查询 Firebird 3.0 中的变量

Question

此查询无效

select a.id from users a where a.LOGIN = 'Test' into :useriden
WITH T AS (
SELECT
   ID,
   FIO,
   PWDHASH,
   ATTIME,
   ROW_NUMBER() OVER(ORDER BY ATTIME DESC) AS RN
FROM USERSPWDHASHHISTORY
WHERE USERID = :useriden)
SELECT
   ID, 
   FIO,
   PWDHASH,
   ATTIME
FROM T
WHERE RN > 3

如何正确初始化数据库查询中的变量？不在存储过程或触发器中。

Answer 1

你想要的在 DSQL 中无法完成，在 PSQL 中这至少是一个语法错误，因为你没有终止语句。

但是，您不需要为此单独声明，您可以内联查询

WITH T AS (
    SELECT
       ID,
       FIO,
       PWDHASH,
       ATTIME,
       ROW_NUMBER() OVER(ORDER BY h.ATTIME DESC) AS RN
    FROM USERSPWDHASHHISTORY
    WHERE USERID = (select a.id from users a where a.LOGIN = 'Test'))
SELECT
   ID, 
   FIO,
   PWDHASH,
   ATTIME
FROM T
WHERE RN > 3

或使用联接而不是 sub-query

WITH T AS (
    SELECT
       h.ID,
       h.FIO,
       h.PWDHASH,
       h.ATTIME,
       ROW_NUMBER() OVER(ORDER BY ATTIME DESC) AS RN
    FROM USERSPWDHASHHISTORY h
    inner join users u on h.userid = u.id
    WHERE u.LOGIN = 'Test')
SELECT
   ID, 
   FIO,
   PWDHASH,
   ATTIME
FROM T
WHERE RN > 3

或者，您首先 select id，然后使用 ? id 参数占位符准备其他查询，使用您 selected 的 id 值准备并执行它以前。

例如，在 Java 中，您可以执行以下操作：

int id = -1;
try (var stmt = connection.createStatement();
     var rs = rs.executeQuery("select a.id from users a where a.LOGIN = 'Test'")) {
    if (rs.next()) {
        id = rs.getInt(1);
    }
}
try (var stmt = connection.prepareStatement("""
        WITH T AS (
        SELECT
           ID,
           FIO,
           PWDHASH,
           ATTIME,
           ROW_NUMBER() OVER(ORDER BY ATTIME DESC) AS RN
        FROM USERSPWDHASHHISTORY
        WHERE USERID = ?)
        SELECT
           ID, 
           FIO,
           PWDHASH,
           ATTIME
        FROM T
        WHERE RN > 3
        """)) {

    stmt.setInt(1, id);
    try (var rs = stmt.executeQuery()) {
        // process result set
    }
}

但是，鉴于此特定示例可以在一个语句中完成，考虑到执行两个语句和相关网络往返的不必要开销，这种解决方案不是首选。

查询 Firebird 3.0 中的变量

Variables in queries Firebird 3.0

sql

variables

firebird

firebird-3.0