sql过滤版本号为3位的

SELECT ( SELECT p.NAME FROM project p WHERE p.pid = b.project_id ) AS "项目名称" ,
b.version_num AS "版本" ,if(b.static_check_problem_density is NULL ,"--",b.static_check_problem_density) AS "静态问题密度"
FROM dev_score b WHERE b.static_check_problem_density is NULL and b.date >"2018-12-31" and b.date <"2019-04-01"
and (LENGTH(b.version_num) - LENGTH( REPLACE (b.version_num, '.', ''))) <= 2