sql中如何进行if_else判断?

Question

左连接查询

SELECT customers.c_id,orders.o_num
FROM customers 
LEFT OUTER JOIN orders
on customers.c_id = orders.c_id

有链接查询

SELECT customers.c_id,orders.o_num
FROM customers 
RIGHT OUTER JOIN orders
on customers.c_id = orders.c_id

如何在一条sql中实现满足条件就左连接查询

不满足就右连接查询,下面测试不通过

SELECT customers.c_id,orders.o_num
FROM customers 
CASE WHEN 1>0 THEN
        LEFT OUTER JOIN orders
    ELSE
        RIGHT OUTER JOIN orders
END
on customers.c_id = orders.c_id

Answer 1

1、建议写两个sql语句然后这种判断在程序里面实现，

2、只见过查询结果里面使用这种case when 判断语法的

3、你这种条件的动态拼接属于动态sql，一般是存储过程中的概念