feat: 更新 Mysql 示例

2023-06-27 23:11:19 +08:00 · 2023-06-27 23:11:19 +08:00 · d9253230f0
parent 651a6dbac0
commit d9253230f0
6 changed files with 180 additions and 33 deletions
--- a/codes/mysql/SQL必知必会示例/README.md
+++ b/codes/mysql/SQL必知必会示例/README.md
@ -1,3 +1,3 @@
 # 源码说明

-> 本目录代码为 [《SQL 必知必会》](https://item.jd.com/11232698.html) 部分示例源码
+> 本目录代码为 [《SQL 必知必会》](https://book.douban.com/subject/35167240/) 部分示例源码
--- a/codes/mysql/SQL必知必会示例/select.sql
+++ b/codes/mysql/SQL必知必会示例/select.sql
@ -1,8 +1,8 @@
-/**
- * Mysql 查询示例
- * @author Zhang Peng
- * @date 2018/5/5
- */
+-- --------------------------------------------------------------------------------------
+-- Mysql 查询示例
+-- @author Zhang Peng
+-- @date 2018/5/5
+-- ----------------------------------------------------------------------------------------

 -- -------------------------------------------
 -- 查询数据
@ -24,7 +24,7 @@ FROM products;
 SELECT DISTINCT vend_id
 FROM products;

-- 限制结果
+-- 限制查询数量
 -- 返回前 5 行（1）
 SELECT *
 FROM products
--- a/codes/mysql/SQL性能优化/SQL函数影响索引.sql
+++ b/codes/mysql/SQL性能优化/SQL函数影响索引.sql
@ -0,0 +1,119 @@
+-- --------------------------------------------------------------------------------------
+-- 函数操作影响索引效率示例
+-- @author Zhang Peng
+-- ----------------------------------------------------------------------------------------
+
+-- 步骤 1、建表
+CREATE TABLE tradelog (
+    id         INT(11) UNSIGNED NOT NULL AUTO_INCREMENT COMMENT 'Id',
+    tradeid    VARCHAR(32) DEFAULT NULL,
+    operator   INT(11)     DEFAULT NULL,
+    t_modified DATETIME    DEFAULT NULL,
+    PRIMARY KEY (id),
+    KEY tradeid(tradeid),
+    KEY t_modified(t_modified)
+)
+    ENGINE = InnoDB
+    DEFAULT CHARSET = utf8mb4;
+
+CREATE TABLE trade_detail (
+    id         INT(11) NOT NULL,
+    tradeid    VARCHAR(32) DEFAULT NULL,
+    trade_step INT(11)     DEFAULT NULL, /* 操作步骤 */
+    step_info  VARCHAR(32) DEFAULT NULL, /* 步骤信息 */
+    PRIMARY KEY (id),
+    KEY tradeid(tradeid)
+)
+    ENGINE = InnoDB
+    DEFAULT CHARSET = utf8;
+
+-- 步骤 2、存储过程初始化数据
+
+INSERT INTO trade_detail
+VALUES (1, 'aaaaaaaa', 1, 'add');
+INSERT INTO trade_detail
+VALUES (2, 'aaaaaaaa', 2, 'update');
+INSERT INTO trade_detail
+VALUES (3, 'aaaaaaaa', 3, 'commit');
+INSERT INTO trade_detail
+VALUES (4, 'aaaaaaab', 1, 'add');
+INSERT INTO trade_detail
+VALUES (5, 'aaaaaaab', 2, 'update');
+INSERT INTO trade_detail
+VALUES (6, 'aaaaaaab', 3, 'update again');
+INSERT INTO trade_detail
+VALUES (7, 'aaaaaaab', 4, 'commit');
+INSERT INTO trade_detail
+VALUES (8, 'aaaaaaac', 1, 'add');
+INSERT INTO trade_detail
+VALUES (9, 'aaaaaaac', 2, 'update');
+INSERT INTO trade_detail
+VALUES (10, 'aaaaaaac', 3, 'update again');
+INSERT INTO trade_detail
+VALUES (11, 'aaaaaaac', 4, 'commit');
+
+INSERT INTO tradelog
+VALUES (1, 'aaaaaaaa', 1000, now());
+INSERT INTO tradelog
+VALUES (2, 'aaaaaaab', 1000, now());
+INSERT INTO tradelog
+VALUES (3, 'aaaaaaac', 1000, now());
+
+DELIMITER ;;
+DROP PROCEDURE IF EXISTS init;
+CREATE PROCEDURE init()
+BEGIN
+    DECLARE i INT;
+    SET i = 3;
+    WHILE i < 10000
+        DO
+            INSERT INTO tradelog(tradeid, operator, t_modified)
+            VALUES (concat(char(97 + (i DIV 1000)), char(97 + (i % 1000 DIV 100)), char(97 + (i % 100 DIV 10)),
+                           char(97 + (i % 10))), i, now());
+            SET i = i + 1;
+        END WHILE;
+END;;
+DELIMITER ;
+CALL init();
+
+-- 步骤 3、执行计划查看SQL效率
+-- 3.1.1 此 SQL 对索引字段做函数操作，优化器会放弃走树搜索功能，改为全表扫描
+EXPLAIN
+SELECT count(*)
+FROM tradelog
+WHERE month(t_modified) = 7;
+
+-- 3.1.2 SQL 优化
+EXPLAIN
+SELECT count(*)
+FROM tradelog
+WHERE (t_modified >= '2016-7-1' AND t_modified < '2016-8-1') OR
+    (t_modified >= '2017-7-1' AND t_modified < '2017-8-1') OR
+    (t_modified >= '2018-7-1' AND t_modified < '2018-8-1');
+
+-- 3.2.1 此 SQL 对索引字段隐式的使用了转换函数操作，优化器会放弃走树搜索功能，改为全表扫描
+-- 相当于 select * from tradelog where  CAST(tradid AS signed int) = 110717;
+EXPLAIN
+SELECT *
+FROM tradelog
+WHERE tradeid = 110717;
+
+-- 3.3.1 下面两条 SQL 的扫描行数不同
+-- 原因是：字符集 utf8mb4 是 utf8 的超集，所以当这两个类型的字符串在做比较的时候，
+-- MySQL 内部的操作是，先把 utf8 字符串转成 utf8mb4 字符集，再做比较。
+# 需要做字符编码转换
+EXPLAIN
+SELECT d.*
+FROM tradelog l, trade_detail d
+WHERE d.tradeid = l.tradeid AND l.id = 2;
+
+# 上面的 SQL 等价于这条注掉的 SQL
+# SELECT *
+# FROM trade_detail
+# WHERE CONVERT(traideid USING utf8mb4) = $l2.tradeid.value;
+
+# 不需要做字符编码转换
+EXPLAIN
+SELECT l.operator
+FROM tradelog l, trade_detail d
+WHERE d.tradeid = l.tradeid AND d.id = 2;
--- a/codes/mysql/SQL性能优化/等MDL锁.sql
+++ b/codes/mysql/SQL性能优化/等MDL锁.sql
@ -0,0 +1,27 @@
+-- --------------------------------------------------------------------------------------
+-- 函数操作影响索引效率示例
+-- @author Zhang Peng
+-- ----------------------------------------------------------------------------------------
+
+CREATE TABLE t (
+    id INT(11) NOT NULL AUTO_INCREMENT COMMENT 'Id',
+    c  INT(11) DEFAULT NULL,
+    PRIMARY KEY (id)
+)
+    ENGINE = InnoDB;
+
+DELIMITER ;;
+DROP PROCEDURE IF EXISTS init;
+CREATE PROCEDURE init()
+BEGIN
+    DECLARE i INT;
+    SET i = 1;
+    WHILE(i <= 100000)
+        DO
+            INSERT INTO t VALUES (i, i);
+            SET i = i + 1;
+        END WHILE;
+END;;
+DELIMITER ;
+
+CALL init();
--- a/codes/mysql/基本DDL示例.sql
+++ b/codes/mysql/基本DDL示例.sql
@ -7,7 +7,7 @@

 -- --------------------------------------------------------------------- 数据库定义

-- 撤销数据库 test
+-- 删除数据库 db_tutorial
 DROP DATABASE IF EXISTS db_tutorial;

 -- 创建数据库 db_tutorial
@ -18,11 +18,11 @@ USE db_tutorial;

 -- --------------------------------------------------------------------- 数据表定义

-- 撤销表 user
+-- 删除数据表 user
 DROP TABLE IF EXISTS user;
 DROP TABLE IF EXISTS vip_user;

-- 创建表 user
+-- 创建数据表 user
 CREATE TABLE user (
    id       INT(10) UNSIGNED NOT NULL COMMENT 'Id',
    username VARCHAR(64)      NOT NULL DEFAULT 'default' COMMENT '用户名',
@ -43,25 +43,26 @@ ALTER TABLE user
 ALTER TABLE user
 MODIFY COLUMN age TINYINT;

-- 撤销列 age
+-- 删除列 age
 ALTER TABLE user
 DROP COLUMN age;

 -- --------------------------------------------------------------------- 索引定义

-- 创建表 user 的索引 user_index
-CREATE INDEX user_index
-    ON user(id);
+-- 创建表的索引
+CREATE INDEX idx_email
+    ON user(email);

-- 创建表 user 的唯一索引 user_index2
-CREATE UNIQUE INDEX user_index2
-    ON user(id);
+-- 创建表的唯一索引
+CREATE UNIQUE INDEX uniq_username
+    ON user(username);

-- 撤销表 user 的索引
+-- 删除表 user 的索引
 ALTER TABLE user
-    DROP INDEX user_index;
+DROP INDEX idx_email;
+
 ALTER TABLE user
-    DROP INDEX user_index2;
+DROP INDEX uniq_username;

 -- --------------------------------------------------------------------- 视图定义

@ -71,5 +72,5 @@ SELECT id, username
 FROM user
 WHERE id < 10;

-- 撤销表 user 的视图 top_10_user_view
+-- 删除表 user 的视图 top_10_user_view
 DROP VIEW top_10_user_view;