mysql - 如何在 select 语句中使用 mysql 变量/如何在下一个 select 中使用 'as' 变量

Question

select 
count(invoice.id) as count_invoice_id, // i want to simply use count_invoice_id instead of using count(discount_offer.id) again inside the if statement below
if(count(invoice.id) > 1 , 'true','false') // i want to used count_invoice_id here
from invoice as invoice
left join discount_offer as discount_offer 
on invoice.id = discount_offer.invoice_id;

以上是我的 sql ，如果我想在 if 语句中使用 count_invoice_id 是否可能。目前我所做的是在 invoice.id 列上再次重复计数方法。

我想在上面的 sql 中的 if 语句中将 'count(invoice.id)' 更改为 'count_invoice_id'

Answer 1

您可以使用子查询:

SELECT count_invoice_id, IF(count_invoice_id > 1 , 'true', 'false')
FROM   (SELECT    COUNT(invoice.id) AS count_invoice_id
        FROM      invoice
        LEFT JOIN discount_offer ON invoice.id = discount_offer.invoice_id) t