mysql惯用语法sql

查看表列名

SHOW FIELDS from 表名

?查看N条数据

limit  N 

?例如：select * from ?user limit ?50，查询用户表前50条数据

?

查看某列值字符长度大于2的结果

SELECT * FROM zhuce WHERELENGTH(user_yuanyin)>= 2

?length是一个函数，判断字符的长度，>=2 应该写在外面

?

查看某字段的字符长度

SELECT LENGTH(字段名) 

?

?

(YEAR(CURDATE())-YEAR(列名))

SELECT COUNT(personcard_no) AS c, personcard_no FROM eye_refraction_info WHERE del_flag = 0 GROUP BY personcard_no HAVING c = N 

SELECT DISTINCT * FROM  eye_diab_visualacuity   WHERE (ucvaleft BETWEEN 06  and 30)  OR (ucvaright BETWEEN 06  and 30)

DATE_FORMAT(需要格式化的时间字段,'%y-%m_%d')

SELECT *,COUNT(DISTINCT personcard_no) FROM eye_refraction_info GROUP BY personcard_no