mysqli_stmt::result_metadata()

(PHP 5, PHP 7)

Returns result set metadata from a prepared statement

说明

面向对象风格
mysqli_stmt::result_metadata(void): mysqli_result

过程化风格
mysqli_stmt_result_metadata(mysqli_stmt$stmt): mysqli_result

If a statement passed to mysqli_prepare() is one that produces a result set,mysqli_stmt_result_metadata() returns the result object that can be used to process the meta information such as total number of fields and individual field information.

Note:

This result set pointer can be passed as an argument to any of the field-based functions that process result set metadata, such as:

• mysqli_num_fields()

• mysqli_fetch_field()

• mysqli_fetch_field_direct()

• mysqli_fetch_fields()

• mysqli_field_count()

• mysqli_field_seek()

• mysqli_field_tell()

• mysqli_free_result()

The result set structure should be freed when you are done with it, which you can do by passing it to mysqli_free_result()

Note:

The result set returned by mysqli_stmt_result_metadata() contains only metadata. It does not contain any row results. The rows are obtained by using the statement handle with mysqli_stmt_fetch().

参数

$stmt

仅以过程化样式：由mysqli_stmt_init()返回的 statement 标识。

返回值

Returns a result object or FALSE if an error occurred.

范例

Example #1 面向对象风格

<?php
$mysqli = new mysqli("localhost", "my_user", "my_password", "test");
$mysqli->query("DROP TABLE IF EXISTS friends");
$mysqli->query("CREATE TABLE friends (id int, name varchar(20))");
$mysqli->query("INSERT INTO friends VALUES (1,'Hartmut'), (2, 'Ulf')");
$stmt = $mysqli->prepare("SELECT id, name FROM friends");
$stmt->execute();
/* get resultset for metadata */
$result = $stmt->result_metadata();
/* retrieve field information from metadata result set */
$field = $result->fetch_field();
printf("Fieldname: %s\n", $field->name);
/* close resultset */
$result->close();
/* close connection */
$mysqli->close();
?>

Example #2 过程化风格

<?php
$link = mysqli_connect("localhost", "my_user", "my_password", "test");
mysqli_query($link, "DROP TABLE IF EXISTS friends");
mysqli_query($link, "CREATE TABLE friends (id int, name varchar(20))");
mysqli_query($link, "INSERT INTO friends VALUES (1,'Hartmut'), (2, 'Ulf')");
$stmt = mysqli_prepare($link, "SELECT id, name FROM friends");
mysqli_stmt_execute($stmt);
/* get resultset for metadata */
$result = mysqli_stmt_result_metadata($stmt);
/* retrieve field information from metadata result set */
$field = mysqli_fetch_field($result);
printf("Fieldname: %s\n", $field->name);
/* close resultset */
mysqli_free_result($result);
/* close connection */
mysqli_close($link);
?>

参见

• mysqli_prepare() 准备执行一个 SQL 语句
• mysqli_free_result() Frees the memory associated with a result

If result_metadata() returns false but error/errno/sqlstate tells you no error occurred, this means your query is one that does not produce a result set, i.e. an INSERT/UPDATE/DELETE query instead of a SELECT query.
This is stated in the documentation where it says "If a statement passed to mysqli_prepare() is one that produces a result set, mysqli_stmt_result_metadata() returns the result object", but it might not be clear to everyone what this entails exactly. 
Hope this helps.