VARCHAR repeat(VARCHAR str, INT count)
将字符串 str 重复 count 次输出,count 小于1时返回空串,str,count 任一为NULL时,返回 NULL
MySQL > SELECT repeat("a", 3);
+----------------+
| repeat('a', 3) |
+----------------+
| aaa |
+----------------+
MySQL > SELECT repeat("a", -1);
+-----------------+
| repeat('a', -1) |
+-----------------+
| |
+-----------------+
REPEAT,