基础篇
//查询时间,友好提示
$sql = "select date_format(create_time, ‘%Y-%m-%d‘) as day from table_name";
//int 时间戳类型
$sql = "select from_unixtime(create_time, ‘%Y-%m-%d‘) as day from table_name";
//一个sql返回多个总数
$sql = "select count(*) all, " ;
$sql .= " count(case when status = 1 then status end) status_1_num, ";
$sql .= " count(case when status = 2 then status end) status_2_num ";
$sql .= " from table_name";
//Update Join / Delete Join
$sql = "update table_name_1 ";
$sql .= " inner join table_name_2 on table_name_1.id = table_name_2.uid ";
$sql .= " inner join table_name_3 on table_name_3.id = table_name_1.tid ";
$sql .= " set *** = *** ";
$sql .= " where *** ";
//delete join 同上。
//替换某字段的内容的语句
$sql = "update table_name set content = REPLACE(content, ‘aaa‘, ‘bbb‘) ";
$sql .= " where (content like ‘%aaa%‘)";
//获取表中某字段包含某字符串的数据
$sql = "SELECT * FROM `表名` WHERE LOCATE(‘关键字‘, 字段名) ";
//获取字段中的前4位
$sql = "SELECT SUBSTRING(字段名,1,4) FROM 表名 ";
//查找表中多余的重复记录
//单个字段
$sql = "select * from 表名 where 字段名 in ";
$sql .= "(select 字段名 from 表名 group by 字段名 having count(字段名) > 1 )";
//多个字段
$sql = "select * from 表名 别名 where (别名.字段1,别名.字段2) in ";
$sql .= "(select 字段1,字段2 from 表名 group by 字段1,字段2 having count(*) > 1 )";
//删除表中多余的重复记录(留id最小)
//单个字段
$sql = "delete from 表名 where 字段名 in ";
$sql .= "(select 字段名 from 表名 group by 字段名 having count(字段名) > 1) ";
$sql .= "and 主键ID not in ";
$sql .= "(select min(主键ID) from 表名 group by 字段名 having count(字段名 )>1) ";
//多个字段
$sql = "delete from 表名 别名 where (别名.字段1,别名.字段2) in ";
$sql .= "(select 字段1,字段2 from 表名 group by 字段1,字段2 having count(*) > 1) ";
$sql .= "and 主键ID not in ";
$sql .= "(select min(主键ID) from 表名 group by 字段1,字段2 having count(*)>1) ";
业务篇
- 连续范围问题
//创建测试表
CREATE TABLE `test_number` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`number` int(11) unsigned NOT NULL DEFAULT ‘0‘ COMMENT ‘数字‘,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8
//创建测试数据
insert into test_number values(1,1);
insert into test_number values(2,2);
insert into test_number values(3,3);
insert into test_number values(4,5);
insert into test_number values(5,7);
insert into test_number values(6,8);
insert into test_number values(7,10);
insert into test_number values(8,11);
实验目标:求数字的连续范围。
根据上面的数据,应该得到的范围。
1-3
5-5
7-8
10-11
//执行Sql
select min(number) start_range,max(number) end_range
from
(
select number,rn,number-rn diff from
(
select number,@number:[email protected]+1 rn from test_number,(select @number:=0) as number
) b
) c group by diff;