sql语句的问题，有人遇到过吗

下面两条sql语句，先执行第一条，查出来的结果复制到第二条sql语句中，就能出现7月4日到7月10日的日期，
第一条语句查询出来的结果集
select 1 union all select 1 union all select 1 union all select 1 union all select 1 union all select 1 union all select 1
可是把第一条sql语句直接放到第二条sql语句中，查询就错了，可能它把结果集当做字符串来处理，能把两条sql直接拼接在一起，查询的结果还是对的吗？

第一条sql
SELECT LEFT(REPEAT(" select 1 union all",-DATEDIFF('2017-07-04','2017-07-10')+1),
LENGTH(REPEAT(" select 1 union all",-DATEDIFF('2017-07-04','2017-07-10')+1))-LENGTH(" union all"))

对的日期
SELECT DATE_ADD('2017-07-04',INTERVAL @i:=@i+1 DAY) as date FROM (
select 1 union all select 1 union all select 1 union all select 1 union all select 1 union all select 1 union all select 1
) as tmp,(SELECT @i:= -1) t

错的日期
SELECT DATE_ADD('2017-07-04',INTERVAL @i:=@i+1 DAY) as date FROM (
SELECT LEFT(REPEAT(" select 1 union all",-DATEDIFF('2017-07-04','2017-07-10')+1),
LENGTH(REPEAT(" select 1 union all",-DATEDIFF('2017-07-04','2017-07-10')+1))-LENGTH(" union all"))
) as tmp,(SELECT @i:= -1) t

代码检查可以忽略，因为不会报错

SELECT LEFT(REPEAT(" select 1 union all",-DATEDIFF('2017-07-04','2017-07-10')+1),
LENGTH(REPEAT(" select 1 union all",-DATEDIFF('2017-07-04','2017-07-10')+1))-LENGTH(" union all"))
上面这一句的结果只是一个字符串sql而已，并不能作为一个结果集，要让他返回结果集你就要预编译sql然后执行，下面是可以正常返回的

 SELECT LEFT(REPEAT(" select 1 union all",-DATEDIFF('2017-07-04','2017-07-10')+1),
LENGTH(REPEAT(" select 1 union all",-DATEDIFF('2017-07-04','2017-07-10')+1))-LENGTH(" union all")) INTO @ss;
SET @result = CONCAT('SELECT DATE_ADD(\'2017-07-04\',INTERVAL @i:=@i+1 DAY) AS DATE FROM (',@ss,') AS tmp,(SELECT @i:= -1) t');
PREPARE stmt FROM @result;
EXECUTE stmt;

不使用预编译可以吗，本来分开写可以的，脑残的kw代码检查说有可能sql注入，才需要改，