mysql - 如何为 MySQL 变量设置时间戳？

Question

无法弄清楚为什么 @previousEndTime 变量只有 YEAR 值。

我的 test_table 上的示例数据:

| id |   name |                     start |                       end |
|----|--------|---------------------------|---------------------------|
|  2 | test 1 | January, 01 2016 12:00:00 | January, 01 2016 13:00:00 |
|  3 | test 1 | January, 02 2016 11:00:00 | January, 02 2016 12:00:00 |
|  5 | test 1 | January, 03 2016 15:00:00 | January, 03 2016 16:00:00 |
|  6 | test 2 | January, 01 2016 10:00:00 | January, 01 2016 11:00:00 |
|  7 | test 2 | January, 02 2016 17:00:00 | January, 02 2016 18:00:00 |



SELECT
        id,
        name,
        @previousEndTime,
        @previousEndTime := end     
    FROM
        test_table, (SELECT @previousEndTime := 0) var
    ORDER BY name, id;

当前结果:

| id |   name | @previousEndTime | @previousEndTime := end |
|----|--------|------------------|-------------------------|
|  2 | test 1 |                0 |     2016-01-01 13:00:00 |
|  3 | test 1 |             2016 |     2016-01-02 12:00:00 |
|  5 | test 1 |             2016 |     2016-01-03 16:00:00 |
|  6 | test 2 |             2016 |     2016-01-01 11:00:00 |
|  7 | test 2 |             2016 |     2016-01-02 18:00:00 |

预期结果:

| id |   name |     @previousEndTime| @previousEndTime := end |
|----|--------|---------------------|-------------------------|
|  2 | test 1 |                0    |     2016-01-01 13:00:00 |
|  3 | test 1 |2016-01-01 13:00:00  |     2016-01-02 12:00:00 |
|  5 | test 1 |2016-01-02 12:00:00  |     2016-01-03 16:00:00 |
|  6 | test 2 |2016-01-03 16:00:00  |     2016-01-01 11:00:00 |
|  7 | test 2 |2016-01-01 11:00:00  |     2016-01-02 18:00:00 |

请检查这个FIDDLE

注意:

我尝试过的其他方法:

@previousEndTime := CONCAT('',end,'')

@previousEndTime := TIMESTAMP(CONCAT('',end,''))    

Answer 1

看看这个;)

SQL Fiddle

MySQL 5.6 模式:

DROP TABLE IF EXISTS `test_table`;
CREATE TABLE `test_table` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(50) CHARACTER SET utf8 NOT NULL,
  `start` timestamp NOT NULL DEFAULT '0000-00-00 00:00:00' ON UPDATE CURRENT_TIMESTAMP,
  `end` timestamp NOT NULL DEFAULT '0000-00-00 00:00:00' ON UPDATE CURRENT_TIMESTAMP,
  PRIMARY KEY (`id`)
);
INSERT INTO `test_table` VALUES ('2', 'test 1', '2016-01-01 12:00:00', '2016-01-01 13:00:00');
INSERT INTO `test_table` VALUES ('3', 'test 1', '2016-01-02 11:00:00', '2016-01-02 12:00:00');
INSERT INTO `test_table` VALUES ('5', 'test 1', '2016-01-03 15:00:00', '2016-01-03 16:00:00');
INSERT INTO `test_table` VALUES ('6', 'test 2', '2016-01-01 10:00:00', '2016-01-01 11:00:00');
INSERT INTO `test_table` VALUES ('7', 'test 2', '2016-01-02 17:00:00', '2016-01-02 18:00:00');

查询 1:

SELECT
    id,
    name,
    if(@previousEndTime='0000-00-00 00:00:00',0,@previousEndTime),
    @previousEndTime := end     
FROM
    test_table,
    (
        SELECT
            @previousEndTime := '0000-00-00 00:00:00'
    ) var
ORDER BY name, id

Results :

| id |   name | if(@previousEndTime='0000-00-00 00:00:00',0,@previousEndTime) | @previousEndTime := end |
|----|--------|---------------------------------------------------------------|-------------------------|
|  2 | test 1 |                                                             0 |     2016-01-01 13:00:00 |
|  3 | test 1 |                                           2016-01-01 13:00:00 |     2016-01-02 12:00:00 |
|  5 | test 1 |                                           2016-01-02 12:00:00 |     2016-01-03 16:00:00 |
|  6 | test 2 |                                           2016-01-03 16:00:00 |     2016-01-01 11:00:00 |
|  7 | test 2 |                                           2016-01-01 11:00:00 |     2016-01-02 18:00:00 |