qq_43813182的博客

connect函数用法：CONCAT(str1,str2,…)返回结果为连接参数产生的字符串。如有任何一个参数为NULL ，则返回值为 NULL。例题： 牛客：SQL32将employees表的所有员工的last_name和first_name拼接起来作为Nameselect concat(last_name," ",first_name) as name from employees ;connect_ws函数用法：CONCAT_WS(separator,str1,str2,…)

题目：牛客SQL29select f.film_id,f.title from film as f left join film_category as fc onf.film_id = fc.film_idleft join category as c onc.category_id = fc.category_idwherec.category_id is null;

子查询，下面的SQL逻辑很清晰。最后用film_id查电影表中的title与descriptionselect title,description from film where film_id IN ( #再用查到的categoryid查询对应关系表中的film_id select film_id from film_category where category_id IN ( #先在分类表中查分类名为Action的category_id sele