[英]COALESCE SUM GROUP?
好的。 我有一個查詢,看起來像這樣:
SELECT
SUM(`order_items`.`quantity`) as `count`,
`menu_items`.`name`
FROM
`orders`,
`menu_items`,
`order_items`
WHERE
`orders`.`id` = `order_items`.`order_id` AND
`menu_items`.`id` = `order_items`.`menu_item_id` AND
`orders`.`date` >= '2008-11-01' AND
`orders`.`date` <= '2008-11-30'
GROUP BY
`menu_items`.`id`
該查詢的目的是顯示在給定日期范圍內售出的商品數量。 雖然這個作品,我現在需要它來顯示一個count
的0
,如果一個特定的項目有日期范圍內沒有銷售。 我嘗試在SUM
周圍使用COALESCE
,但這並沒有解決問題,而且我也沒有真正期望它能做到。 無論如何,有人知道我將如何實現這一目標嗎? 我正在那些時刻中的一刻,我覺得我應該知道這一點,但我想不起來。
干杯
如果將日期條件放在JOIN
子句中,則無需任何子查詢即可完成此操作。
以下是我在MySQL 5.0上測試過的代碼。
SELECT m.name, COALESCE(SUM(oi.quantity), 0) AS count
FROM menu_items AS m
LEFT OUTER JOIN (
order_items AS oi JOIN orders AS o
ON (o.id = oi.order_id)
) ON (m.id = oi.menu_item_id
AND o.`date` BETWEEN '2008-11-01' AND '2008-11-30')
GROUP BY m.id;
輸出:
+--------+-------+
| name | count |
+--------+-------+
| bread | 2 |
| milk | 1 |
| honey | 2 |
| cheese | 0 |
+--------+-------+
這是MySQL風格的DDL和設置代碼:
DROP TABLE IF EXISTS menu_items;
CREATE TABLE menu_items (
id INT PRIMARY KEY,
name VARCHAR(10)
) TYPE=InnoDB;
DROP TABLE IF EXISTS orders;
CREATE TABLE orders (
id INT PRIMARY KEY,
`date` DATE
) TYPE=InnoDB;
DROP TABLE IF EXISTS order_items;
CREATE TABLE order_items (
order_id INT,
menu_item_id INT,
quantity INT,
PRIMARY KEY (order_id, menu_item_id),
FOREIGN KEY (order_id) REFERENCES orders(id),
FOREIGN KEY (menu_item_id) REFERENCES menu_items(id)
) TYPE=InnoDB;
INSERT INTO menu_items VALUES
(1, 'bread'),
(2, 'milk'),
(3, 'honey'),
(4, 'cheese');
INSERT INTO orders VALUES
(1, '2008-11-02'),
(2, '2008-11-03'),
(3, '2008-10-29');
INSERT INTO order_items VALUES
(1, 1, 1),
(1, 3, 1),
(2, 1, 1),
(2, 2, 1),
(2, 3, 1),
(3, 4, 10);
Randy的答案很接近,但是where語句刪除了該日期范圍內不屬於任何訂單的那些物品的任何提及。
請注意,“左聯接”與您按照已完成的方式(即內部聯接)在where子句中鏈接表不同。 我建議您閱讀不同類型的SQL連接(內部,外部,交叉)。
本質上,您需要將從Randy的查詢中獲得的數據與項目的源列表相結合。 使用子選擇將執行以下操作:
SELECT
name
, nvl(count, 0) as count
FROM
menu_items items
LEFT JOIN (
SELECT
menu_items.id
, SUM(order_items.quantity) as count
FROM
menu_items
LEFT JOIN order_items ON menu_items.id = order_items.menu_item_id
LEFT JOIN orders ON orders.id = order_items.order_id
WHERE
"date" between to_date('2008-11-01','YYYY-MM-DD') and to_date('2008-11-30','YYYY-MM-DD')
GROUP BY
menu_items.id
) counts on items.id = counts.id;
這在Oracle 10g BTW中。 我懷疑您使用的是Oracle,因此您需要轉換為自己的數據庫。
運行測試將顯示以下內容:
SQL> create table menu_items ( id number, name varchar2(10));
create table order_items (order_id number, menu_item_id number, quantity number);
create table orders (id number, "date" date);
Table created.
SQL>
Table created.
SQL>
Table created.
SQL>
insert into menu_items values (1, 'bread');
insert into menu_items values (2, 'milk');
insert into menu_items values (3, 'honey');
insert into menu_items values (4, 'cheese');
SQL>
1 row created.
SQL>
1 row created.
SQL>
1 row created.
SQL>
1 row created.
SQL>
insert into orders values (1, to_date('2008-11-02', 'YYYY-MM-DD'));
insert into orders values (2, to_date('2008-11-03', 'YYYY-MM-DD'));
insert into orders values (3, to_date('2008-10-29', 'YYYY-MM-DD'));SQL>
1 row created.
SQL>
1 row created.
SQL>
insert into order_items values (1, 1, 1);
insert into order_items values (1, 3, 1);
1 row created.
SQL>
1 row created.
SQL>
insert into order_items values (2, 1, 1);
insert into order_items values (2, 2, 1);
insert into order_items values (2, 3, 1);
insert into order_items values (3, 4, 10);
1 row created.
SQL>
1 row created.
SQL>
1 row created.
SQL>
1 row created.
SQL> SQL>
1 row created.
SQL>
SELECT
name
, nvl(count, 0) as count
FROM
menu_items items
LEFT JOIN (
SELECT
menu_items.id
, SUM(order_items.quantity) as count
FROM
menu_items
LEFT JOIN order_items ON menu_items.id = order_items.menu_item_id
LEFT JOIN orders ON orders.id = order_items.order_id
WHERE
"date" between to_date('2008-11-01','YYYY-MM-DD') and to_date('2008-11-30','YYYY-MM-DD')
GROUP BY
menu_iteSQL> 2 3 4 5 6 7 ms.id
) counts on items.id = counts.id; 8 9 10 11 12 13 14 15 16 17 18
NAME COUNT
---------- ----------
bread 2
milk 1
honey 2
cheese 0
SQL>
drop table menu_items;
drop table order_items;
drop table orders;SQL>
Table dropped.
SQL>
Table dropped.
SQL>
Table dropped.
SQL>
PS:不好的做法是使用“日期”作為列名,因為它(在大多數情況下)是類型名,並可能導致查詢和解析問題。
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