SQL语句

IF表达式

SELECT IF(sva=1,"男","女") AS s FROM table_name 
WHERE sva != '';

CASE WHEN

SELECT CASE sva
WHEN 1 THEN '男' 
　　ELSE '女' 
END AS s 
FROM table_name
WHERE sva != '';

IFNULL(expr1,expr2)

假如expr1 不为 NULL，则 IFNULL() 的返回值为 expr1; 否则其返回值为 expr2。IFNULL()的返回值是数字或是字符串，具体情况取决于其所使用的语境

select ifnull((SELECT if(service_status='COMPLETED',TRUE,FALSE) as allow_show from es_as_order WHERE order_sn ='2226067809608867869'), 0) as allow_show;