[英]Selecting same column values from two tables
我正在struts上做一个项目,在其中我想比较两个表的行值,并希望获得匹配的列作为结果集,而我想从结果集中不取出匹配的列。 我正在执行以下编码,但我总是将3作为columnNumber。 请帮助我获得确切的结果。
public class ResultDAO {
public int correctAnswer() throws Exception {
int columnsNumber=0;
Connection con=null;
PreparedStatement pstmt = null;
ResultSet rs = null;
String query="SELECT DISTINCT q1,q2,q3 FROM test WHERE (q1,q2,q3) IN (SELECT q1,q2,q3 FROM result)ORDER BY q1,q2,q3 ASC";
try {
con=DatabaseConnection.getConnection();
pstmt = con.prepareStatement(query);
rs = pstmt.executeQuery();
ResultSetMetaData rsmd = (ResultSetMetaData) rs.getMetaData();
columnsNumber = rsmd.getColumnCount();
System.out.println(columnsNumber);
}
catch (Exception e) {
System.out.println("exception in DAO");
}
return columnsNumber;
}
}
表1 :测试
列:id,q1,q2,q3值:1,A,C,C
表2 :结果
列:id,q1,q2,q3值:1,A,B,C
我正在使用此代码,但将值获取为null
公共类ResultDAO {
public String correctAnswer() throws Exception {
String columnsNumber = null;
Connection con=null;
PreparedStatement pstmt = null;
ResultSet rs = null;
String query="SELECT test.id,IF (test.q1 = result.q1, test.q1, NULL) as q1,IF (test.q2 = result.q2, test.q2, NULL) as q2,IF (test.q3 = result.q3, test.q3, NULL) as q3,(test.q1 = result.q1) + (test.q2 = result.q2) + (test.q3 = result.q3) as matchedColumns FROM test INNER JOIN result USING (id) ORDER BY q1,q2,q3";
try {
con=DatabaseConnection.getConnection();
pstmt = con.prepareStatement(query);
rs = pstmt.executeQuery();
System.out.println(rs.next());
while(rs.next()){
columnsNumber=rs.getString("matchedColumns");
}
System.out.println(columnsNumber);
}
catch (Exception e) {
System.out.println("exception in DAO");
}
return columnsNumber;
}
}
请尝试此sqlFiddle
SELECT test.id,
IF (test.q1 = result.q1, test.q1, NULL) as q1,
IF (test.q2 = result.q2, test.q2, NULL) as q2,
IF (test.q3 = result.q3, test.q3, NULL) as q3,
(test.q1 = result.q1) + (test.q2 = result.q2) + (test.q3 = result.q3) as matchedColumns
FROM test
INNER JOIN result
USING (id)
ORDER BY q1,q2,q3
编辑:要获取不匹配的列,只需将=
符号更改为!=
然后添加另一个名为unmatchedColumns sqlFiddle的已创建列
SELECT test.id,
IF (test.q1 = result.q1, test.q1, NULL) as q1,
IF (test.q2 = result.q2, test.q2, NULL) as q2,
IF (test.q3 = result.q3, test.q3, NULL) as q3,
(test.q1 = result.q1) + (test.q2 = result.q2) + (test.q3 = result.q3) as matchedColumns,
(test.q1 != result.q1) + (test.q2 != result.q2) + (test.q3 != result.q3) as unmatchedColumns
FROM test
INNER JOIN result
USING (id)
ORDER BY q1,q2,q3
我假设id是结果表中的外键
select tst.id,tst.q1,tst.q2,tst.q3,
r.id,r.q1,r.q2,r.q3
from test as tst
LEFT JOIN result AS r
ON tst.id = r.id
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