(PHP 5, PHP 7, PHP 8)
mysqli_stmt::result_metadata -- mysqli_stmt_result_metadata — Returns result set metadata from a prepared statement
面向对象风格
过程化风格
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.
注意:
This result set pointer can be passed as an argument to any of the field-based functions that process result set metadata, such as:
The result set structure should be freed when you are done with it, which you can do by passing it to mysqli_free_result()
注意:
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().
Returns a result object or false if an error occurred.
If mysqli error reporting is enabled (MYSQLI_REPORT_ERROR) and the requested operation fails,
a warning is generated. If, in addition, the mode is set to MYSQLI_REPORT_STRICT,
a mysqli_sql_exception is thrown instead.
示例 #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();
?>示例 #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);
?>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.