MySQL函数使用记录

1、CONCAT and COALESCE

• CONCAT(field1, field2, ...): 如果其中一个field是null，则返回null。returns NULL if any argument is NULL
• COALESCE(value,...):Returns the first non-NULL value in the list, or NULL if there are no non-NULL values.

select distinct `doc`.* from `wk_project` as `pro` left join `wk_document` as `doc` on `pro`.`project_id` = `doc`.`project_id` and `pro`.`project_id` = '1' where CONCAT(doc.doc_name, COALESCE(doc.doc_content,'')) LIKE '%员工%' order by `doc`.`doc_sort` asc, `doc`.`doc_id` asc

2、length and char_length

select length('日本語'), char_length('日本語'); // 9 3

3、FIND_IN_SET

字段poster_category_id是存储类似于1,2,56,48的信息段，需要搜索包含48字段的时候

select * from posters where FIND_IN_SET('48', poster_category_id);