-------------+------------+------+--------+-------------+ +| 1 | 张飞 | 15210231227 | 美术 | 23 | 1 | 123@qq.com | +| 2 | 关羽 | 15210231297 | 物理 | 24 | 1 | 3339@qq.com | +| 3 | 刘备 | 15214231297 | 数学 | 25 | 0 | 666@qq.com | +| 4 | 孙权 | 15215231297 | 语文 | 20 | 1 | 111@qq.com | ++----+--------+-------------+------------+------+--------+-------------+ +4 rows in set (0.00 sec) + +-- 查看索引 +mysql> show index from tb_user; ++---------+------------+--------------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+ +| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment | Visible | Expression | ++---------+------------+--------------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+ +| tb_user | 0 | PRIMARY | 1 | id | A | 4 | NULL | NULL | | BTREE | | | YES | NULL | +| tb_user | 0 | idx_user_phone | 1 | phone | A | 4 | NULL | NULL | YES | BTREE | | | YES | NULL | +| tb_user | 1 | idx_user_name | 1 | name | A | 4 | NULL | NULL | YES | BTREE | | | YES | NULL | +| tb_user | 1 | idx_user_profession_age_status | 1 | profession | A | 4 | NULL | NULL | YES | BTREE | | | YES | NULL | +| tb_user | 1 | idx_user_profession_age_status | 2 | age | A | 4 | NULL | NULL | YES | BTREE | | | YES | NULL | +| tb_user | 1 | idx_user_profession_age_status | 3 | status | A | 4 | NULL | NULL | YES | BTREE | | | YES | NULL | +| tb_user | 1 | idx_user_email | 1 | email | A | 4 | NULL | NULL | YES | BTREE | | | YES | NULL | ++---------+------------+--------------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+ +7 rows in set (0.01 sec) + +-- 按照手机号查询数据 +mysql> select * from tb_user where phone = '15210231227'; ++----+--------+-------------+------------+------+--------+------------+ +| id | name | phone | profession | age | status | email | ++----+--------+-------------+------------+------+--------+------------+ +| 1 | 张飞 | 15210231227 | 美术 | 23 | 1 | 123@qq.com | ++----+--------+-------------+------------+------+--------+------------+ +1 row in set (0.00 sec) + +-- 分析索引使用情况 +explain select * from tb_user where phone = '15210231227'; ++----+-------------+---------+------------+-------+----------------+----------------+---------+-------+------+----------+-------+ +| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | ++----+-------------+---------+------------+-------+----------------+----------------+---------+-------+------+----------+-------+ +| 1 | SIMPLE | tb_user | NULL | const | idx_user_phone | idx_user_phone | 47 | const | 1 | 100.00 | NULL | ++----+-------------+---------+------------+-------+----------------+----------------+---------+-------+------+----------+-------+ +1 row in set, 1 warning (0.00 sec) + +-- 查询手机号后两位 +select * from tb_user where substring(phone, 10, 2) = '27'; ++----+--------+-------------+------------+------+--------+------------+ +| id | name | phone | profession | age | status | email | ++----+--------+-------------+------------+------+--------+------------+ +| 1 | 张飞 | 15210231227 | 美术 | 23 | 1 | 123@qq.com | ++----+--------+-------------+------------+------+--------+------------+ +1 row in set (0.00 sec) + +-- 查看执行效率 +explain select * from tb_user where substring(phone, 10, 2) = '27'; ++----+-------------+---------+------------+------+---------------+------+---------+------+------+----------+-------------+ +| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | ++----+-------------+---------+------------+------+---------------+------+---------+------+------+----------+-------------+ +| 1 | SIMPLE | tb_user | NULL | ALL | NULL | NULL | NULL | NULL | 4 | 100.00 | Using where | ++----+-------------+---------+------------+------+---------------+------+---------+------+------+----------+-------------+ +1 row in set, 1 warning (0.01 sec) +``` + +### 7.2、字符串不加引号 + +字符串类型字段使用时，不加引号，索引将失效 + +```sql +-- 字符串查询可以不加引号 +select * from tb_user where phone = 15210231227; ++----+--------+-------------+------------+------+--------+------------+ +| id | name | phone | profession | age | status | email | ++----+--------+-------------+------------+------+--------+------------+ +| 1 | 张飞 | 15210231227 | 美术 | 23 | 1 | 123@qq.com | ++----+--------+-------------+------------+------+--------+------------+ +1 row in set (0.00 sec) + +-- 不加引号的字符串查询没有走索引 +explain select * from tb_user where phone = 15210231227; ++----+-------------+---------+------------+------+----------------+------+---------+------+------+----------+-------------+ +| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | ++----+-------------+---------+------------+------+----------------+------+---------+------+------+----------+-------------+ +| 1 | SIMPLE | tb_user | NULL | ALL | idx_user_phone | NULL | NULL | NULL | 4 | 25.00 | Using where | ++----+-------------+---------+------------+------+----------------+------+---------+------+------+----------+-------------+ +1 row in set, 3 warnings (0.00 sec) +``` + +### 7.3、模糊查询 + +- 如果仅仅是尾部模糊匹配，索引不会失效； +- 如果是头部模糊匹配，索引失效 + +```sql +-- 尾部模糊查询 +select * from tb_user where profession like '美%'; ++----+--------+-------------+------------+------+--------+------------+ +| id | name | phone | profession | age | status | email | ++----+--------+-------------+------------+------+--------+------------+ +| 1 | 张飞 | 15210231227 | 美术 | 23 | 1 | 123@qq.com | ++----+--------+-------------+------------+------+--------+------------+ +1 row in set (0.00 sec) + + +-- 尾部模糊匹配，索引不会失效； +explain select * from tb_user where profession like '美%'; ++----+-------------+---------+------------+-------+--------------------------------+--------------------------------+---------+------+------+----------+-----------------------+ +| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | ++----+-------------+---------+------------+-------+--------------------------------+--------------------------------+---------+------+------+----------+-----------------------+ +| 1 | SIMPLE | tb_user | NULL | range | idx_user_profession_age_status | idx_user_profession_age_status | 43 | NULL | 1 | 100.00 | Using index condition | ++----+-------------+---------+------------+-------+--------------------------------+--------------------------------+---------+------+------+----------+-----------------------+ +1 row in set, 1 warning (0.00 sec) + + +-- 头部模糊匹配，索引失效 +explain select * from tb_user where profession like '%术'; ++----+-------------+---------+------------+------+---------------+------+---------+------+------+----------+-------------+ +| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | ++----+-------------+---------+------------+------+---------------+------+---------+------+------+----------+-------------+ +| 1 | SIMPLE | tb_user | NULL | ALL | NULL | NULL | NULL | NULL | 4 | 25.00 | Using where | ++----+-------------+---------+------------+------+---------------+------+---------+------+------+----------+-------------+ +1 row in set, 1 warning (0.01 sec) +``` + + diff --git a/blog/php-mysql/index.md b/blog/php-mysql/index.md index 005fb3c..94ab4c4 100644 --- a/blog/php-mysql/index.md +++ b/blog/php-mysql/index.md @@ -60,7 +60,7 @@ [流程结构 if while](blog/php-mysql/sql-if-while.md) -[函数 function](blog/php-mysql/sql-function.md) +[内置函数和自定义函数 function](blog/php-mysql/sql-function.md) [存储过程 