sql

（case语法 ：case 开始，end 结束）

        select case when 1=1 then '1等于1' 
                when 1=2 then '1等于2啦'
                when 1=3 then '1=3'
                else '其他等式'
          end

拼接
UNION
UNION ALL

SELECT * FROM 
(SELECT f.`网站` as id, f.`关键词` as gg, f.`标题` as ki, f.url as c FROM (SELECT * FROM google_data LIMIT 10) as f

UNION ALL

SELECT * FROM `ddd` as nn) as fg

有个limit 10 就好用子查询即用括号在查一层 ，否则认为是整张表的limit ,所以就语法报错，（即它理解为
SELECT * FROM  (SELECT f.`网站` as id, f.`关键词` as gg, f.`标题` as ki, f.url as c FROM (SELECT * FROM google_data ) as f
UNION ALL
SELECT * FROM `ddd` as nn) as fg
LIMIT 10
）
上下两张边拼接
例如
   a  b
0  1  2
1  4  6
**************************************************
   a  b
0  1  2
1  4  6
2  5  5
**************************************************

结果：
    a  b
0  1  2
1  4  6
2  5  5
0  1  2
1  4  6

效果为：
上下两张边拼接

Snipaste_2018-10-24_14-36-24.png