使用LIKE子句计算每个外键的记录数

Question

My image, explanation

• 我需要计算不存在的外键，如图所示，并在列表名称中包含字母“a”。
• 我只能计算值，但无法用字母“a”指定名称。

我正在使用计数：

SELECT l.identifier AS id, l.name AS listName, COUNT(p.list_identifier)
AS regCount FROM list AS l LEFT JOIN person AS p ON l.identifier = p.list_identifier
WHERE p.list_identifier IS NULL GROUP BY l.name;

请帮帮我。

Answer 1

尝试使用left outer join＆amp; COUNT（DISTINCT ...）

SELECT COUNT(DISTINCT l.identifier) AS regCount
FROM list AS l LEFT OUTER JOIN person AS p ON l.identifier = p.list_identifier
WHERE l.Name LIKE '%a%'