双引号内的变量 [英] Variable within double quotes

问题描述

哪个是正确的语法?

$current_renewal_date = $wpdb->get_results(
                    "
                    SELECT expiry_date
                    FROM bid_tag
                    WHERE id = $renewal_tag_id
                    LIMIT 1
                    "
                );

或

$current_renewal_date = $wpdb->get_results(
                    "
                    SELECT expiry_date
                    FROM bid_tag
                    WHERE id = {$renewal_tag_id}
                    LIMIT 1
                    "
                );

推荐答案

两者都是正确的.后者只是用来避免歧义，就像你想引用 $foo 而不是 $foobar:

Both are correct. The latter is just used to avoid ambiguity like if you want to reference $foo and not $foobar:

"{$foo}bar"

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