sql - DB2 AS/400 系列 在 where 子句中使用别名

Question

我正在尝试在 where 子句中使用列的别名。例如：

SELECT col1 AS alias1, col2 + col3 as sums 
FROM my_table
WHERE sums > 10

但后来我收到一条错误消息：

列总和不在指定表中。

无论如何我可以做到这一点吗？

Answer 1

如果您真的想在中使用别名WHERE，而不是列本身，则可以使用派生表：

SELECT a.* 
FROM
(
  SELECT lmITNO AS Item_Number, lmBANO AS Lot, lmSTAS AS Status, 
  lmRORN AS Order_Number 
  FROM MVXJDTA.MILOMA 
) a
WHERE a.Status = 'CCC'
....

Answer 2

The where-clause is processed before the select-clause in a statement:

The WHERE clause specifies an intermediate result table that consists of those rows of R for which the search-condition is true. R is the result of the FROM clause of the statement.

Re-write the where-clause to reference the actual column name:

...
WHERE A.lmSTAS = 'CCC'
...

A common-table-expression can be used to pre-process the select-clause. For example:

WITH A AS (SELECT 
    lmITNO AS Item_Number, 
    lmBANO AS Lot, 
    lmSTAS AS Status, 
    lmRORN AS Order_Number 
FROM MVXJDTA.MILOMA)
SELECT A.* FROM A WHERE A.Status = 'CCC'
FETCH FIRST 1000 ROWS ONLY

The columns in a CTE can also be renamed by listing them after the table-identifier. For example:

WITH A (Item_Number, Lot, Status, Order_Number)
AS (SELECT 
    lmITNO, 
    lmBANO, 
    lmSTAS, 
    lmRORN
FROM MVXJDTA.MILOMA)
SELECT A.* FROM A WHERE A.Status = 'CCC'
FETCH FIRST 1000 ROWS ONLY