procedure](blog/php-mysql/sql-procedure.md) diff --git a/blog/php-mysql/sql-function.md b/blog/php-mysql/sql-function.md index e87b18a..e471d17 100644 --- a/blog/php-mysql/sql-function.md +++ b/blog/php-mysql/sql-function.md @@ -1,4 +1,4 @@ -# 函数 function +# 内置函数和自定义函数 function 函数分为两类：系统函数和自定义函数 @@ -19,9 +19,12 @@ length | 判断字符串的字节数,与字符集有关 concat | 连接字符串 insrt | 检查字符是否在目标字符串中，存在返回其位置，不存在返回 0 lcase | 全部小写 -left | 左侧开始截取字符串，直到指定位置 ltrim | 消除左边的空格 +left(str, length) | 左侧开始截取字符串，直到指定位置 +right(str, length) | 右侧开始截取字符串，直到指定位置 mid | 从中间指定位置开始截取，如果不指定截取长度，直接到最后 +`substring(str, index, [length]`) | 从指定位置开始，指定截取长度 +substring_index(str, delim, count) | 按照关键字截取 示例 @@ -39,9 +42,15 @@ select instr('你好中国', '我'); // 0 select lcase('aBcd'); // abcd select left('aBcd', 2); // aB +select right('abcdef', 2); // ef +select substring('abcdef', 2, 3); // bcd +select substring('abcdef', -2, 3); // ef select ltrim(' abc d '); // abc d select mid('你好中国', 3); // 中国 + +select substring_index('www.baidu.com', '.', 2); // www.baidu +select substring_index('www.baidu.com', '.', -2); // baidu.com ``` ### 1.2、时间函数 diff --git a/index.html b/index.html index bc51b94..fa5825b 100644 --- a/index.html +++ b/index.html @@ -18,6 +18,15 @@ href="static/js/vue@4.12.2.min.css"> @@ -85,12 +116,16 @@ + + + + diff --git a/static/js/prism-python.min.js b/static/js/prism-python.min.js new file mode 100644 index 0000000..96932b0 --- /dev/null +++ b/static/js/prism-python.min.js @@ -0,0 +1 @@ +Prism.languages.python={comment:{pattern:/(^|[^\\])#.*/,lookbehind:!0,greedy:!0},"string-interpolation":{pattern:/(?:f|fr|rf)(?:("""|''')[\s\S]*?\1|("|')(?:\\.|(?!\2)[^\\\r\n])*\2)/i,greedy:!0,inside:{interpolation:{pattern:/((?:^|[^{])(?:\{\{)*)\{(?!\{)(?:[^{}]|\{(?!\{)(?:[^{}]|\{(?!\{)(?:[^{}])+\})+\})+\}/,lookbehind:!0,inside:{"format-spec":{pattern:/(:)[^:(){}]+(?=\}$)/,lookbehind:!0},"conversion-option":{pattern:/![sra](?=[:}]$)/,alias:"punctuation"},rest:null}},string:/[\s\S]+/}},"triple-quoted-string":{pattern:/(?:[rub]|br|rb)?("""|''')[\s\S]*?\1/i,greedy:!0,alias:"string"},string:{pattern:/(?:[rub]|br|rb)?("|')(?:\\.|(?!\1)[^\\\r\n])*\1/i,greedy:!0},function:{pattern:/((?:^|\s)def[ \t]+)[a-zA-Z_]\w*(?=\s*\()/g,lookbehind:!0},"class-name":{pattern:/(\bclass\s+)\w+/i,lookbehind:!0},decorator:{pattern:/(^[\t ]*)@\w+(?:\.\w+)*/m,lookbehind:!0,alias:["annotation","punctuation"],inside:{punctuation:/\./}},keyword:/\b(?:_(?=\s*:)|and|as|assert|async|await|break|case|class|continue|def|del|elif|else|except|exec|finally|for|from|global|if|import|in|is|lambda|match|nonlocal|not|or|pass|print|raise|return|try|while|with|yield)\b/,builtin:/\b(?:__import__|abs|all|any|apply|ascii|basestring|bin|bool|buffer|bytearray|bytes|callable|chr|classmethod|cmp|coerce|compile|complex|delattr|dict|dir|divmod|enumerate|eval|execfile|file|filter|float|format|frozenset|getattr|globals|hasattr|hash|help|hex|id|input|int|intern|isinstance|issubclass|iter|len|list|locals|long|map|max|memoryview|min|next|object|oct|open|ord|pow|property|range|raw_input|reduce|reload|repr|reversed|round|set|setattr|slice|sorted|staticmethod|str|sum|super|tuple|type|unichr|unicode|vars|xrange|zip)\b/,boolean:/\b(?:False|None|True)\b/,number:/\b0(?:b(?:_?[01])+|o(?:_?[0-7])+|x(?:_?[a-f0-9])+)\b|(?:\b\d+(?:_\d+)*(?:\.(?:\d+(?:_\d+)*)?)?|\B\.\d+(?:_\d+)*)(?:e[+-]?\d+(?:_\d+)*)?j?(?!\w)/i,operator:/[-+%=]=?|!=|:=|\*\*?=?|\/\/?=?|<[<=>]?|>[=>]?|[&|^~]/,punctuation:/[{}[\];(),.:]/},Prism.languages.python["string-interpolation"].inside.interpolation.inside.rest=Prism.languages.python,Prism.languages.py=Prism.languages.python; \ No newline at end of file -- GitLab