Question

我有三个查询，我想将其合并到一个查询中，该查询可以接受WHERE个可变长度的参数;我不记得我的生活如何做到这一点。

PreparedStatement queryOne = connection.prepareStatement
("SELECT columnOne, columnTwo, columnThree FROM tableOne WHERE columnOne = ?;" );

PreparedStatement queryTwo = connection.prepareStatement
("SELECT columnOne, columnTwo, columnThree FROM tableOne WHERE columnTwo = ?;" );

PreparedStatement queryThree = connection.prepareStatement
("SELECT columnOne, columnTwo, columnThree FROM tableOne WHERE columnOne = ? AND columnTwo = ?;" );

Answer 1

所有三个查询都从同一个表中选择相同的列，因此可以在一个语句中轻松完成它们的联合：

SELECT columnOne, columnTwo, columnThree 
  FROM tableOne 
 WHERE columnOne = ?
    or columnTwo = ?
    or (columnOne = ? AND columnTwo = ?)

Answer 2

回答了我自己的问题，请随时了解这是否是不好的做法。

String columnOne = getValue();
String columnTwo = getValue();
String queryString = "SELECT columnOne, columnTwo, columnThree FROM tableOne"

if (columnOne != null && columnTwo != null)
    queryString = queryString + "WHERE columnOne = ? AND columnTwo = ?"
else if (columnOne != null)
    queryString = queryString + "WHERE columnOne = ?"
else if (columnTwo != null)
    queryString = queryString + "WHERE columnTwo = ?"

PreparedStatement query = connection.prepareStatement(queryString);

具有可变参数的简单查询

2 个答案: