PDOStatement::fetch()

(PHP 5 >= 5.1.0, PHP 7, PECL pdo >= 0.1.0)

从结果集中获取下一行

说明

从一个 PDOStatement 对象相关的结果集中获取下一行。$fetch_style参数决定 POD 如何返回行。

参数

控制下一行如何返回给调用者。此值必须是PDO::FETCH_*系列常量中的一个，缺省为PDO::ATTR_DEFAULT_FETCH_MODE的值（默认为PDO::FETCH_BOTH）。

• PDO::FETCH_ASSOC：返回一个索引为结果集列名的数组

• 

  PDO::FETCH_BOTH（默认）：返回一个索引为结果集列名和以0开始的列号的数组

• PDO::FETCH_BOUND：返回TRUE，并分配结果集中的列值给PDOStatement::bindColumn()方法绑定的 PHP 变量。

• PDO::FETCH_CLASS：返回一个请求类的新实例，映射结果集中的列名到类中对应的属性名。如果$fetch_style包含 PDO::FETCH_CLASSTYPE（例如：PDO::FETCH_CLASS | PDO::FETCH_CLASSTYPE），则类名由第一列的值决定

• PDO::FETCH_INTO：更新一个被请求类已存在的实例，映射结果集中的列到类中命名的属性

• PDO::FETCH_LAZY：结合使用PDO::FETCH_BOTH和PDO::FETCH_OBJ，创建供用来访问的对象变量名

• PDO::FETCH_NUM：返回一个索引为以0开始的结果集列号的数组

• PDO::FETCH_OBJ：返回一个属性名对应结果集列名的匿名对象

对于一个 PDOStatement 对象表示的可滚动游标，该值决定了哪一行将被返回给调用者。此值必须是PDO::FETCH_ORI_*系列常量中的一个，默认为PDO::FETCH_ORI_NEXT。要想让 PDOStatement 对象使用可滚动游标，必须在用PDO::prepare()预处理SQL语句时，设置PDO::ATTR_CURSOR属性为PDO::CURSOR_SCROLL。

对于一个cursor_orientation参数设置为PDO::FETCH_ORI_ABS的PDOStatement 对象代表的可滚动游标，此值指定结果集中想要获取行的绝对行号。

对于一个cursor_orientation参数设置为PDO::FETCH_ORI_REL的PDOStatement 对象代表的可滚动游标，此值指定想要获取行相对于调用PDOStatement::fetch()前游标的位置

返回值

此函数（方法）成功时返回的值依赖于提取类型。在所有情况下，失败都返回FALSE。

范例

使用不同的提取方式获取行

以上例程会输出：

PDO::FETCH_ASSOC: Return next row as an array indexed by column name
Array
(
    [NAME] => apple
    [COLOUR] => red
)
PDO::FETCH_BOTH: Return next row as an array indexed by both column name and number
Array
(
    [NAME] => banana
    [0] => banana
    [COLOUR] => yellow
    [1] => yellow
)
PDO::FETCH_LAZY: Return next row as an anonymous object with column names as properties
PDORow Object
(
    [NAME] => orange
    [COLOUR] => orange
)
PDO::FETCH_OBJ: Return next row as an anonymous object with column names as properties
kiwi

使用一个可滚动游标获取行

以上例程会输出：

Reading forwards:
21    10    5
16    0     5
19    20    10
Reading backwards:
19    20    10
16    0     5
21    10    5

参见

• PDO::prepare() 准备要执行的语句，并返回语句对象
• PDOStatement::execute() 执行一条预处理语句
• PDOStatement::fetchAll() 返回一个包含结果集中所有行的数组
• PDOStatement::fetchColumn() 从结果集中的下一行返回单独的一列。
• PDOStatement::fetchObject() 获取下一行并作为一个对象返回。
• PDOStatement::setFetchMode() 为语句设置默认的获取模式。

WARNING:
fetch() does NOT adhere to SQL-92 SQLSTATE standard when dealing with empty datasets.
Instead of setting the errorcode class to 20 to indicate "no data found", it returns a class of 00 indicating success, and returns NULL to the caller.
This also prevents the exception mechainsm from firing.
Programmers will need to explicitly code tests for empty resultsets after any fetch*() instead of relying on the default behavior of the RDBMS.
I tried logging this as a bug, but it was dismissed as "working as intended". Just a head's up.

If no record, this function will also return false.
I think that is not very good...

When using PDO::FETCH_COLUMN in a while loop, it's not enough to just use the value in the while statement as many examples show:

If there are 5 rows with values 1 2 0 4 5, then the while loop above will stop at the third row printing only 1 2. The solution is to either explicitly test for false:

Or use foreach with fetchAll():

Both will correctly print 1 2 0 4 5.

Someone's already pointed out that PDO::CURSOR_SCROLL isn't supported by the SQLite driver. It's also worth noting that it's not supported by the MySQL driver either.
In fact, if you try to use scrollable cursors with a MySQL statement, the PDO::FETCH_ORI_ABS parameter and the offset given to fetch() will be silently ignored. fetch() will behave as normal, returning rows in the order in which they came out of the database.
It's actually pretty confusing behaviour at first. Definitely worth documenting even if only as a user-added note on this page.

