25，MySQL 8.0参考手册 5.1.10.2时区闰秒支持

闰秒值以时间部分返回，以时间部分结束 :59:59。这意味着NOW()在闰秒期间，一个函数 可以返回相同的值两到三秒。时间部分以时间部分结尾:59:60或被 :59:61认为是无效的字面时间值仍然是事实。

如果有必要TIMESTAMP在闰秒前一秒搜索 值，则可以通过与'YYYY-MM-DD hh:mm:ss' 值进行比较来获得异常结果。以下示例演示了这一点。它将本地时区更改为UTC，因此内部值（以UTC表示）与显示值（已应用时区校正）之间没有区别。

mysql> CREATE TABLE t1 (
         a INT,
         ts TIMESTAMP DEFAULT NOW(),
         PRIMARY KEY (ts)
       );
Query OK, 0 rows affected (0.01 sec)

mysql> -- change to UTC
mysql> SET time_zone = '+00:00';
Query OK, 0 rows affected (0.00 sec)

mysql> -- Simulate NOW() = '2008-12-31 23:59:59'
mysql> SET timestamp = 1230767999;
Query OK, 0 rows affected (0.00 sec)

mysql> INSERT INTO t1 (a) VALUES (1);
Query OK, 1 row affected (0.00 sec)

mysql> -- Simulate NOW() = '2008-12-31 23:59:60'
mysql> SET timestamp = 1230768000;
Query OK, 0 rows affected (0.00 sec)

mysql> INSERT INTO t1 (a) VALUES (2);
Query OK, 1 row affected (0.00 sec)

mysql> -- values differ internally but display the same
mysql> SELECT a, ts, UNIX_TIMESTAMP(ts) FROM t1;
+------+---------------------+--------------------+
| a    | ts                  | UNIX_TIMESTAMP(ts) |
+------+---------------------+--------------------+
|    1 | 2008-12-31 23:59:59 |         1230767999 |
|    2 | 2008-12-31 23:59:59 |         1230768000 |
+------+---------------------+--------------------+
2 rows in set (0.00 sec)

mysql> -- only the non-leap value matches
mysql> SELECT * FROM t1 WHERE ts = '2008-12-31 23:59:59';
+------+---------------------+
| a    | ts                  |
+------+---------------------+
|    1 | 2008-12-31 23:59:59 |
+------+---------------------+
1 row in set (0.00 sec)

mysql> -- the leap value with seconds=60 is invalid
mysql> SELECT * FROM t1 WHERE ts = '2008-12-31 23:59:60';
Empty set, 2 warnings (0.00 sec)

要解决此问题，可以使用基于实际存储在列中的UTC值进行的比较，其中应用了闰秒更正：

mysql> -- selecting using UNIX_TIMESTAMP value return leap value
mysql> SELECT * FROM t1 WHERE UNIX_TIMESTAMP(ts) = 1230768000;
+------+---------------------+
| a    | ts                  |
+------+---------------------+
|    2 | 2008-12-31 23:59:59 |
+------+---------------------+
1 row in set (0.00 sec)

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