SQL语句中,表示计算个数的函数是___? A.Count() B.Sum() C.Distinct() D.Max()
时间: 2023-02-09 13:56:05 浏览: 116
A. Count() 是用来计算个数的函数。例如,你可以使用如下的 SQL 语句来计算表中的行数:
```
SELECT COUNT(*) FROM table_name;
```
B. Sum() 是用来计算总和的函数。例如,你可以使用如下的 SQL 语句来计算表中某一列的总和:
```
SELECT SUM(column_name) FROM table_name;
```
C. Distinct() 用来去重,它会返回唯一不同的值。例如,你可以使用如下的 SQL 语句来统计表中某一列不同的值的个数:
```
SELECT COUNT(DISTINCT column_name) FROM table_name;
```
D. Max() 是用来求最大值的函数。例如,你可以使用如下的 SQL 语句来求表中某一列的最大值:
```
SELECT MAX(column_name) FROM table_name;
```
相关问题
SELECT a.supplier_id, count(DISTINCT a.order_id) AS totalcount, sum(IFNULL(b.receipt_amount, 0)) / 100 as total_amount, sum(IFNULL(b.sell_commission, 0)) / 100 as total_sellcommAmount, count(DISTINCT IF(b.channel_code = 61, a.order_id, NULL)) AS channelcode61_count, sum( IF(b.channel_code = 61, IFNULL(b.receipt_amount, 0), 0) ) / 100 as channelcode61_amount, sum( IF(b.channel_code = 61, IFNULL(b.sell_commission, 0), 0) ) / 100 as channelcode61_sellcommAmount FROM settle_order a INNER JOIN settle_order_receipt b ON a.order_id = b.order_id WHERE a.is_del = 0 AND a.order_type IN (70, 75) AND a.order_time >= '2023-05-28 00:00:00' AND a.order_time < '2023-05-29 00:00:00' AND a.supplier_id in ( 78, 63, 58, 57, 64, 72, 71, 74, 83, 77, 70, 69, 67, 82, 65, 87, 73, 59, 66, 60, 86, 85, 79, 80, 84, 90 ) GROUP BY a.supplier_id order by a.supplier_id asc
感谢提供SQL语句。根据该SQL语句,可能可以通过以下几个方面进行优化:
1. 调整JOIN关系
可以尝试调整JOIN关系,优先选择小表作为驱动表(即在ON子句中使用小表的主键进行连接)。此外,如果可能,也可以考虑使用子查询或LEFT JOIN代替INNER JOIN。
2. 减少子查询
可以尝试使用JOIN或LEFT JOIN来代替子查询,以避免多次查询数据库。
3. 避免使用函数
在SELECT语句中使用函数会增加查询的开销,因此应尽量避免使用函数。如果可以,可以考虑在代码中使用变量进行计算。
4. 使用索引
可以根据查询条件设置索引,以加快查询速度。例如,在该SQL中可以设置a.is_del、a.order_type、a.order_time和a.supplier_id的索引。
综上,以下是一个可能的优化SQL示例:
```
SELECT
a.supplier_id,
COUNT(DISTINCT a.order_id) AS totalcount,
SUM(IFNULL(b.receipt_amount, 0)) / 100 AS total_amount,
SUM(IFNULL(b.sell_commission, 0)) / 100 AS total_sellcommAmount,
COUNT(DISTINCT IF(b.channel_code = 61, a.order_id, NULL)) AS channelcode61_count,
SUM(IF(b.channel_code = 61, IFNULL(b.receipt_amount, 0), 0)) / 100 AS channelcode61_amount,
SUM(IF(b.channel_code = 61, IFNULL(b.sell_commission, 0), 0)) / 100 AS channelcode61_sellcommAmount
FROM
(SELECT * FROM settle_order WHERE is_del = 0 AND order_type IN (70, 75) AND order_time >= '2023-05-28 00:00:00' AND order_time < '2023-05-29 00:00:00' AND supplier_id IN (78, 63, 58, 57, 64, 72, 71, 74, 83, 77, 70, 69, 67, 82, 65, 87, 73, 59, 66, 60, 86, 85, 79, 80, 84, 90)) a
LEFT JOIN (SELECT * FROM settle_order_receipt) b ON a.order_id = b.order_id
GROUP BY
a.supplier_id
ORDER BY
a.supplier_id ASC
```
需要注意的是,优化SQL语句需要结合具体的数据库环境和数据情况进行,以上只是一个可能的示例,具体优化效果需要测试验证。
SELECT t1.supplier_id,IFNULL(t1.receiptcount,0) as receipt_count,IFNULL(t1.receiptamount,0) as receipt_amount,IFNULL(t2.refundcount,0) as refund_count,IFNULL(t2.refundamount,0) as refund_amount from ( SELECT a.supplier_id, count(DISTINCT a.order_id) AS receiptcount, sum(IFNULL(b.receipt_amount,0))/100 AS receiptamount FROM order_info a left JOIN order_receipt b ON a.order_id = b.order_id WHERE a.order_type IN (70, 75) AND a.is_del = 0 AND a.order_state IN (40, 50, 60) AND a.create_time >= '2023-05-28 00:00:00' AND a.create_time < '2023-05-29 00:00:00' AND a.supplier_id in ( 78,63,58,57,64,72,71,74,83,77,70,69,67,82,65,87,73,59,66,60,86,85,79,80,84,90 ) GROUP BY a.supplier_id order by a.supplier_id ASC ) t1 LEFT JOIN ( select c.supplier_id,count(DISTINCT c.order_id) as refundcount,sum(IFNULL(c.refund_amount,0)) / 100 as refundamount from order_refund c LEFT JOIN order_info d on c.order_id = d.order_id WHERE d.order_type in (70,75) AND d.order_state IN (40, 50, 60) and c.refund_state =13 AND c.is_del = 0 and c.create_time >= '2023-05-28 00:00:00' AND c.create_time < '2023-05-29 00:00:00' AND c.supplier_id in ( 78,63,58,57,64,72,71,74,83,77,70,69,67,82,65,87,73,59,66,60,86,85,79,80,84,90 ) GROUP BY c.supplier_id ) t2 on t1.supplier_id = t2.supplier_id order by t1.supplier_id asc
这是一个比较复杂的 SQL 语句,但是根据您提供的信息,我们可以从以下几个方面来考虑进行优化:
1.使用 EXISTS 子查询替代 LEFT JOIN
在语句中,我们使用了两个 LEFT JOIN 子查询,这在数据量大的情况下可能会影响查询性能。我们可以考虑使用 EXISTS 子查询替代 LEFT JOIN,如下所示:
```
SELECT t1.supplier_id,
IFNULL(t1.receiptcount, 0) AS receipt_count,
IFNULL(t1.receiptamount, 0) AS receipt_amount,
IFNULL(t2.refundcount, 0) AS refund_count,
IFNULL(t2.refundamount, 0) AS refund_amount
FROM (SELECT a.supplier_id,
count(DISTINCT a.order_id) AS receiptcount,
sum(IFNULL(b.receipt_amount, 0)) / 100 AS receiptamount
FROM order_info a
WHERE a.order_type IN (70, 75)
AND a.is_del = 0
AND a.order_state IN (40, 50, 60)
AND a.create_time >= '2023-05-28 00:00:00'
AND a.create_time < '2023-05-29 00:00:00'
AND a.supplier_id IN (78, 63, 58, 57, 64, 72, 71, 74, 83, 77, 70, 69, 67, 82, 65, 87, 73, 59, 66, 60, 86, 85, 79, 80, 84, 90)
AND EXISTS (SELECT 1 FROM order_receipt b WHERE a.order_id = b.order_id)
GROUP BY a.supplier_id
ORDER BY a.supplier_id ASC) t1
LEFT JOIN (SELECT c.supplier_id,
count(DISTINCT c.order_id) AS refundcount,
sum(IFNULL(c.refund_amount, 0)) / 100 AS refundamount
FROM order_refund c
WHERE c.refund_state = 13
AND c.is_del = 0
AND c.create_time >= '2023-05-28 00:00:00'
AND c.create_time < '2023-05-29 00:00:00'
AND c.supplier_id IN (78, 63, 58, 57, 64, 72, 71, 74, 83, 77, 70, 69, 67, 82, 65, 87, 73, 59, 66, 60, 86, 85, 79, 80, 84, 90)
AND EXISTS (SELECT 1 FROM order_info d WHERE c.order_id = d.order_id AND d.order_type IN (70, 75) AND d.order_state IN (40, 50, 60)))
GROUP BY c.supplier_id) t2 ON t1.supplier_id = t2.supplier_id
ORDER BY t1.supplier_id ASC;
```
2.尽可能减少使用 IFNULL 函数
在语句中,我们使用了 IFNULL 函数来处理 NULL 值,这可能会影响查询性能。我们可以尽可能减少使用 IFNULL 函数,改用 COALESCE 函数,如下所示:
```
SELECT t1.supplier_id,
COALESCE(t1.receiptcount, 0) AS receipt_count,
COALESCE(t1.receiptamount, 0) AS receipt_amount,
