MySQL 中,不可直接修改数据库名称。有一种变通的方式如下:如果有一个数据库名称是 “old_database”,想把这个数据库的名字改成 “new_database”;首先创建一个新的数据库 “new_database”create database new_database;
获取所有源库的表名use information_schema;
select table_name from TABLES where TABLE_SCHEMA=’old_database’;
然后按照以下命令一个个修改rename table old_database.[tablename] to new_da
SELECT id,title FROM tb_item GROUP BY id
SELECT id,title,count(*) AS counter FROM tb_item GROUP BY id
counter 实际上是每组的计数统计分组后的数据,应该使用这样的子查询:select count(*) from (select count(*) FROM service GROUP BY name,service) t
实例:var replacements = {tags:"11,12,13"}
var sql = `
SELECT id,tags,title,r.*
一、concat()函数concat(str1, str2,...)
将多个字符串连接成一个字符串。返回结果为连接参数产生的字符串,如果有任何一个参数为null,则返回值为null。例子:select concat (id, title, counter) as info from tb_user;
select concat (id, ',', title, ',', counter) as info from tb_user;
二、concat_ws()函数concat_ws(separator, str1, str2, ...)
和concat()一样,将多个字符串连接成一个字符
显示所有重复数据分组SELECT
origin_id
FROM
topk88_product
GROUP BY origin_id
HAVING count(*) 1
删除所有重复DELETE FROM topk88_product
WHERE origin_id IN (
SELECT
origin_id
FROM
topk88_product
GROUP BY origin_id
HAVING count(*) 1
);
提示:You can't specify tar
tags字段是逗号隔开tag id。查询一select
i.id,
i.title,
i.tags,
(select
GROUP_CONCAT(tb_tag.title SEPARATOR ',')
from tb_tag where id in (i.tags)
) as tags_title
from tb_item as i;
结果:查询二select
i.id,
i.title,
i.tags,
(select
GROUP_CONCAT(tb_tag.title SEPARATOR ',')
fro