如何计算Oracle中两个表的出现次数？

Question

我在Oracle 12c中有两个表，目标是计算table2中所有出现Flag NULL的事件，但是在table1中出现的Names旁边显示0

表1

ID,Name
001,Bob
009,Alice
015,Bob
019,Bob
026,Alice
500,Rob
505,Rob

表2

ID,Flag,Timestamp
001,NULL,02/04/2016 16:33:13,991000
010,NULL,02/04/2016 16:33:14,991000
023,NULL,02/04/2016 16:33:15,991000
019,True,02/04/2016 16:33:16,991000
026,True,02/04/2016 16:33:17,991000
500,NULL,02/04/2016 16:33:18,991000
505,NULL,02/04/2016 16:33:19,991000

我想

Name,COUNT
Alice,0
Bob,1
Rob,2

到目前为止，我的尝试是：

SELECT table1.Name, count(table1.Name) AS count
FROM table2
LEFT OUTER JOIN table1
ON table2.ID = table1.ID
WHERE table2.Flag IS null AND trunc(table2.Timestamp) = TRUNC(SYSDATE)
GROUP BY table1.Name

返回

Name,COUNT
Bob,1
Rob,2

Answer 1

您需要将table1的位置替换为table2并计算table2的id列（以便在不符合连接条件时排除空值）。

SELECT table1.Name, count(table2.id) AS count
FROM table1
LEFT OUTER JOIN table2
ON table2.ID = table1.ID
 AND table2.Flag IS null
GROUP BY table1.Name

Answer 2

请改为尝试：

SELECT table1.Name, count(table2.ID) AS count
FROM table1
LEFT OUTER JOIN table2 ON table2.ID = table1.ID
WHERE table2.Flag IS null
GROUP BY table1.Name