drop table tb;
create table tb(id int, value1 varchar(10), value2 varchar(20));
insert into tb values(1,'aa','11');
insert into tb values(1,'bb','22');
insert into tb values(2,'aaa','111');
insert into tb values(2,'bbb','222');
insert into tb values(2,'ccc','333');

 SELECT
    id,stuff(
        (
            SELECT ',' + VALUE1 FROM tb AS t WHERE t.id = tb.id FOR xml path ('')
        ), 1, 1, ''
    ) as VALUE1,
stuff(
        (
            SELECT ',' + VALUE2 FROM tb AS t WHERE t.id = tb.id FOR xml path ('')
        ), 1, 1, ''
    ) as VALUE2
FROM tb GROUP BY id

 select id, group_concat(value1)value1,group_concat(value2)value2 from tb group by id;  

-- 得到两个日期之间相差的月份数，也可以得到相差天数，只需要替换函数中第一个参数，注意各函数参数的取值范围，有兴趣的试下其他的。
1 select DATEDIFF(M,'','');-- sqlserver

 select TIMESTAMPDIFF(MONTH,'','');-- mysql

-- 第二个参数是否包含第一个参数，如果包含返回1，不包含返回0
1 select charindex('a','abcd');-- sqlserver

 select LOCATE('a','abcd');-- mysql

 create table test2 as select * from test1;-- mysql

 select * into test2 from test1;-- sqlserver