Is this method of operation on the database is safe and correct?

 if(isset($_POST['name'])){

    $table = $wpdb->prefix.'_my_table';

    $post = trim(sanitize_user($_POST['name'], true));

    $part = $this->wpdb->prepare("WHERE name = %s", $post)

    $results = $this->wpdb->get_results("SELECT * FROM {$table} $part", ARRAY_A)

  }

Is this method of operation on the database is safe and correct?

 if(isset($_POST['name'])){

    $table = $wpdb->prefix.'_my_table';

    $post = trim(sanitize_user($_POST['name'], true));

    $part = $this->wpdb->prepare("WHERE name = %s", $post)

    $results = $this->wpdb->get_results("SELECT * FROM {$table} $part", ARRAY_A)

  }

• plugins
• query
• sql

2 Answers 2

What you're doing is safe.

However, some notes:

1. See the WP_User_Query class in the Codex. This is the, "official," way to do something like this, although you'll get an integer-indexed array of WP_User objects. Instead of the ARRAY_A that you've specified.
2. You probably don't want _my_table, unless your table is called something like wp__my_table (note the double underscore after wp). The prefix returned from $wpdb->prefix includes the underscore that many installations use after the prefix.
3. The trim() call after sanitize_user() is superfluous. It doesn't hurt anything but it's also a waste of compute cycles.
4. You may be able to write this in one line: $results = $wpdb->get_results($wpdb->prepare("select * from {$wpdb->prefix}my_table where name = %s", sanitize_user($_POST['name'])), ARRAY_A); This may be better or worse for you.

It's close. There's a few things that stand out.

First, I assume you're doing this before the code you shared. It's important to verify a nonce before accepting user input. Read more about Nonce in the Codex.

Next, you want to use sanitize_text_field in combination with wp_unslash. Trim is more of a helper function than for sanitizing, but it's helpful here to ensure expected results.

Finally, combine your entire SQL query in $wpdb->prepare(). Remember $wpdb->prefix usually includes an underscore. Your code would produce wp__my_table, for example (2 underscores).

Note: I changed $this->wpdb to the global $wpdb. This is probably unnecessary for you, but I wanted to make sure others that landed on this answer had the right context. I also changed the table name to posts and the name to title for testing.

if ( isset( $_POST['name'] ) ) {
    global $wpdb;
    $post_name = sanitize_text_field( wp_unslash( trim( $_POST['name'] ) ) ) );

    $sql = $wpdb->prepare( "SELECT * FROM {$wpdb->prefix}posts WHERE post_title = %s", $post_name );

    $results = $wpdb->get_results( $sql, ARRAY_A );
}

For more information on WordPress coding standards for sanitizing input data, check out The WordPress Coding Standards.