MySql如何在if语句中结合2个查询(MySql how to union 2 queries within if statements)

 这里我的表单和mysql / php代码。 
 
 如果两个复选框都被选中，则mysql不会执行查询。 有没有办法让这个表格正常工作？ 
 
 MySQL的 
 
 if (isset($_POST['A']) && !empty($_POST['A'])) {
 $query= "SELECT * FROM (SELECT * FROM myTable WHERE...) as A WHERE Column1='y'";
 }
 if (isset($_POST['B']) && !empty($_POST['B'])) {
 $query= "SELECT * FROM (SELECT * FROM myTable WHERE...) as B WHERE Column2='y'";
 }
 
 形成 
 
<form id="myform1" class="myform1" method="post" name="myform1">
<input type="checkbox" name="A[]" id="A" value="y" />
<input type="checkbox" name="B[]" id="B" value="y" />
<input id="submit" type="submit" name="submit" value="Submit" 
onclick="return submitForm1()" />
</form>
 
 任何帮助赞赏。 谢谢 

Here my form and the mysql/php code. 
 
if the 2 checkboxes are both checked mysql doesn't execute the queries. Is there any way to have this form working properly?
 
MySQL
 
 if (isset($_POST['A']) && !empty($_POST['A'])) {
 $query= "SELECT * FROM (SELECT * FROM myTable WHERE...) as A WHERE Column1='y'";
 }
 if (isset($_POST['B']) && !empty($_POST['B'])) {
 $query= "SELECT * FROM (SELECT * FROM myTable WHERE...) as B WHERE Column2='y'";
 }
 
Form
 
<form id="myform1" class="myform1" method="post" name="myform1">
<input type="checkbox" name="A[]" id="A" value="y" />
<input type="checkbox" name="B[]" id="B" value="y" />
<input id="submit" type="submit" name="submit" value="Submit" 
onclick="return submitForm1()" />
</form>
 
Any help appreciated. Thank you

原文：https://stackoverflow.com/questions/17956292