更新 MySql 字段（如果字段不为空，则转到下一个）

Question

您好，我有 10 列的表（columnA、ColumnB、ColumnC ...），ColumnA 用于 ID。

我想以这种方式在 php 中进行更新：如果 ColumnB 不为空，则更新 ColumnC，如果 ColumnC 不为空，则更新 ColumnD ...直到找到一个空列。 p>

我知道如何更新一个空列，但我不知道如何实现 IF 语句。

到目前为止，我有这个：

mysql_query("UPDATE tabel_name SET ColumnB = 'example' WHERE ColumnA = '$ID' "); 

谢谢

Answer 1

您必须使用case 仅更新选择性列。

示例：

update table_name set  
    col1 = ( case when col1 is null then ? else col1 end )  
    , col2 = ( case when col2 is null then ? else col2 end )  
--  , col3 = ...
;

使用mysql prepare 替换查询参数。

另请参阅Quassnoi's answer to a similar posting。

更新：

如果 ColumnB 不为空，则更新 ColumnC，如果 ColumnC 不为空，则更新 ColumnD ...直到找到一个空列。

您需要以相反的顺序设置列值检查。

update table_name set  
--      more next ( 4 to n ) columns here if required       
    col3 = ( case when ( col2 is not null and col3 is null ) then 7 else col3 end )  
    , col2 = ( case when ( col1 is not null and col2 is null ) then 8 else col2 end )  
    , col1 = ( case when ( col1 is null ) then 9 else col1 end )  
;

示例表：

mysql> create table col_values ( id INT, col1 INT, col2 INT, col3 INT );
Query OK, 0 rows affected (0.06 sec)

mysql> insert into col_values values ( 1, 1, 1, NULL ), ( 2, 1, NULL, NULL ), ( 3, NULL, NULL, NULL );
Query OK, 3 rows affected (0.01 sec)
Records: 3  Duplicates: 0  Warnings: 0

mysql> select * from col_values;
+------+------+------+------+
| id   | col1 | col2 | col3 |
+------+------+------+------+
|    1 |    1 |    1 | NULL |
|    2 |    1 | NULL | NULL |
|    3 | NULL | NULL | NULL |
+------+------+------+------+
3 rows in set (0.00 sec)

mysql> update col_values set
    ->     col3 = ( case when ( col2 is not NULL and col3 is NULL ) then 7 else col3 end )
    ->     , col2 = ( case when ( col1 is not NULL and col2 is NULL ) then 8 else col2 end )
    ->     , col1 = ( case when ( col1 is NULL ) then 9 else col1 end )
    -> ;
Query OK, 3 rows affected (0.02 sec)
Rows matched: 3  Changed: 3  Warnings: 0

mysql> select * from col_values;
+------+------+------+------+
| id   | col1 | col2 | col3 |
+------+------+------+------+
|    1 |    1 |    1 |    7 |
|    2 |    1 |    8 | NULL |
|    3 |    9 | NULL | NULL |
+------+------+------+------+
3 rows in set (0.00 sec)

您也可以使用if 函数来替代case 语句。

mysql> truncate table col_values;
Query OK, 3 rows affected (0.01 sec)

mysql> insert into col_values values ( 1, 1, 1, NULL ), ( 2, 1, NULL, NULL ), ( 3, NULL, NULL, NULL );
Query OK, 3 rows affected (0.02 sec)
Records: 3  Duplicates: 0  Warnings: 0

mysql> select * from col_values;
+------+------+------+------+
| id   | col1 | col2 | col3 |
+------+------+------+------+
|    1 |    1 |    1 | NULL |
|    2 |    1 | NULL | NULL |
|    3 | NULL | NULL | NULL |
+------+------+------+------+
3 rows in set (0.00 sec)

mysql> update col_values set
    ->     col3 = if( ( col2 is not NULL and col3 is NULL ), 7, col3 )
    ->     , col2 = if( ( col1 is not NULL and col2 is NULL ), 8, col2 )
    ->     , col1 = if( col1 is NULL, 9, col1 )
    -> ;
Query OK, 3 rows affected (0.01 sec)
Rows matched: 3  Changed: 3  Warnings: 0

mysql> select * from col_values;
+------+------+------+------+
| id   | col1 | col2 | col3 |
+------+------+------+------+
|    1 |    1 |    1 |    7 |
|    2 |    1 |    8 | NULL |
|    3 |    9 | NULL | NULL |
+------+------+------+------+
3 rows in set (0.00 sec)

Answer 2

你可以这样做

UPDATE table SET columnC = IF(columnB is not null, "value", columnC) where id = 1

Answer 3

你可以试试这样的：

    $result=mysql_query('SELECT fav1, fav2, fav3, fav4, fav5 FROM users where id=".."');

    $row = mysql_fetch_array($result);

      foreach ($row as $columnName=>$value)
      {
         if ($value==null)
            {
             //update users set $columnName=pageID 
             break;
            }
      }