sql - Postgresql 根据条件计数

Question

我正在执行这个查询

SELECT COUNT(designer_orders.id) as pr, 
       SUM(IF designer_orders.package_status == 'packed' THEN 0 ELSE 1 END) as pu 
FROM "designer_orders"

预期输出

PR PU10 5

Getting Output

PR PU10 0

This block of query not working as expected

SUM(IF designer_orders.package_status == 'packed' THEN 0 ELSE 1 END)

Answer 1

SQL中没有IF，需要使用CASE。

此外，SQL 中的相等运算符是 = 而不是 ==

SELECT COUNT(id) as pr, 
       SUM(CASE WHEN package_status = 'packed' THEN 0 ELSE 1 END) as pu 
FROM designer_orders;

有关SQL的介绍，请参阅本手册的这一章:http://www.postgresql.org/docs/current/static/tutorial-sql.html

有关可用运算符的说明，请参阅此处:http://www.postgresql.org/docs/current/static/functions-conditional.html