如何比较sql中相同条件的两个实例？

我有以下表格：

CREATE TABLE researcher 
(
    rid PRIMARY KEY,
    name,
    institution,
    city,
    country
)

CREATE TABLE paper 
(
    title PRIMARY KEY,
    journal,
    volume,
    number,
    year
)

CREATE TABLE author 
(
    resid FOREIGN KEY REFERENCES researcher.rid,
    title FOREIGN KEY REFERENCES paper.title
)

我需要在SQL查询中列出2019年发表论文比2018年更多的期刊

我试过这个：

SELECT
    journal
FROM
    paper
GROUP BY
    journal
HAVING
    COUNT(title)
WHERE
    year = 2019 > year = 2018

---

既然我不能有

条件>条件

，我该如何解决这个问题

使用条件表达式

SELECT journal
FROM PAPER
GROUP BY journal
HAVING SUM(CASE WHEN year = 2019 THEN 1 ELSE 0 END) > SUM(CASE WHEN year = 2018 THEN 1 ELSE 0 END);

---

请记住，在SQL中，

SELECT

语句的逻辑顺序实际上是：

从

在哪里

分组

拥有

挑选

订购人

考虑到这一点

步骤1：获取期刊列表以及他们在每个特定年份的论文数量： 步骤2：在外部查询中筛选它： （@GordonLinoff的答案是通过将谓词移动到

HAVING

子句，而我更喜欢使用外部查询，从而在单个查询中实现这一点）

SELECT
    journal,
    [year]
    COUNT( CASE WHEN [year] = 2018 THEN 1 END ) AS PaperCountIn2018,
    COUNT( CASE WHEN [year] = 2019 THEN 1 END ) AS PaperCountIn2019
FROM
    paper
GROUP BY
    journal,
    [year]

SELECT
    journalPaperCounts.*
FROM
    (
        SELECT
            journal,
            [year]
            COUNT( CASE WHEN [year] = 2018 THEN 1 END ) AS PaperCountIn2018,
            COUNT( CASE WHEN [year] = 2019 THEN 1 END ) AS PaperCountIn2019
        FROM
            paper
        GROUP BY
            journal,
            [year]
    ) AS journalPaperCounts
WHERE
    journalPaperCounts.PaperCountIn2018 > PaperCountIn2019