发布于 2017-05-29 21:55:15 | 100 次阅读 | 评论: 0 | 来源: 网友投递

这里有新鲜出炉的Mysql教程,程序狗速度看过来!

Mysql关系型数据库管理系统

MySQL是一个开放源码的小型关联式数据库管理系统,开发者为瑞典MySQL AB公司。MySQL被广泛地应用在Internet上的中小型网站中。由于其体积小、速度快、总体拥有成本低,尤其是开放源码这一特点,许多中小型网站为了降低网站总体拥有成本而选择了MySQL作为网站数据库。


这篇文章主要介绍了MySQL使用变量实现各种排序,需要的朋友可以参考下

核心代码


--下面我演示下MySQL中的排序列的实现
--测试数据
CREATE TABLE tb
(
score INT
);
INSERT tb SELECT 
5 UNION ALL SELECT 
4 UNION ALL SELECT 
4 UNION ALL SELECT 
4 UNION ALL SELECT 
3 UNION ALL SELECT 
2 UNION ALL SELECT
1;
--1.row_number式的排序
SET @row_number =0;
SELECT @row_number := @row_number+1 AS row_number,score 
FROM tb 
ORDER BY score DESC ;
+------------+-------+
| row_number | score |
+------------+-------+
|     1 |   5 |
|     2 |   4 |
|     3 |   4 |
|     4 |   4 |
|     5 |   3 |
|     6 |   2 |
|     7 |   1 |
+------------+-------+
--2.dense_rank式的排序
SET @dense_rank = 0,@prev_score = NULL;
SELECT @dense_rank :=IF(@prev_score=score,@dense_rank,@dense_rank+1) AS decnse_rank,
  @prev_score := score AS score 
FROM tb 
ORDER BY score DESC ; 
+-------------+-------+
| decnse_rank | score |
+-------------+-------+
|      1 |   5 |
|      2 |   4 |
|      2 |   4 |
|      2 |   4 |
|      3 |   3 |
|      4 |   2 |
|      5 |   1 |
+-------------+-------+
--3.rank式的排序
SET @row=0,@rank=0,@prev_score=NULL;
SELECT @row:=@row+1 AS ROW,
    @rank:=IF(@prev_score=score,@rank,@row) AS rank,
    @prev_score:=score AS score
FROM tb 
ORDER BY score DESC;
+------+------+-------+
| ROW | rank | score |
+------+------+-------+
|  1 |  1 |   5 |
|  2 |  2 |   4 |
|  3 |  2 |   4 |
|  4 |  2 |   4 |
|  5 |  5 |   3 |
|  6 |  6 |   2 |
|  7 |  7 |   1 |
+------+------+-------+



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