Question

查询：

SELECT DISTINCT UNIQUEID,ID
FROM
(
  (SELECT UNIQUEID, DATE, ID
     FROM stackscontents
    WHERE BACKGROUND IS NOT NULL 
      AND TITLE IS NOT NULL 
      AND ID < ?
    ORDER BY DATE DESC limit 1)
   UNION ALL
   (SELECT UNIQUEID, DATE, ID
      FROM stackscontents 
      WHERE BACKGROUND IS NOT NULL
        AND TITLE IS NOT NULL
        AND ID > ?
      ORDER BY DATE ASC limit 1)
)
UNION ALL (
  (SELECT UNIQUEID, DATE, ID
     FROM sharedlinks 
    WHERE ID < ?
    ORDER BY DATE DESC limit 1)
  UNION ALL
  (SELECT UNIQUEID, DATE, ID
     FROM sharedlinks
    WHERE ID > ? 
    ORDER BY DATE ASC limit 1)
) t

准确地说，我正在尝试从2个表中获取一行。但是我收到如下语法错误：

com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException：每个派生表必须具有自己的别名

以下是我使用查询的代码：

if (NewDetails == null) {

        query2 = "SELECT DISTINCT UNIQUEID,ID FROM ((SELECT UNIQUEID, DATE, ID FROM stackscontents WHERE BACKGROUND IS NOT NULL AND TITLE IS NOT NULL AND ID < ? ORDER BY DATE DESC limit 1) UNION ALL (SELECT UNIQUEID, DATE, ID FROM stackscontents WHERE BACKGROUND IS NOT NULL AND TITLE IS NOT NULL ID > ? ORDER BY DATE ASC limit 1)) UNION ALL "
        + "((SELECT UNIQUEID, DATE, ID FROM sharedlinks WHERE ID < ? ORDER BY DATE DESC limit 1) UNION ALL (SELECT UNIQUEID, DATE, ID FROM sharedlinks WHERE ID > ? ORDER BY DATE ASC limit 1)) t ";

    try {
        DBConnect Database = new DBConnect();
        Connection con = null;
        PreparedStatement ps = null;
        ResultSet rs = null;

        try {
            con = Database.getcon();
            ps = con.prepareStatement(query2);
            ps.setInt(1, minID);
            ps.setInt(2, minID);
            ps.setInt(3, minID);
            ps.setInt(4, minID);
            rs=ps.executeQuery();

            while(rs.next()) {
                minID = rs.getInt(2);
                parts[i] = rs.getString(1);
                i--;
            }
        } finally {
            if (ps != null)
                ps.close();
            if (rs != null)
                rs.close();
            if (con != null)
                con.close();
        }
    } catch (SQLException e) {
        e.printStackTrace();
    }                       
}

不幸的是，它也没有返回预期的行-1，但是它从第一行stackscontents返回451。如下：

Stackscontents：

Texture2D.Apply()

共享链接：

stackscontents table rows

Answer 1

您的括号使事情变得混乱。重新格式化您的代码以显示原因：

 SELECT DISTINCT UNIQUEID,ID
 FROM (
        (SELECT UNIQUEID, DATE, ID FROM stackscontents WHERE BACKGROUND IS NOT NULL AND TITLE IS NOT NULL AND ID < ? ORDER BY DATE DESC limit 1)
       UNION ALL
        (SELECT UNIQUEID, DATE, ID FROM stackscontents WHERE BACKGROUND IS NOT NULL AND TITLE IS NOT NULL AND ID > ? ORDER BY DATE ASC limit 1)
      )
UNION ALL
      (
        (SELECT UNIQUEID, DATE, ID FROM sharedlinks WHERE ID < ? ORDER BY DATE DESC limit 1)
       UNION ALL
        (SELECT UNIQUEID, DATE, ID FROM sharedlinks WHERE ID > ? ORDER BY DATE ASC limit 1)
      ) t

难怪SQL解析器会显示“嗯？”

您的代码应为：

 SELECT DISTINCT UNIQUEID,ID
 FROM (
        (SELECT UNIQUEID, DATE, ID FROM stackscontents WHERE BACKGROUND IS NOT NULL AND TITLE IS NOT NULL AND ID < ? ORDER BY DATE DESC limit 1)
       UNION ALL
        (SELECT UNIQUEID, DATE, ID FROM stackscontents WHERE BACKGROUND IS NOT NULL AND TITLE IS NOT NULL AND ID > ? ORDER BY DATE ASC limit 1)
       UNION ALL
        (SELECT UNIQUEID, DATE, ID FROM sharedlinks WHERE ID < ? ORDER BY DATE DESC limit 1)
       UNION ALL
        (SELECT UNIQUEID, DATE, ID FROM sharedlinks WHERE ID > ? ORDER BY DATE ASC limit 1)
     ) t

如何从两个表SQL中选择一行在另一行之前？

1 个答案: