mysql语句中使用like后面的%(百分号)的问题

   问题:mysql语句中使用like后面的%(百分号) 是不是越多执行效率越慢!

  总用时:0.0489秒 0.0691 0.0485 0.0467

  SELECT `goods_name`, `goods_img`, `sku_id`, `import` FROM
`goods` WHERE `goods_name` LIKE ‘%iPhone%iPod%’ AND `stime` <
1413877244 AND `etime` > 1413877244 ORDER BY `flag` DESC

  总用时:0.0460秒 0.0430 0.0493 0.0783 0.0496

  SELECT `goods_name`, `goods_img`, `sku_id`, `import` FROM
`goods` WHERE `goods_name` LIKE ‘%iPhone%’ AND `goods_name` LIKE
‘%iPod%’ AND `stime` < 1413877367 AND `etime` > 1413877367
ORDER BY `flag` DESC

  总用时:0.0458秒 0.0441秒 0.0449秒

  SELECT `goods_name`, `goods_img`, `sku_id`, `import` FROM
`goods` WHERE `goods_name` LIKE
‘%%%%%%%%%%%%%%%%%%%%%%%iPhone%iPod%%%%%%%%%%%%%%%%%%%%%%%’ AND
`stime` < 1413877997 AND `etime` > 1413877997 ORDER BY
`flag` DESC

  实践证明,百分号的数量不影响sql执行的速度。这几种方法的效率都是差不多的。

  以上是我测试的结果。个人可根据自己的实际需求去选择写法!建议是最好选择第二种!

问题:mysql语句中使用like后面的%(百分号) 是不是越多执行效率越慢!
总用时:0.0489秒 0.0691 0….

mysql常用语句练习-基于ecshop2.7.3数据库(1),mysqlecshop2.7.3

SELECT * FROM ecs_goods WHERE goods_id = 1;
SELECT goods_id, goods_name FROM ecs_goods WHERE goods_id = 1;
SELECT goods_id,cat_id,goods_name FROM ecs_goods WHERE cat_id !=
3;
SELECT goods_id,cat_id,goods_name FROM ecs_goods WHERE cat_id
<> 3;
SELECT goods_id,cat_id,goods_name,shop_price FROM ecs_goods WHERE
shop_price > 3000;
SELECT goods_id,cat_id,goods_name,shop_price FROM ecs_goods WHERE
shop_price <= 100;

SELECT goods_id,cat_id,goods_name,shop_price FROM ecs_goods WHERE
cat_id = 4 OR cat_id = 3;
SELECT goods_id,cat_id,goods_name,shop_price FROM ecs_goods WHERE
cat_id IN( 3, 4 );

SELECT goods_id,cat_id,goods_name,shop_price FROM ecs_goods WHERE
shop_price BETWEEN 100 AND 858;

SELECT goods_id,cat_id,goods_name,shop_price FROM ecs_goods WHERE
cat_id != 3 AND cat_id != 4
SELECT goods_id,cat_id,goods_name,shop_price FROM ecs_goods WHERE
cat_id NOT IN( 3, 4 );
SELECT goods_id,cat_id,goods_name,shop_price FROM ecs_goods WHERE
cat_id NOT BETWEEN 3 AND 4

SELECT goods_id,cat_id,goods_name,shop_price FROM ecs_goods WHERE (
shop_price > 100 AND shop_price < 300 )
OR ( shop_price > 1000 AND shop_price < 3000 );

SELECT goods_id,cat_id,goods_name,shop_price,click_count FROM
ecs_goods WHERE (cat_id = 3 ) AND ( shop_price >= 1000 AND
shop_price <= 3000 )
AND ( click_count > 5 )

 

SELECT * FROM ecs_goods WHERE cat_id IN ( 2, 3, 4, 5 )

SELECT goods_id,cat_id,goods_name FROM ecs_goods WHERE goods_name
LIKE ‘诺基亚%’

 

 #把表中字段num取值范围为20~29之间的值变成20【注:ecshop2.7.3没有这个ecs_mian1这个表,可以自己创建一个,他就一个字段num,
int类型,然后填充一些测试数据】

UPDATE ecs_mian1 SET num = ( FLOOR( num / 10 ) * 10 ) WHERE num >=
20 AND num <= 29

 #把表中字段num取值范围为30~39之间的值变成30

UPDATE ecs_mian1 SET num = ( FLOOR( num / 10 ) * 10 ) WHERE num
BETWEEN 30 AND 39

 

#以”诺基亚”开头的商品

SELECT goods_id, goods_name FROM ecs_goods WHERE goods_name LIKE
‘诺基亚%’;

#截取”诺基亚”后面的商品名称,并用”小米”开始 连接起来
SELECT goods_id, CONCAT( ‘小米’, SUBSTRING( goods_name, 4 ) ) FROM
ecs_goods WHERE goods_name LIKE ‘诺基亚%’;

#截取”诺基亚”后面的商品名称,并用”小米”开始 连接起来后更新
UPDATE ecs_goods SET goods_name = CONCAT( ‘小米’, SUBSTRING(
goods_name, 4 ) ) WHERE goods_name LIKE ‘诺基亚%’

#以上面的语句相反
UPDATE ecs_goods SET goods_name = CONCAT( ‘诺基亚’, SUBSTRING(
goods_name, 4 ) ) WHERE goods_name LIKE ‘小米%’

 

关于NULL:

SELECT NULL = NULL
SELECT NULL != NULL

#建表
CREATE TABLE ghost_user_info(
id INT( 3 ),
user_name VARCHAR( 20 )
)CHARSET utf8 ENGINE MYISAM;

#插入测试数据
INSERT INTO ghost_user_info VALUES( 1, ‘张三’ );
INSERT INTO ghost_user_info VALUES( 2, NULL );

#user_name不等于NULL的记录,不能这样写
SELECT * FROM ghost_user_info WHERE user_name != NULL

#user_name不等于NULL的记录,应该这样写
SELECT * FROM ghost_user_info WHERE user_name IS NOT NULL

#同样的,等于NULL的记录应该是 IS NULL而不是 = NULL
SELECT * FROM ghost_user_info WHERE user_name = NULL
SELECT * FROM ghost_user_info WHERE user_name IS NULL

 #统计函数

SELECT AVG( shop_price ) FROM ecs_goods;
SELECT MAX( shop_price ) FROM ecs_goods;
SELECT MIN( shop_price ) FROM ecs_goods;
SELECT COUNT(*) FROM ecs_goods;
SELECT SUM( shop_price ) / COUNT(*) FROM ecs_goods;

#积压货款
SELECT SUM( shop_price * goods_number ) FROM ecs_goods;

 #统计每个分类的商品平均价格,
group比较耗费资源(先按cat_id排序,再统计)

SELECT cat_id,AVG( shop_price ) FROM ecs_goods GROUP BY cat_id;

#查询每个分类下,商品的数量
SELECT cat_id, COUNT(*) FROM ecs_goods GROUP BY cat_id;

#每个分类下最贵的产品
SELECT cat_id, MAX(shop_price) FROM ecs_goods GROUP BY cat_id;

 

#本店价格比市场价格小200以上的商品
SELECT goods_id, goods_name, market_price – shop_price FROM
ecs_goods WHERE market_price – shop_price > 200

#下面的语句,报错(Unknown column ‘discount_price’ in ‘where clause’
),discount_price这个别名是结果集中(存在内存中)的,where后面的字段需要是磁盘表中的字段

SELECT goods_id, goods_name, ( market_price – shop_price ) AS
discount_price FROM ecs_goods WHERE discount_price > 200

#可以用having关键字过滤查询出来的结果集
SELECT goods_id, goods_name, ( market_price – shop_price ) AS
discount_price FROM ecs_goods WHERE 1 HAVING discount_price > 200

#多列排序

SELECT goods_id, cat_id, goods_name, shop_price FROM ecs_goods
ORDER BY cat_id ASC, shop_price DESC;

 

#查询最新的商品1
SELECT goods_id, goods_name, cat_id FROM ecs_goods ORDER BY
goods_id DESC LIMIT 0,1
#下面两句组合,等于后面的where子查询
SELECT goods_Id, goods_name,cat_id FROM ecs_goods WHERE goods_id =
32
SELECT MAX( goods_id ) FROM ecs_goods;
#(where子查询)查询最新的商品2
SELECT goods_Id, goods_name,cat_id FROM ecs_goods WHERE goods_id =
( SELECT MAX( goods_id ) FROM ecs_goods );

 

#from子查询:每一个分类下,最大的产品id( 最新的产品 )
SELECT goods_id, goods_name, cat_id FROM ecs_goods ORDER BY cat_id
ASC, goods_id DESC
#把上面的语句 当前一个临时的表,放在from后面 组成一个from子查询
SELECT goods_id, goods_name, cat_id FROM ( SELECT goods_id,
goods_name, cat_id FROM ecs_goods ORDER BY cat_id ASC, goods_id
DESC ) AS tmp GROUP BY cat_id

 

#查询有商品的分类

SELECT * FROM ecs_category c WHERE EXISTS( SELECT * FROM ecs_goods g
WHERE g.cat_id = c.cat_id );

 #查询没有商品的分类

SELECT \ FROM ecs_category c WHERE not EXISTS( SELECT * FROM
ecs_goods g WHERE g.cat_id = c.cat_id );*

 

参考:

MySQL EXISTS 和 NOT EXISTS 子查询语法如下:
  • SELECT … FROM table WHERE EXISTS (subquery)

该语法可以理解为:将主查询的数据,放到子查询中做条件验证,根据验证结果(TRUE
或 FALSE)来决定主查询的数据结果是否得以保留。

 

 

#查出主队与客队在2016-06-01~2016-07-01的名称以及比赛结果

create table m(
     mid int,
     hid int,
     gid int,
     mres varchar(10),
     matime date
)engine myisam charset utf8;

create table t (
     tid int,
     tname varchar(20)
)engine myisam charset utf8;


insert into m
     values
     (1,1,2,'2:0','2006-05-21'),
     (2,2,3,'1:2','2006-06-21'),
     (3,3,1,'2:5','2006-06-25'),
     (4,2,1,'3:2','2006-07-21');


insert into t
     values
     (1,'国安'),
     (2,'申花'),
     (3,'布尔联队');

SELECT m.*, t1.`tname`, t2.`tname` FROM m INNER JOIN t AS t1
ON m.`hid` = t1.`tid` INNER JOIN t AS t2 ON m.`gid` = t2.`tid`
WHERE m.`matime` BETWEEN '2006-06-01' AND '2006-07-01'

 

SELECT * FROM ecs_goods WHERE goods_id = 1; SELECT goods_id,
goods_name FROM ecs_goods WHERE goods_id = 1;…

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