Question

我只是SQL的初学者，但我遇到了这个恼人的错误。 SQL遇到此脚本的WHERE子句的问题：

SELECT
  ITEM_ID, ITEM_PRICE, DISCOUNT_AMOUNT, QUANTITY, 
  (ITEM_PRICE*QUANTITY) AS price_total, 
  (DISCOUNT_AMOUNT*QUANTITY) AS discount_total, 
  ((ITEM_PRICE-DISCOUNT_AMOUNT)*QUANTITY) AS item_total
FROM ORDER_ITEMS
WHERE item_total > 500
ORDER BY item_total;

我收到此错误：

Error starting at line : 1 in command -
SELECT 
  ITEM_ID, ITEM_PRICE, DISCOUNT_AMOUNT, QUANTITY,  
  (ITEM_PRICE*QUANTITY) AS price_total,  
  (DISCOUNT_AMOUNT*QUANTITY) AS discount_total,  
  ((ITEM_PRICE-DISCOUNT_AMOUNT)*QUANTITY) AS item_total 
FROM ORDER_ITEMS 
WHERE item_total > 500 
ORDER BY item_total DESC;
Error at Command Line : 7 Column : 7
Error report -
SQL Error: ORA-00904: "ITEM_TOTAL": invalid identifier
00904. 00000 -  "%s: invalid identifier"
*Cause:    
*Action:

我不知道为什么它与price_total和discount_total没有问题，但是报告item_total无效。我试图在减去折扣金额时首先仅选择总数大于500的项目，并将其乘以数量。然后，我需要按item_total

按降序对结果进行排序

Answer 1

可以在查询选择列表中使用别名为列提供不同的名称。您可以在GROUP BY，ORDER BY或HAVING中使用别名   条款引用该栏目。

标准SQL不允许在WHERE子句中引用列别名。强制执行此限制是因为WHERE子句是   评估后，列值可能尚未确定。

因此，以下查询是非法的：

SQL> SELECT empno AS employee, deptno AS department, sal AS salary
  2  FROM emp
  3  WHERE employee = 7369;
WHERE employee = 7369
      *
ERROR at line 3:
ORA-00904: "EMPLOYEE": invalid identifier


SQL>

列别名在：

中允许

GROUP BY
ORDER BY
的 HAVING

在以下情况下，您可以参考WHERE子句中的列别名：

的子查询

公用表格表达式（CTE）

例如，

SQL> SELECT * FROM 2 ( 3 SELECT empno AS employee, deptno AS department, sal AS salary 4 FROM emp 5 ) 6 WHERE employee = 7369; EMPLOYEE DEPARTMENT SALARY ---------- ---------- ---------- 7369 20 800 SQL> WITH DATA AS( 2 SELECT empno AS employee, deptno AS department, sal AS salary 3 FROM emp 4 ) 5 SELECT * FROM DATA 6 WHERE employee = 7369; EMPLOYEE DEPARTMENT SALARY ---------- ---------- ---------- 7369 20 800 SQL>

Answer 2

您不能使用在查询

中用作别名的列名

原因：

当时查询将首先检查运行时是否在表“ORDER_ITEMS”中找不到列名“item_total”，因为它是作为别名提供的，它不存储在任何地方，并且您只在所需的输出中分配该列

替代：

如果你想使用那种类型，请使用子查询，它的性能不好但是它是另一种方式

SELECT * FROM
 (SELECT
  ITEM_ID, ITEM_PRICE, DISCOUNT_AMOUNT, QUANTITY, 
  (ITEM_PRICE*QUANTITY) AS price_total, 
  (DISCOUNT_AMOUNT*QUANTITY) AS discount_total, 
  ((ITEM_PRICE-DISCOUNT_AMOUNT)*QUANTITY) AS item_total
 FROM ORDER_ITEMS) as  tbl
WHERE tbl.item_total > 500
ORDER BY tbl.item_total;

Answer 3

从Oracle 12c开始，您可以使用CROSS APPLY定义表达式，然后可以在WHERE子句中引用它们：

SELECT
  o.ITEM_ID, o.ITEM_PRICE, o.DISCOUNT_AMOUNT, o.QUANTITY, 
  s.price_total, s.discount_total, s.item_total
FROM ORDER_ITEMS o
CROSS APPLY (SELECT ITEM_PRICE*QUANTITY AS price_total, 
                    DISCOUNT_AMOUNT*QUANTITY AS discount_total, 
                  (ITEM_PRICE-DISCOUNT_AMOUNT)*QUANTITY AS item_total FROM dual) s
WHERE s.item_total > 500
ORDER BY s.item_total;

SQL无法识别where子句中的列别名

3 个答案: