（JDBC）使用if语句和多个条件的Mysql查询

Question

mysql-java语句的正确语法是什么，例如这个？

PreparedStatement st =connection.prepareStatement("SELECT Name, Value, Quantity FROM sales if (type=='Purchase' AND state=='confirmed') OR (type=='Sale' AND state=='not confirmed'))  ; 

Answer 1

SQL看起来像：

SELECT Name, Value, Quantity
FROM sales 
WHERE (type = 'Purchase' AND state = 'confirmed') OR
      (type = 'Sale' AND state = 'not confirmed');

Answer 2

如果where clause, not an = clause, and the equality check operator in SQL is ==`，条件应为, not。所以：

SELECT Name, Value, Quantity 
FROM   sales 
WHERe  (type = 'Purchase' AND state = 'confirmed') OR 
       (type = 'Sale' AND state = 'not confirmed')