如何使 Mysql 变量在查询中起作用
How to make Mysql variables work in a query
我一直在努力尝试在我的 mysql/mariadb 数据库中生成自动聚合代码。我目前正在尝试使用变量的方法。我会提前承认我无论如何都不是数据库专家。我完全是自学成才，并且一直在努力为这个特定问题寻找足够的资源。我在下面包含了简化示例，哦，我正在使用 mariadb 10.1。
这段代码应该可以在 mysql 5.6 和 mariadb 10.0+ 中运行，我已经在 10.1 上测试过它并且可以运行。
这是我的 Table: 并且 SQL FIDDLE <- 由于某种原因不起作用。可能是动态列。我会留下它以防有人知道为什么。
CREATE TABLE data_points
(
id BIGINT NOT NULL AUTO_INCREMENT PRIMARY KEY,
device_id INTEGER,
dtime DATETIME,
sf INTEGER(11), -- sample frequency or interval
agg INTEGER(11), -- aggregation type, actually a fk
data_point BLOB,
PRIMARY KEY (id),
UNIQUE (device_id, dtime, sf, agg)
);
让我们插入一些数据：
INSERT INTO data_points
(device_id, dtime, sf, agg, data_point)
VALUES
(1, '2015-01-02 12:00:00', 1, 60, COLUMN_CREATE('aa', 12, 'ab', 34, 'ac', 45)),
(1, '2015-01-02 13:00:00', 1, 60, COLUMN_CREATE('aa', 12, 'ab', 34, 'ac', 45)),
(1, '2015-01-02 14:00:00', 1, 60, COLUMN_CREATE('aa', 12, 'ab', 34, 'ac', 45)),
(1, '2015-01-02 15:00:00', 1, 60, COLUMN_CREATE('aa', 12, 'ab', 34, 'ac', 45)),
(1, '2015-01-02 16:00:00', 1, 60, COLUMN_CREATE('aa', 12, 'ab', 34, 'ac', 45));
到目前为止，一切正常。我想要做的是在不同的时间段执行聚合，我的最低颗粒期是 60 秒。这是我遇到问题的地方，它可能很明显。
SELECT
@dp_dtime := MAX(dtime),
@dp_aa := MIN(ROUND(COLUMN_GET(data_point, 'aa' AS DOUBLE), 4)),
@dp_ab := MIN(ROUND(COLUMN_GET(data_point, 'ab' AS DOUBLE), 4)),
@dp_ac := MIN(ROUND(COLUMN_GET(data_point, 'ac' AS DOUBLE), 4))
FROM data_points
WHERE
device_id = 1 AND
dtime BETWEEN '2015/01/02 12:00:00' AND '2015/01/17 23:05:00' AND
sf = 60 AND
agg = 1;
INSERT INTO data_points
(device_id, dtime, sf, agg, data_point)
VALUES (8, @dp_dtime, 300, 2, COLUMN_CREATE('aa', @dp_aa, 'ab', @dp_ab, 'ac', @dp_ac));
这最终会创建另一行 NULL 语句中变量所在的所有位置。
select @dp_dtime, @dp_aa, @dp_ab, @pd_ac;
-- This results in NULL, NULL, NULL, NULL
此时我很确定我对变量做错了什么。
很晚了，一天 14 小时。我什至接近？有 better/easier 方法吗？
任何帮助将不胜感激。
编辑：
在我的实际用例中，列数取决于进行聚合的设备类型。列是 excel 样式 'aa' 到 'zz' 可能的。尽管我见过的最大宽度约为 150 列。这听起来像是一个糟糕的设计，但性能却令人惊讶，我分不清这些动态列和实际列之间的区别。 （至少只要你不需要索引它们）
可能是一个简单的错字：我看到了 @_dtime。
在UNIQUE索引中，把dtime放在最后；它将使查询更快。 迷你索引课程： 所有 = 列都应该在复合索引中排在第一位，顺序不限（基数几乎没有区别）。然后你可以放一个'range'（dtime）。范围之后的任何列都不用于过滤。参见 my cookbook。
摆脱id并将UNIQUE索引提升为PRIMARY KEY；它将使查询更快。 迷你索引课程：辅助键（例如您的 UNIQUE）需要在键和数据之间跳转。 PRIMARY KEY 与数据聚类（在 InnoDB 中），从而避免了弹跳。相反，PK 上的 'range scan' 是 table.
上的范围
尝试以下查询。
SQL:
CREATE TABLE data_points
(
id BIGINT NOT NULL AUTO_INCREMENT PRIMARY KEY,
device_id INTEGER,
dtime DATETIME,
sf INTEGER(11), -- sample frequency or interval
agg INTEGER(11), -- aggregation type, actually a fk
data_point BLOB,
UNIQUE (device_id, dtime, sf, agg)
);
INSERT INTO data_points
(device_id, dtime, sf, agg, data_point)
VALUES
(1, '2015-01-02 12:00:00', 1, 1, COLUMN_CREATE('aa', 12, 'ab', 34, 'ac', 45)),
(1, '2015-01-02 13:00:00', 1, 1, COLUMN_CREATE('aa', 12, 'ab', 34, 'ac', 45)),
(1, '2015-01-02 14:00:00', 1, 1, COLUMN_CREATE('aa', 12, 'ab', 34, 'ac', 45)),
(1, '2015-01-02 15:00:00', 1, 1, COLUMN_CREATE('aa', 12, 'ab', 34, 'ac', 45)),
(1, '2015-01-02 16:00:00', 1, 1, COLUMN_CREATE('aa', 12, 'ab', 34, 'ac', 45));
select * from data_points;
SELECT
@dp_dtime := MAX(dtime) as dp_dtime,
@dp_aa := MIN(ROUND(COLUMN_GET(data_point, 'aa' AS DOUBLE), 4)) as dp_aa,
@dp_ab := MIN(ROUND(COLUMN_GET(data_point, 'ab' AS DOUBLE), 4)) as dp_ab,
@dp_ac := MIN(ROUND(COLUMN_GET(data_point, 'ac' AS DOUBLE), 4)) as dp_ac
FROM data_points
WHERE
device_id = 1 AND
dtime BETWEEN '2015/01/02 12:00:00' AND '2015/1/17 23:05:00' AND
sf = 1 AND
agg = 1;
INSERT INTO data_points
(device_id, dtime, sf, agg, data_point)
VALUES (8, @dp_dtime, 300, 2, COLUMN_CREATE('aa', @dp_aa, 'ab', @dp_ab, 'ac', @dp_ac));
select * from data_points;
输出：
mysql> select * from data_points;
+----+-----------+---------------------+------+------+----------------------------+
| id | device_id | dtime | sf | agg | data_point |
+----+-----------+---------------------+------+------+----------------------------+
| 1 | 1 | 2015-01-02 12:00:00 | 1 | 1 | aaabacDZ |
| 2 | 1 | 2015-01-02 13:00:00 | 1 | 1 | aaabacDZ |
| 3 | 1 | 2015-01-02 14:00:00 | 1 | 1 | aaabacDZ |
| 4 | 1 | 2015-01-02 15:00:00 | 1 | 1 | aaabacDZ |
| 5 | 1 | 2015-01-02 16:00:00 | 1 | 1 | aaabacDZ |
+----+-----------+---------------------+------+------+----------------------------+
5 rows in set (0.00 sec)
mysql> SELECT
-> @dp_dtime := MAX(dtime) as dp_dtime,
-> @dp_aa := MIN(ROUND(COLUMN_GET(data_point, 'aa' AS DOUBLE), 4)) as dp_aa,
-> @dp_ab := MIN(ROUND(COLUMN_GET(data_point, 'ab' AS DOUBLE), 4)) as dp_ab,
-> @dp_ac := MIN(ROUND(COLUMN_GET(data_point, 'ac' AS DOUBLE), 4)) as dp_ac
-> FROM data_points
-> WHERE
-> device_id = 1 AND
-> dtime BETWEEN '2015/01/02 12:00:00' AND '2015/1/17 23:05:00' AND
-> sf = 1 AND
-> agg = 1;
+---------------------+---------+---------+---------+
| dp_dtime | dp_aa | dp_ab | dp_ac |
+---------------------+---------+---------+---------+
| 2015-01-02 16:00:00 | 12.0000 | 34.0000 | 45.0000 |
+---------------------+---------+---------+---------+
1 row in set (0.00 sec)
mysql> INSERT INTO data_points
-> (device_id, dtime, sf, agg, data_point)
-> VALUES (8, @dp_dtime, 300, 2, COLUMN_CREATE('aa', @dp_aa, 'ab', @dp_ab, 'ac', @dp_ac));
Query OK, 1 row affected (0.00 sec)
mysql> select * from data_points;
+----+-----------+---------------------+------+------+-------------------------------------------------+
| id | device_id | dtime | sf | agg | data_point |
+----+-----------+---------------------+------+------+-------------------------------------------------+
| 1 | 1 | 2015-01-02 12:00:00 | 1 | 1 | aaabacDZ |
| 2 | 1 | 2015-01-02 13:00:00 | 1 | 1 | aaabacDZ |
| 3 | 1 | 2015-01-02 14:00:00 | 1 | 1 | aaabacDZ |
| 4 | 1 | 2015-01-02 15:00:00 | 1 | 1 | aaabacDZ |
| 5 | 1 | 2015-01-02 16:00:00 | 1 | 1 | aaabacDZ |
| 6 | 8 | 2015-01-02 16:00:00 | 300 | 2 | ▒ aaabac (@ A@ ▒F@ |
+----+-----------+---------------------+------+------+-------------------------------------------------+
6 rows in set (0.00 sec)
我一直在努力尝试在我的 mysql/mariadb 数据库中生成自动聚合代码。我目前正在尝试使用变量的方法。我会提前承认我无论如何都不是数据库专家。我完全是自学成才，并且一直在努力为这个特定问题寻找足够的资源。我在下面包含了简化示例，哦，我正在使用 mariadb 10.1。
这段代码应该可以在 mysql 5.6 和 mariadb 10.0+ 中运行，我已经在 10.1 上测试过它并且可以运行。
这是我的 Table: 并且 SQL FIDDLE <- 由于某种原因不起作用。可能是动态列。我会留下它以防有人知道为什么。
CREATE TABLE data_points
(
id BIGINT NOT NULL AUTO_INCREMENT PRIMARY KEY,
device_id INTEGER,
dtime DATETIME,
sf INTEGER(11), -- sample frequency or interval
agg INTEGER(11), -- aggregation type, actually a fk
data_point BLOB,
PRIMARY KEY (id),
UNIQUE (device_id, dtime, sf, agg)
);
让我们插入一些数据：
INSERT INTO data_points
(device_id, dtime, sf, agg, data_point)
VALUES
(1, '2015-01-02 12:00:00', 1, 60, COLUMN_CREATE('aa', 12, 'ab', 34, 'ac', 45)),
(1, '2015-01-02 13:00:00', 1, 60, COLUMN_CREATE('aa', 12, 'ab', 34, 'ac', 45)),
(1, '2015-01-02 14:00:00', 1, 60, COLUMN_CREATE('aa', 12, 'ab', 34, 'ac', 45)),
(1, '2015-01-02 15:00:00', 1, 60, COLUMN_CREATE('aa', 12, 'ab', 34, 'ac', 45)),
(1, '2015-01-02 16:00:00', 1, 60, COLUMN_CREATE('aa', 12, 'ab', 34, 'ac', 45));
到目前为止，一切正常。我想要做的是在不同的时间段执行聚合，我的最低颗粒期是 60 秒。这是我遇到问题的地方，它可能很明显。
SELECT
@dp_dtime := MAX(dtime),
@dp_aa := MIN(ROUND(COLUMN_GET(data_point, 'aa' AS DOUBLE), 4)),
@dp_ab := MIN(ROUND(COLUMN_GET(data_point, 'ab' AS DOUBLE), 4)),
@dp_ac := MIN(ROUND(COLUMN_GET(data_point, 'ac' AS DOUBLE), 4))
FROM data_points
WHERE
device_id = 1 AND
dtime BETWEEN '2015/01/02 12:00:00' AND '2015/01/17 23:05:00' AND
sf = 60 AND
agg = 1;
INSERT INTO data_points
(device_id, dtime, sf, agg, data_point)
VALUES (8, @dp_dtime, 300, 2, COLUMN_CREATE('aa', @dp_aa, 'ab', @dp_ab, 'ac', @dp_ac));
这最终会创建另一行 NULL 语句中变量所在的所有位置。
select @dp_dtime, @dp_aa, @dp_ab, @pd_ac;
-- This results in NULL, NULL, NULL, NULL
此时我很确定我对变量做错了什么。 很晚了，一天 14 小时。我什至接近？有 better/easier 方法吗？ 任何帮助将不胜感激。
编辑： 在我的实际用例中，列数取决于进行聚合的设备类型。列是 excel 样式 'aa' 到 'zz' 可能的。尽管我见过的最大宽度约为 150 列。这听起来像是一个糟糕的设计，但性能却令人惊讶，我分不清这些动态列和实际列之间的区别。 （至少只要你不需要索引它们）
可能是一个简单的错字：我看到了 @_dtime。
在UNIQUE索引中，把dtime放在最后；它将使查询更快。 迷你索引课程： 所有 = 列都应该在复合索引中排在第一位，顺序不限（基数几乎没有区别）。然后你可以放一个'range'（dtime）。范围之后的任何列都不用于过滤。参见 my cookbook。
摆脱id并将UNIQUE索引提升为PRIMARY KEY；它将使查询更快。 迷你索引课程：辅助键（例如您的 UNIQUE）需要在键和数据之间跳转。 PRIMARY KEY 与数据聚类（在 InnoDB 中），从而避免了弹跳。相反，PK 上的 'range scan' 是 table.
尝试以下查询。
SQL:
CREATE TABLE data_points
(
id BIGINT NOT NULL AUTO_INCREMENT PRIMARY KEY,
device_id INTEGER,
dtime DATETIME,
sf INTEGER(11), -- sample frequency or interval
agg INTEGER(11), -- aggregation type, actually a fk
data_point BLOB,
UNIQUE (device_id, dtime, sf, agg)
);
INSERT INTO data_points
(device_id, dtime, sf, agg, data_point)
VALUES
(1, '2015-01-02 12:00:00', 1, 1, COLUMN_CREATE('aa', 12, 'ab', 34, 'ac', 45)),
(1, '2015-01-02 13:00:00', 1, 1, COLUMN_CREATE('aa', 12, 'ab', 34, 'ac', 45)),
(1, '2015-01-02 14:00:00', 1, 1, COLUMN_CREATE('aa', 12, 'ab', 34, 'ac', 45)),
(1, '2015-01-02 15:00:00', 1, 1, COLUMN_CREATE('aa', 12, 'ab', 34, 'ac', 45)),
(1, '2015-01-02 16:00:00', 1, 1, COLUMN_CREATE('aa', 12, 'ab', 34, 'ac', 45));
select * from data_points;
SELECT
@dp_dtime := MAX(dtime) as dp_dtime,
@dp_aa := MIN(ROUND(COLUMN_GET(data_point, 'aa' AS DOUBLE), 4)) as dp_aa,
@dp_ab := MIN(ROUND(COLUMN_GET(data_point, 'ab' AS DOUBLE), 4)) as dp_ab,
@dp_ac := MIN(ROUND(COLUMN_GET(data_point, 'ac' AS DOUBLE), 4)) as dp_ac
FROM data_points
WHERE
device_id = 1 AND
dtime BETWEEN '2015/01/02 12:00:00' AND '2015/1/17 23:05:00' AND
sf = 1 AND
agg = 1;
INSERT INTO data_points
(device_id, dtime, sf, agg, data_point)
