[英]How to simplify SQL Code with IF condition. (Postgresql)
I want to simplify the below sql code without change the business logic.here I mentioned postgresql code that I want to modify. 我想简化下面的sql代码而不改变业务逻辑。我提到了我想要修改的postgresql代码。
SELECT IF(
(SELECT `rate` FROM `vat_rate` WHERE '2017-05-12' BETWEEN from_date AND to_date) is not null ,
(SELECT `rate` FROM `vat_rate` WHERE '2017-05-12' BETWEEN from_date AND to_date) ,
IF((SELECT `rate` FROM `vat_rate` WHERE from_date is null and '2017-05-12' < to_date ) is not null,
(SELECT `rate` FROM `vat_rate` WHERE from_date is null and '2017-05-12' < to_date ),
IF(
(SELECT `rate` FROM `vat_rate` WHERE to_date is null and '2017-05-12' > from_date) is not null,
(SELECT `rate` FROM `vat_rate` WHERE to_date is null and '2017-05-12' > from_date),
'not found'
)
)
) as rate
The complexity is caused by allowing NULLs in the dates. 复杂性是由允许日期中的NULL引起的。 Using
-infinity
and (+) infinity
as the default values would have avoided the tests for NULL dates. 使用
-infinity
和(+) infinity
作为默认值可以避免测试NULL日期。 Changing the table definition: 更改表定义:
ALTER TABLE vat_rate
ALTER COLUMN from_date SET DEFAULT '-infinity'
, ALTER COLUMN to_date SET DEFAULT 'infinity'
;
UPDATE vat_rate SET from_date = DEFAULT WHERE from_date IS NULL;
UPDATE vat_rate SET to_date = DEFAULT WHERE to_date IS NULL;
ALTER TABLE vat_rate
ALTER COLUMN from_date SET NOT NULL
, ALTER COLUMN to_date SET NOT NULL
;
could reduce your query to just: 可以将您的查询减少到:
SELECT rate AS the_reet
FROM vat_rate
WHERE '2017-05-12' BETWEEN from_date AND to_date
;
If you cannot change the table definition, you could fold the date values inside the query: 如果无法更改表定义,则可以在查询中折叠日期值:
SELECT rate AS the_reet
FROM vat_rate
WHERE '2017-05-12' BETWEEN COALESCE(from_date, '-infinity'::date)
AND COALESCE(to_date, 'infinity'::date)
;
Avoiding the COALESCE() (this could be faster) 避免COALESCE()(这可能会更快)
SELECT rate AS the_reet
FROM vat_rate
WHERE ('2017-05-12' >= from_date OR from_date IS NULL)
AND ( '2017-05-12' <= to_date OR to_date IS NULL)
;
The extreme case of no matching range could be solved by adding a union. 可以通过添加联合来解决没有匹配范围的极端情况。
You're after the Coalesce()
operator: 你在
Coalesce()
运算符之后:
SELECT
COALESCE (
(SELECT rate FROM vat_rate WHERE '2017-05-12' BETWEEN from_date AND to_date),
(SELECT rate FROM vat_rate WHERE from_date is null and '2017-05-12' < to_date ),
(SELECT rate FROM vat_rate WHERE to_date is null and '2017-05-12' > from_date),
'not found'
) as rate
Why not just use CASE EXPRESSION
directly on the vat_rate
table instead of selecting each value from it over and over? 为什么不直接在
vat_rate
表上使用CASE EXPRESSION
而不是vat_rate
选择每个值? Here is a solution that should do the same using conditional aggregation : 这是一个使用条件聚合应该做同样的解决方案:
SELECT COALESCE(t.val_1,t.val_2,t.val_3) as calc_col
FROM (
SELECT MAX(CASE WHEN vat_rate between from_date AND to_date THEN rate END) as val_1,
MAX(CASE WHEN from_date is null and '2017-05-12' < to_date THEN rate END) as val_2,
MAX(CASE WHEN to_date is null and '2017-05-12' > from_date THEN rate END) as val_3
FROM vat_rate) t
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