SQL 无法识别 where 子句中的列别名

Question

我只是 SQL 的初学者，但我遇到了这个烦人的错误。 SQL 此脚本的 WHERE 子句有问题：

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;

我收到这个错误：

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 price_total 和 discount_total 都没有问题，但报告 item_total 无效。我试图首先 select 仅减去折扣金额并乘以数量时总计大于 500 的项目。然后，我需要按 item_total

降序排列结果

Answer 1

An alias can be used in a query select list to give a column a different name. You can use the alias in GROUP BY, ORDER BY, or HAVING clauses to refer to the column.

Standard SQL disallows references to column aliases in a WHERE clause. This restriction is imposed because when the WHERE clause is evaluated, the column value may not yet have been determined.

所以，下面的查询是非法的：

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>

允许使用列别名：

分组依据
订购方式
有

以下情况可以在WHERE子句中引用列别名：

子查询
普通Table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：

查询将首先检查运行时列名 "item_total" 在 table "ORDER_ITEMS" 中找不到，因为它是作为别名提供的，没有存储在任何地方并且您仅在所需输出中分配该列

备用：

如果您想使用该类型与子查询一起使用，它的性能并不好，但它是替代方法之一

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，然后您可以在 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

SQL not recognizing column alias in where clause

sql

oracle

column-alias