COALESCE(t2.refundcount, 0) AS refund_count,
COALESCE(t2.refundamount, 0) AS refund_amount
FROM (SELECT a.supplier_id,
count(DISTINCT a.order_id) AS receiptcount,
sum(COALESCE(b.receipt_amount, 0)) / 100 AS receiptamount
FROM order_info a
WHERE a.order_type IN (70, 75)
AND a.is_del = 0
AND a.order_state IN (40, 50, 60)
AND a.create_time >= '2023-05-28 00:00:00'
AND a.create_time < '2023-05-29 00:00:00'
AND a.supplier_id IN (78, 63, 58, 57, 64, 72, 71, 74, 83, 77, 70, 69, 67, 82, 65, 87, 73, 59, 66, 60, 86, 85, 79, 80, 84, 90)
AND EXISTS (SELECT 1 FROM order_receipt b WHERE a.order_id = b.order_id)
GROUP BY a.supplier_id
ORDER BY a.supplier_id ASC) t1
LEFT JOIN (SELECT c.supplier_id,
count(DISTINCT c.order_id) AS refundcount,
sum(COALESCE(c.refund_amount, 0)) / 100 AS refundamount
FROM order_refund c
WHERE c.refund_state = 13
AND c.is_del = 0
AND c.create_time >= '2023-05-28 00:00:00'
AND c.create_time < '2023-05-29 00:00:00'
AND c.supplier_id IN (78, 63, 58, 57, 64, 72, 71, 74, 83, 77, 70, 69, 67, 82, 65, 87, 73, 59, 66, 60, 86, 85, 79, 80, 84, 90)
AND EXISTS (SELECT 1 FROM order_info d WHERE c.order_id = d.order_id AND d.order_type IN (70, 75) AND d.order_state IN (40, 50, 60)))
GROUP BY c.supplier_id) t2 ON t1.supplier_id = t2.supplier_id
ORDER BY t1.supplier_id ASC;
```
3.尽可能减少使用 DISTINCT 关键字
在语句中,我们使用了 DISTINCT 关键字来去重,这可能会影响查询性能。我们可以尽可能减少使用 DISTINCT 关键字,改用 GROUP BY 子句,如下所示:
```
SELECT t1.supplier_id,
COALESCE(t1.receiptcount, 0) AS receipt_count,
COALESCE(t1.receiptamount, 0) AS receipt_amount,
COALESCE(t2.refundcount, 0) AS refund_count,
COALESCE(t2.refundamount, 0) AS refund_amount
FROM (SELECT a.supplier_id,
COUNT(a.order_id) AS receiptcount,
SUM(COALESCE(b.receipt_amount, 0)) / 100 AS receiptamount
FROM order_info a
LEFT JOIN order_receipt b ON a.order_id = b.order_id
WHERE a.order_type IN (70, 75)
AND a.is_del = 0
AND a.order_state IN (40, 50, 60)
AND a.create_time >= '2023-05-28 00:00:00'
AND a.create_time < '2023-05-29 00:00:00'
AND a.supplier_id IN (78, 63, 58, 57, 64, 72, 71, 74, 83, 77, 70, 69, 67, 82, 65, 87, 73, 59, 66, 60, 86, 85, 79, 80, 84, 90)
GROUP BY a.supplier_id
ORDER BY a.supplier_id ASC) t1
LEFT JOIN (SELECT c.supplier_id,
COUNT(c.order_id) AS refundcount,
SUM(COALESCE(c.refund_amount, 0)) / 100 AS refundamount
FROM order_refund c
LEFT JOIN order_info d ON c.order_id = d.order_id
WHERE c.refund_state = 13
AND c.is_del = 0
AND c.create_time >= '2023-05-28 00:00:00'
AND c.create_time < '2023-05-29 00:00:00'
AND c.supplier_id IN (78, 63, 58, 57, 64, 72, 71, 74, 83, 77, 70, 69, 67, 82, 65, 87, 73, 59, 66, 60, 86, 85, 79, 80, 84, 90)
AND d.order_type IN (70, 75)
AND d.order_state IN (40, 50, 60)
GROUP BY c.supplier_id) t2 ON t1.supplier_id = t2.supplier_id
ORDER BY t1.supplier_id ASC;
```
以上是三个简单的优化建议,具体优化方案需要根据实际情况进行调整。
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