PHP / MySQL - 构建查询

Question

我试图整理一个SQL查询，它让我感到困惑，我用正常语言写出了我需要的东西，我似乎无法得到它。

select * from introles where introle = $key 
then check the table 'availability' for the user_id taken from the introles table
then out of those results, check that $_POST['date'] is not equal to the date in the 'availability' table

任何帮助都会令人惊讶：）

编辑：表格结构如下

表格介绍有以下内容

id
user_id
introle

表可用性具有以下内容

id
user_id
date

Answer 1

你可以尝试

吗？

'$variable'

而不是

 $variable

对于sql查询中的所有变量？

Answer 2

$query = "SELECT a.id AS aId, i.id AS iId, a.user_id, introle, date FROM availability AS a, introle AS i WHERE date != {$_POST['date']} AND a.user_id IN (SELECT user_id FROM introle WHERE introle = {$key})";