将 SELECT COUNT(*) 查询结果分配给 Java 变量
我在将 SELECT COUNT(*) 查询的结果分配给 Java 变量时遇到问题。我将查询结果分配给 ResultSet。然后，我尝试检索计数的值并将其分配给变量。我在尝试执行此操作时遇到错误。
这是我的代码：
ResultSet rc1 = null;
int rowCount1;
Statement stat = conn.createStatement();
rc1 = stat.executeQuery("SELECT COUNT(*) AS rowcount1
FROM Signal WHERE SignalId = 1;");
if (rc1.next())
rowCount1 = rc1.getInt("rowcount1");
然后我收到以下错误：
java.sql.SQLException：没有这样的列：'rowcount1'
在 org.sqlite.RS.findColumn(RS.java:116)
在 org.sqlite.RS.getInt(RS.java:219)
显然，问题在于尝试将 AS 之后的内容分配给变量时。我找不到很多关于包含 AS 的查询的信息。我在未计数的查询中遇到了同样的错误。例如，如果我有以下代码：
ResultSet rp1 = null;
int rowCount1 = 0;
Statement stat = conn.createStatement();
rp1 = stat.executeQuery("SELECT Signal AS Sig1
FROM Observations WHERE SignalId = 1;");
if (rp1.next())
rowCount1 = rp1.getInt("rowcount1");
我会得到与之前的代码相同的错误（没有这样的列：rowCount1）。我做错了什么？我确保我正在读取的表包含正确的值，因此查询必须为真。
I have been having problems assigning the result of a SELECT COUNT(*) query to a Java variable. I am assigning the result of the query to a ResultSet. Then, I am trying to retrieve the value of the count and assigning it to a variable. I am getting an error when trying to do this.
Here is my code:
ResultSet rc1 = null;
int rowCount1;
Statement stat = conn.createStatement();
rc1 = stat.executeQuery("SELECT COUNT(*) AS rowcount1
FROM Signal WHERE SignalId = 1;");
if (rc1.next())
rowCount1 = rc1.getInt("rowcount1");
Then I get the following error:
java.sql.SQLException: no such column: 'rowcount1'
at org.sqlite.RS.findColumn(RS.java:116)
at org.sqlite.RS.getInt(RS.java:219)
Apparently, the problem is when trying to assign what goes after AS to a variable. I can't find a lot of information on queries containing AS. I get the same error with queries where I am not counting. For example if I have the following code:
ResultSet rp1 = null;
int rowCount1 = 0;
Statement stat = conn.createStatement();
rp1 = stat.executeQuery("SELECT Signal AS Sig1
FROM Observations WHERE SignalId = 1;");
if (rp1.next())
rowCount1 = rp1.getInt("rowcount1");
I get the same error with the previous code (no such column: rowCount1). What I am doing wrong? I am making sure the table I am reading contains the correct values so the query has to be true.
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评论（2）
只需使用 rp1.getInt(1) 即可——这会以 int 形式返回结果集中的第一列——这就是您想要的。
如果您有更多值，请使用 rp1.getInt(2) 来获取第二个值等...
Simply use
rp1.getInt(1)-- this returns the first column from the resultset as an int -- which is what you want.If you have more values use
rp1.getInt(2)to get the second value etc...第二个示例有一个错误：
将始终失败，因为查询中没有
rowcount1列。The second example has an error:
will always fail because you have no
rowcount1column in your query.