SQL查詢搜索功能

Question

我想用多個Java Swing組件做一個Search函數，用戶可以在其中搜索（名稱/國籍/專業/經驗），結果將顯示在Jtable中。

我只是在苦苦思索SQL查詢，好像用戶只鍵入了一個'name'，沒有數據會被檢索，因為它會像這樣（name，null，null，null）進入數據庫，而且我沒有任何null我的數據庫中的值。

所以我想要檢索具有該名稱的所有數據而不管其他列，但同時，如果他們也選擇了特定的專業，我想要檢索具有所選名稱和專業的所有數據，依此類推。

我希望你理解我的問題。

我當前的SQL語句：

public ArrayList<Applications> getData(String name, String nationality, String specialty, String experience) {

   ArrayList<Applications> list = new ArrayList<Applications>();
   Connection con = getConnection();
   Statement st;
   ResultSet rows;

   try {
       st = con.createStatement();

       rows = st.executeQuery("SELECT * FROM applications WHERE name LIKE '%" +  name+"%'"
            + " AND (nationality LIKE '" +  nationality+"')"
            + " AND (specialty LIKE '" +  specialty+"')"
            + " AND (experience LIKE '" +  experience+"')");

       Applications applications;

       while(rows.next()) {
           applications = new Applications(
               rows.getInt("id"),
               rows.getString("name"),
               rows.getString("nationality"),
               rows.getString("Specialty"),
               rows.getString("experience")
           );

          list.add(applications);
       }   
   } catch (SQLException ex) {
       Logger.getLogger(MyQuery.class.getName()).log(Level.SEVERE, null, ex);
   }

   return list;
}

Answer 1

讓我們看看你的查詢：

   rows = st.executeQuery("SELECT * FROM applications WHERE name LIKE '%" +  name+"%'"
        + " AND (nationality LIKE '" +  nationality+"')"
        + " AND (specialty LIKE '" +  specialty+"')"
        + " AND (experience LIKE '" +  experience+"')");

這里，由於只給出了name ，其他值為null 。 如果您編寫此代碼用於測試目的：

String foo = null;
System.out.println(foo + "");

輸出將是

“空值”

因此，由於您的值為null ，因此生成的查詢將為

   SELECT * FROM applications WHERE name LIKE '%Rowan Atkinson%'
        AND (nationality LIKE 'null')
        AND (specialty LIKE 'null')
        AND (experience LIKE 'null')

首先，讓我們確保在null情況下得到空String ：

   rows = st.executeQuery("SELECT * FROM applications WHERE name LIKE '%" +  ((name == null) ? "" : name)+"%'"
        + " AND (nationality LIKE '" +  ((nationality == null) ? "" : nationality)+"')"
        + " AND (specialty LIKE '" +  ((specialty == null) ? "" : specialty)+"')"
        + " AND (experience LIKE '" +  ((experience == null) ? "" : experience)+"')");

接下來的問題是你只是在name % ，這也是不正確的，所以讓我們解決這個問題：

   rows = st.executeQuery("SELECT * FROM applications WHERE name LIKE '%" +  ((name == null) ? "" : name)+"%'"
        + " AND (nationality LIKE '%" +  ((nationality == null) ? "" : nationality)+"%')"
        + " AND (specialty LIKE '%" +  ((specialty == null) ? "" : specialty)+"%')"
        + " AND (experience LIKE '%" +  ((experience == null) ? "" : experience)+"%')");

現在閱讀YCF_L的答案，這樣您就可以使用PreparedStatement的命名參數。

Answer 2

下面的代碼可能會給你預期的結果。

StringBuilder sql=new StringBuilder("SELECT * FROM applications WHERE 1=1 ");
        if(!name.isEmpty()){
            sql.append(" AND name LIKE '%" +  name+"%'");
        }
        if(!nationality.isEmpty()){
            sql.append(" AND (nationality LIKE '" +  nationality+"')");
        }
        if(!specialty.isEmpty()){
            sql.append(" AND (specialty LIKE '" +  specialty+"')");
        }
        if(!experience.isEmpty()){
            sql.append(" AND (experience LIKE '" +  experience+"')");
        }

        rows = st.executeQuery(sql.toString());

試試這個

Answer 3

在這種情況下，您有兩個解決方案：

1. 檢查值是否為null將該部分附加到查詢，否則忽略它
2. 第二種解決方案，您可以在查詢中檢查值是否為null。

我將給你一個關於第二個的例子，你可以使用NamedParameterStatement它就像PrepapredStatement來避免語法錯誤和SQL注入：

String query = "SELECT * FROM applications"
        + " WHERE (:name is null or name LIKE CONCAT('%', :name, '%')) "
        + " AND (:nationality is null or nationality LIKE :nationality)"
        + " AND (:specialty is null or specialty LIKE :specialty)"
        + " AND (:experience is null or experience LIKE :experience)";

NamedParameterStatement namedParametterStatement = 
                           new NamedParameterStatement(connection, query);

namedParametterStatement.setString("name", name);
namedParametterStatement.setString("nationality", nationality);
namedParametterStatement.setString("specialty", specialty);
namedParametterStatement.setString("experience", experience);

注意這個例子：

(:nationality is null or nationality LIKE :nationality)

它將檢查nationality是否為空或國籍如你傳遞的價值，這樣你就避免了空。

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一些很好的參考：

• PreparedStatement的命名參數