Question

我正在尝试生成一个表，其中列出了所有区号，办公室代码组合以及具有该区号，办公室代码组合的订户数量。

CREATE TABLE lines 
(
    portid integer NOT NULL primary key,
    areacode varchar(3), --subscriber area code
    officecode varchar(3), --subscriber office code
    stationcode varchar(4), --subscriber station code
    state varchar(4) NOT NULL, --line state BUSY, IDLE

    foreign key (portid) references facilities(portid) on delete cascade
);

CREATE TABLE subscribers 
(
    portid integer NOT NULL,
    name varchar(30) NOT NULL,
    address varchar(50),
    primary key (portid, name),
    foreign key (portid)  references facilities(portid) on delete cascade
);

SELECT 
    AREACODE, OFFICECODE, COUNT(SUBSCRIBERS.PORTID = LINES.PORTID)
FROM 
    LINES
INNER JOIN 
    SUBSCRIBERS ON SUBSCRIBERS.PORTID = LINES.PORTID;

但这仅输出819 | 227 | 50。它输出的是订户总数，而不是每个区号和局号组合的订户数。我在做什么错了？

Answer 1

您将希望使用以下内容：

SELECT LINES.AREACODE, LINES.OFFICECODE, COUNT(*) AS SUBS
FROM LINES INNER JOIN SUBSCRIBERS ON SUBSCRIBERS.PORTID=LINES.PORTID
GROUP BY LINES.AREACODE, LINES.OFFICECODE

没有GROUP BY子句，查询将为联接的数据集中的每个记录输出一行。

要输出计数符合某些条件的记录，您可以添加一个HAVING子句，例如：

SELECT LINES.AREACODE, LINES.OFFICECODE, COUNT(*) AS SUBS
FROM LINES INNER JOIN SUBSCRIBERS ON SUBSCRIBERS.PORTID=LINES.PORTID
GROUP BY LINES.AREACODE, LINES.OFFICECODE
HAVING COUNT(*) = 3

Answer 2

一个分组或嵌套选择可以使您找到想要的东西，我想出了

SELECT areacode, officecode, lines.portid, count(*) from lines inner join 
subscribers on subscribers.portid=lines.portid group by areacode, officecode;

如何获得单独表格中每一行的计数？

2 个答案: