问题

如果表已经存在，您的代码仍将尝试执行以下查询：

1) ALTER TABLE wp_voicemail_call CHANGE COLUMN user_id user_id BIGINT(9) UNSIGNED NOT NULL
2) ALTER TABLE wp_voicemail_call CHANGE COLUMN call_id call_id BIGINT(9) UNSIGNED NOT NULL
3) ALTER TABLE wp_voicemail_call CHANGE COLUMN opened opened BOOL DEFAULT 0 NOT NULL
4) ALTER TABLE wp_voicemail_call ADD 
5) ALTER TABLE wp_voicemail_call ADD PRIMARY KEY (user_id, call_id)

请注意，此查询：

ALTER TABLE wp_voicemail_call ADD PRIMARY KEY (user_id, call_id)

正在尝试添加另一个已定义的主键，我们只能使用其中一个。因此出现了错误。

此查询：

ALTER TABLE wp_voicemail_call ADD

来自empty line 高于PRIMARY KEY 线

在dbDelta() 功能有this part 这将取消主要部分的设置：

foreach ( $index_strings as $index_string ) {
    if ( ! ( ( $aindex = array_search( $index_string, $indices ) ) === false ) ) {
        unset( $indices[ $aindex ] );
        break
     }
}

但由于某些原因，在您的情况下，数组搜索总是返回false。

我挖得更深，在你的情况下$indices 阵列为：

Array
(
    [0] => 
    [1] => PRIMARY KEY  (user_id, call_id)
)

但是$index_strings 数组为

Array
(
    [0] => PRIMARY KEY  (user_id,call_id)
    [1] => PRIMARY KEY  (user_id,call_id)
)

因此，我们可以看到不匹配：

PRIMARY KEY  (user_id,call_id) 

对

PRIMARY KEY  (user_id, call_id)

。。。单一空间！！

建议的解决方案是，如果我们删除多余的空行和多余的空间：

$sql = "CREATE TABLE {$wpdb->prefix}voicemail_call (
    user_id BIGINT(9) UNSIGNED NOT NULL,
    call_id BIGINT(9) UNSIGNED NOT NULL,
    opened BOOL DEFAULT 0 NOT NULL,
    PRIMARY KEY  (user_id,call_id)
);";

那么我们应该只运行这些查询dbDelta():

1) ALTER TABLE wp_voicemail_call CHANGE COLUMN user_id user_id BIGINT(9) UNSIGNED NOT NULL
2) ALTER TABLE wp_voicemail_call CHANGE COLUMN call_id call_id BIGINT(9) UNSIGNED NOT NULL
3) ALTER TABLE wp_voicemail_call CHANGE COLUMN opened opened BOOL DEFAULT 0 NOT NULL

当表已存在时。