SQL 逻辑中的 Java 插入或更新

Question

我有一个表格，如下所示:

mysql> select *  from category;
+-------------+----------+------+------+------+------+------+------+------+------+------+-----------------+
| category_id | T1       | T2   | T3   | T4   | T5   | T6   | T7   | T8   | T9   | T10  | vendor_brand_id |
+-------------+----------+------+------+------+------+------+------+------+------+------+-----------------+
|          12 | Popcorn      | rgp  | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | 3000            |

我正在尝试插入一个新行作为爆米花桶，使其看起来像这样:

mysql> select *  from category;
+-------------+----------+------+------+------+------+------+------+------+------+------+-----------------+
| category_id | T1       | T2   | T3   | T4   | T5   | T6   | T7   | T8   | T9   | T10  | vendor_brand_id |
+-------------+----------+------+------+------+------+------+------+------+------+------+-----------------+
|          12 | Popcorn      | rgp  | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | 3000            |
|          13 | Popcorn      | Bucket  | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | 3000            |

但这正在更新现有行。

有人可以告诉我出了什么问题吗？

String vendor_brand_id ="3000";
String reqstr ="Popcorn";
String value="Bucket";

sqlselect = "select category_id  from category where T1 = ? AND T2!=NULL  AND vendor_brand_id = ?";
selectpst = dbConnection.prepareStatement(sqlselect);
selectpst.setString(1, valuess[0]);
selectpst.setString(2, vendor_brand_id);
resultset = selectpst.executeQuery();

if(resultset.next())
{
    sql=    "select category_id   from category where T1 = ? AND T2=?  AND vendor_brand_id = ?";

    selectpst2 = dbConnection.prepareStatement(sql);

    selectpst2.setString(1, valuess[0]);
    selectpst2.setString(2, value);
    selectpst2.setString(3, vendor_brand_id);
    resultset2 = selectpst2.executeQuery();

    if(resultset2.next())
    {

    }
    else
    {
        sql = "Insert into category (T1,T2,T3,T4,T5,T6,T7,T8,T9,T10,vendor_brand_id) values ('"+valuess[0]+"','"+value+"',NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,"+vendor_brand_id+") ";
        updateStatement.executeUpdate(sql);
    }
}
else
{
    sql = "update category set T2 = '"+value+"' where T1 ='"+valuess[0]+"'   AND vendor_brand_id = "+vendor_brand_id+" " ;
    updateStatement.executeUpdate(sql);
}

Answer 1

MySQL 处理 NULL in a rather special manner ;摘自文章:“不能使用 =、< 或 <> 等算术比较运算符来测试 NULL”

尝试更改您的第一个 SELECT 语句:

/* Old */
select category_id  from category where T1 = ? AND T2!=NULL  AND vendor_brand_id = ?

/* New */
SELECT category_id FROM category WHERE T1=? AND T2 IS NOT NULL AND vendor_brand_id=?