MySQL,用SQL检查表中是否有列

这对我很有效。

SHOW COLUMNS FROM `table` LIKE 'fieldname';

用PHP它会像。。。

$result = mysql_query("SHOW COLUMNS FROM `table` LIKE 'fieldname'");
$exists = (mysql_num_rows($result))?TRUE:FALSE;

@胡里奥

SELECT * 
FROM information_schema.COLUMNS 
WHERE 
    TABLE_SCHEMA = 'db_name' 
AND TABLE_NAME = 'table_name' 
AND COLUMN_NAME = 'column_name'

对我有用。

为了帮助那些正在寻找@Mchl所描述内容的具体示例的人,可以尝试以下方法

 SELECT * FROM information_schema.COLUMNS 
 WHERE TABLE_SCHEMA = 'my_schema' AND TABLE_NAME = 'my_table' 
 AND COLUMN_NAME = 'my_column'`

如果它返回false(零结果),那么您就知道该列不存在。

delimiter //
-- ------------------------------------------------------------
-- Use the inforamtion_schema to tell if a field exists.
-- Optional param dbName, defaults to current database
-- ------------------------------------------------------------
CREATE PROCEDURE fieldExists (
OUT _exists BOOLEAN,      -- return value
IN tableName CHAR(255),   -- name of table to look for
IN columnName CHAR(255),  -- name of column to look for
IN dbName CHAR(255)       -- optional specific db
) BEGIN
-- try to lookup db if none provided
SET @_dbName := IF(dbName IS NULL, database(), dbName);

IF CHAR_LENGTH(@_dbName) = 0
THEN -- no specific or current db to check against
  SELECT FALSE INTO _exists;
ELSE -- we have a db to work with
  SELECT IF(count(*) > 0, TRUE, FALSE) INTO _exists
  FROM information_schema.COLUMNS c
  WHERE 
  c.TABLE_SCHEMA    = @_dbName
  AND c.TABLE_NAME  = tableName
  AND c.COLUMN_NAME = columnName;
END IF;
END //
delimiter ;

使用 fieldExists

mysql> call fieldExists(@_exists, 'jos_vm_product', 'child_option', NULL) //
Query OK, 0 rows affected (0.01 sec)

mysql> select @_exists //
+----------+
| @_exists |
+----------+
|        0 |
+----------+
1 row in set (0.00 sec)

mysql> call fieldExists(@_exists, 'jos_vm_product', 'child_options', 'etrophies') //
Query OK, 0 rows affected (0.01 sec)

mysql> select @_exists //
+----------+
| @_exists |
+----------+
|        1 |
+----------+

下面是另一种使用普通PHP而不使用信息模式数据库的方法:

$chkcol = mysql_query("SELECT * FROM `my_table_name` LIMIT 1");
$mycol = mysql_fetch_array($chkcol);
if(!isset($mycol['my_new_column']))
  mysql_query("ALTER TABLE `my_table_name` ADD `my_new_column` BOOL NOT NULL DEFAULT '0'");

只从信息模式中选择列名称,并将此查询的结果放入变量中。然后测试变量以确定表是否需要更改。

另外,不要忘记为列表指定表\模式。

mysql_query("select $column from $table") or mysql_query("alter table $table add $column varchar (20)");

如果您已经连接到数据库,它就可以工作。

public function GetTableColumn() {      
$query  = $this->db->prepare("SHOW COLUMNS FROM `what_table` LIKE 'what_column'");  
try{            
    $query->execute();                                          
    if($query->fetchColumn()) { return 1; }else{ return 0; }
    }catch(PDOException $e){die($e->getMessage());}     
}

非常感谢Mfoo,他提供了一个非常好的脚本,可以在表中不存在列的情况下动态添加列。 . 这个 脚本还可以帮助您找到实际需要多少表“Add column” mysql公司。尝尝菜谱。很有魅力。

<?php
ini_set('max_execution_time', 0);

$host = 'localhost';
$username = 'root';
$password = '';
$database = 'books';

$con = mysqli_connect($host, $username, $password);
if(!$con) { echo "Cannot connect to the database ";die();}
mysqli_select_db($con, $database);
$result=mysqli_query($con, 'show tables');
$tableArray = array();
while($tables = mysqli_fetch_row($result)) 
{
     $tableArray[] = $tables[0];    
}

$already = 0;
$new = 0;
for($rs = 0; $rs < count($tableArray); $rs++)
{
    $exists = FALSE;

    $result = mysqli_query($con, "SHOW COLUMNS FROM ".$tableArray[$rs]." LIKE 'tags'");
    $exists = (mysqli_num_rows($result))?TRUE:FALSE;

    if($exists == FALSE)
    {
        mysqli_query($con, "ALTER TABLE ".$tableArray[$rs]." ADD COLUMN tags VARCHAR(500) CHARACTER SET utf8 COLLATE utf8_unicode_ci NULL");
        ++$new;
        echo '#'.$new.' Table DONE!<br/>';
    }
    else
    {
        ++$already;
        echo '#'.$already.' Field defined alrady!<br/>';    
    }
    echo '<br/>';
}
?>

只需在表上运行SELECT*查询并检查列是否存在。。。