示例：
SELECT COL1
FROM TABLE1
ORDER BY CASE WHEN COL1 = 'A' THEN 1 ELSE 2 END,COL1;//COL1为A的排在最前面，剩下的按COL1的值顺序排列
写成这样更清晰：
SELECT COL1,CASE WHEN COL1 = 'A' THEN 1 ELSE 2 END FLAG
FROM TABLE1
ORDER BY FLAG,COL1;
参考：https://bbs.csdn.net/topics/392020241