When fetching an object, the constructor of the class is called after the fields are populated by default.
PDO::FETCH_PROPS_LATE is used to change the behaviour and make it work as expected - constructor be called _before_ the object fields will be populated with the data.
sample:

http://bugs.php.net/bug.php?id=53394

A quick one liner to get the first entry returned. This is nice for very basic queries.
php

Here is quick note for developers that use the PDO SQLite Driver:
The PDO SQLite driver does not support cursors, so using the PDO::CURSOR_SCROLL Attribute, will not work when using the PDO SQLite driver. For example:

What is even worse is that PDO::prepare will NOT throw an Exception when it fails to prepare the query, even when the error mode is set to throw Exceptions, and will instead return a Boolean False!
Not only do I consider this a poor design choice, but also its a real shame that this is not documented anywhere in the manual -- in fact the manual is not clear on what Attributes are supported by which drivers and which are not so developers are left to play a classic game of guess.
I hope this saves some developers some headaches.
Good Luck,

I can also add that the constructor is run _after_ the data is set on the object if yo use PDO::FETCH_CLASS.

Because MySQL does not currently support the use of cursors, the $cursor_offset feature cannot work when using PDO to access a MySQL database.
If you are tring to arbitrarily access a specific record or group of records in a MySQL database recordset, you might want to consider using the LIMIT clause of the SELECT statement to achieve this e.g. LIMIT 5,3 to return just the 6th,7th & 8th records - 3 records starting at index 5 (which is the 6th record).

this is just On reminder note about Second parameter -cursor_oriantation-
PDO::FETCH_ORI_NEXT :-
Fetch the next row in the result set. Valid only for scrollable cursors.
PDO::FETCH_ORI_PRIOR :-
Fetch the previous row in the result set. Valid only for scrollable cursors.
PDO::FETCH_ORI_FIRST :-
Fetch the first row in the result set. Valid only for scrollable cursors.
PDO::FETCH_ORI_LAST :-
Fetch the last row in the result set. Valid only for scrollable cursors.
PDO::FETCH_ORI_ABS :-
Fetch the requested row by row number from the result set. Valid only for scrollable cursors.
PDO::FETCH_ORI_REL :- 
Fetch the requested row by relative position from the current position of the cursor in the result set. Valid only for scrollable cursors.

If you to use a new instance of a class for a record you can use: 

I could use PDO::FETCH_COLUMN to retrieve the first column from result.
$ps->fetch( PDO::FETCH_COLUMN );
Worked on Postgresql with PHP 5.3.10.

If you want to use PDO::FETCH_CLASS you need to set it up with setFetchMode first like so:
    $stmt->setFetchMode( PDO::FETCH_CLASS, 'classType', array( 'parameters to constructor' );
    $object = $stmt->fetch( PDO::FETCH_CLASS );
If you ommit this PHP will segfault.

note that fetch constants are not included in the PDO class for PHP versions prior to 5.1

I spent some hours trying to find out how to manipulate with BLOB fields using PDO.
Remember that you can't retreive BLOB data using something like this :

Instead of this you should try following approach: 

Be careful when using PDO::FETCH_LAZY. It adds an additional field called queryString. I'm not sure if this a bug or not. I'm using version 5.6.17 in Debian Jessie.
Query: 'select 1,2,3'
$row=$smt->fetch(PDO::FETCH_OBJ);
var_dump($row);
object(stdClass)#6 (3) {
 ["1"]=>
 string(1) "1"
 ["2"]=>
 string(1) "2"
 ["3"]=>
 string(1) "3"
}
$row=$smt->fetch(PDO::FETCH_LAZY);
var_dump($row);
object(PDORow)#3 (4) {
 ["queryString"]=>
 string(12) "select 1,2,3"
 ["1"]=>
 string(1) "1"
 ["2"]=>
 string(1) "2"
 ["3"]=>
 string(1) "3"
}

Be careful with fetch() when you use prepared statements and MySQL (I don`t know how it is with other databases). Fetch won`t close cursor and won`t let you send any other query, even if your result set has only one row, . 
If you use $statement->fetch(), you will also have to use $statement->closeCursor() afterwards, to be albe to execute another query.
Alternatively you can use $statement->fetchAll() without $statement->closeCursor().

Note that this way, the "fetch mode" will get "overwritten", and PDO::FETCH_PROPS_LATE won't be applied:

Instead, you should leave the parameter area for the fetch() method empty, like this (if you want to set the fetch mode with the setFetchMode() method): 

It seems that if you do a $statement->query() with an INSERT statement and after that a $statement->fetch() you will get an exception saying: SQLSTATE[HY000]: General error.

Note that PDO::ATTR_STRINGIFY_FETCHES will NOT work for the MySQL driver. MySQL will always return strings because that is the behaviour of the core mysql PHP extension. See http://bugs.php.net/bug.php?id=44341

Note that using the FETCH_CLASS mechanism does NOT trigger the class's constructor! You must explicity instantiate the class to use it's constructor behavior.

Don't do 
if($objStatement->fetch()) return $objStatement->fetch(); 
You want  
if($blah=$objStatement->fetch()) return $blah;
Trust me on this one.

I got problems during fetch of stored procedures with mssql following PDOException:
SQLSTATE[IMSSP]: The active result for the query contains no fields
with a a prepared statement like:
 EXEC [mydb].[stored_procedure_that_returns_select] ?;
The solution was to supress the count of records
SET NOCOUNT ON; EXEC [mydb].[stored_procedure_that_returns_select] ?;
Hope it helps!

When you do a SELECT query for one row, and want to check if it's there, you don't need to count the fetchAll() result, you can just check if $result->fetch() is true: 

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