MySQL optimization index (the index table optimization case)

1, single-table query optimization

Build SQL table

CREATE TABLE IF NOT EXISTS `article` (
`id` INT(10) UNSIGNED NOT NULL PRIMARY KEY AUTO_INCREMENT,
`author_id` INT(10) UNSIGNED NOT NULL,
`category_id` INT(10) UNSIGNED NOT NULL,
`views` INT(10) UNSIGNED NOT NULL,
`comments` INT(10) UNSIGNED NOT NULL,
`title` VARBINARY(255) NOT NULL,
`content` TEXT NOT NULL
);
 
INSERT INTO `article`(`author_id`, `category_id`, `views`, `comments`, `title`, `content`) VALUES
(1, 1, 1, 1, '1', '1'),
(2, 2, 2, 2, '2', '2'),
(1, 1, 3, 3, '3', '3');
 
SELECT * FROM article;

Case

Case # query category_id greater than 1 to 1 and comments, views most article_id.

Execute sql:

EXPLAIN SELECT id,author_id FROM article WHERE category_id = 1 AND comments > 1 ORDER BY views DESC LIMIT 1;

# Conclusion: Obviously, type is ALL, that is the worst case. Extra Lane also appeared Using filesort, it was the worst of circumstances. Optimization is a must.

Query Index: show index from article;

# Start optimizing: 
# 1.1 New index + Delete Index 
#ALTER TABLE `article` idx_article_ccv the ADD INDEX (` category_id`, `comments`,` views`); the Create index idx_article_ccv ON Article This article was (category_id, Comments, views);
 DROP INDEX idx_article_ccv ON Article This article was

# 1.2 第2次EXPLAIN
EXPLAIN SELECT id,author_id FROM `article` WHERE category_id = 1 AND comments >1 ORDER BY views DESC LIMIT 1;

#结论：
#type 变成了 range,这是可以忍受的。但是 extra 里使用 Using filesort 仍是无法接受的。
#但是我们已经建立了索引,为啥没用呢?
#这是因为按照 BTree 索引的工作原理,
# 先排序 category_id,
# 如果遇到相同的 category_id 则再排序 comments,如果遇到相同的 comments 则再排序 views。
#当 comments 字段在联合索引里处于中间位置时,
#因comments > 1 条件是一个范围值(所谓 range),
#MySQL 无法利用索引再对后面的 views 部分进行检索,即 range 类型查询字段后面的索引无效。

# 1.3 删除第一次建立的索引
DROP INDEX idx_article_ccv ON article;

# 1.4 第2次新建索引
#ALTER TABLE `article` ADD INDEX idx_article_cv ( `category_id` , `views` ) ;
create index idx_article_cv on article(category_id,views);

# 1.5 第3次EXPLAIN
EXPLAIN SELECT id,author_id FROM article WHERE category_id = 1 AND comments > 1 ORDER BY views DESC LIMIT 1;

#结论：可以看到,type 变为了 ref,Extra 中的 Using filesort 也消失了,结果非常理想。

MySQL optimization index (the index table optimization case)

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