VALUES (8, @dp_dtime, 300, 2, COLUMN_CREATE('aa', @dp_aa, 'ab', @dp_ab, 'ac', @dp_ac));
select * from data_points;
输出：
mysql> select * from data_points;
+----+-----------+---------------------+------+------+----------------------------+
| id | device_id | dtime | sf | agg | data_point |
+----+-----------+---------------------+------+------+----------------------------+
| 1 | 1 | 2015-01-02 12:00:00 | 1 | 1 | aaabacDZ |
| 2 | 1 | 2015-01-02 13:00:00 | 1 | 1 | aaabacDZ |
| 3 | 1 | 2015-01-02 14:00:00 | 1 | 1 | aaabacDZ |
| 4 | 1 | 2015-01-02 15:00:00 | 1 | 1 | aaabacDZ |
| 5 | 1 | 2015-01-02 16:00:00 | 1 | 1 | aaabacDZ |
+----+-----------+---------------------+------+------+----------------------------+
5 rows in set (0.00 sec)
mysql> SELECT
-> @dp_dtime := MAX(dtime) as dp_dtime,
-> @dp_aa := MIN(ROUND(COLUMN_GET(data_point, 'aa' AS DOUBLE), 4)) as dp_aa,
-> @dp_ab := MIN(ROUND(COLUMN_GET(data_point, 'ab' AS DOUBLE), 4)) as dp_ab,
-> @dp_ac := MIN(ROUND(COLUMN_GET(data_point, 'ac' AS DOUBLE), 4)) as dp_ac
-> FROM data_points
-> WHERE
-> device_id = 1 AND
-> dtime BETWEEN '2015/01/02 12:00:00' AND '2015/1/17 23:05:00' AND
-> sf = 1 AND
-> agg = 1;
+---------------------+---------+---------+---------+
| dp_dtime | dp_aa | dp_ab | dp_ac |
+---------------------+---------+---------+---------+
| 2015-01-02 16:00:00 | 12.0000 | 34.0000 | 45.0000 |
+---------------------+---------+---------+---------+
1 row in set (0.00 sec)
mysql> INSERT INTO data_points
-> (device_id, dtime, sf, agg, data_point)
-> VALUES (8, @dp_dtime, 300, 2, COLUMN_CREATE('aa', @dp_aa, 'ab', @dp_ab, 'ac', @dp_ac));
Query OK, 1 row affected (0.00 sec)
mysql> select * from data_points;
+----+-----------+---------------------+------+------+-------------------------------------------------+
| id | device_id | dtime | sf | agg | data_point |
+----+-----------+---------------------+------+------+-------------------------------------------------+
| 1 | 1 | 2015-01-02 12:00:00 | 1 | 1 | aaabacDZ |
| 2 | 1 | 2015-01-02 13:00:00 | 1 | 1 | aaabacDZ |
| 3 | 1 | 2015-01-02 14:00:00 | 1 | 1 | aaabacDZ |
| 4 | 1 | 2015-01-02 15:00:00 | 1 | 1 | aaabacDZ |
| 5 | 1 | 2015-01-02 16:00:00 | 1 | 1 | aaabacDZ |
| 6 | 8 | 2015-01-02 16:00:00 | 300 | 2 | ▒ aaabac (@ A@ ▒F@ |
+----+-----------+---------------------+------+------+-------------------------------------------------+
6 rows in set (0.00 sec)