MySQL 'SELECT' 语句中的 'IF' - 根据列值选择输出值
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'IF' in 'SELECT' statement - choose output value based on column values
提问by Michael
SELECT id, amount FROM report
I need amountto be amountif report.type='P'and -amountif report.type='N'. How do I add this to the above query?
我需要的amount是amount，如果report.type='P'和-amount如果report.type='N'。如何将其添加到上述查询中？
回答by Felipe Buccioni
SELECT id,
IF(type = 'P', amount, amount * -1) as amount
FROM report
See http://dev.mysql.com/doc/refman/5.0/en/control-flow-functions.html.
请参阅http://dev.mysql.com/doc/refman/5.0/en/control-flow-functions.html。
Additionally, you could handle when the condition is null. In the case of a null amount:
此外，您可以在条件为空时进行处理。在金额为空的情况下：
SELECT id,
IF(type = 'P', IFNULL(amount,0), IFNULL(amount,0) * -1) as amount
FROM report
The part IFNULL(amount,0)means when amount is not null return amount else return 0.
这部分IFNULL(amount,0)意味着当数量不为空时返回数量否则返回 0。
回答by mellamokb
Use a casestatement:
使用case语句：
select id,
case report.type
when 'P' then amount
when 'N' then -amount
end as amount
from
`report`
回答by user1210826
SELECT CompanyName,
CASE WHEN Country IN ('USA', 'Canada') THEN 'North America'
WHEN Country = 'Brazil' THEN 'South America'
ELSE 'Europe' END AS Continent
FROM Suppliers
ORDER BY CompanyName;
回答by sang kaul
select
id,
case
when report_type = 'P'
then amount
when report_type = 'N'
then -amount
else null
end
from table
回答by aWebDeveloper
Most simplest way is to use a IF(). Yes Mysql allows you to do conditional logic. IF function takes 3 params CONDITION, TRUE OUTCOME, FALSE OUTCOME.
最简单的方法是使用IF()。是的 Mysql 允许你做条件逻辑。IF 函数需要 3 个参数 CONDITION、TRUE OUTCOME、FALSE OUTCOME。
So Logic is
所以逻辑是
if report.type = 'p'
amount = amount
else
amount = -1*amount
SQL
SQL
SELECT
id, IF(report.type = 'P', abs(amount), -1*abs(amount)) as amount
FROM report
You may skip abs() if all no's are +ve only
如果所有的 no 都是 +ve，你可以跳过 abs()
回答by linitux
SELECT id, amount
FROM report
WHERE type='P'
UNION
SELECT id, (amount * -1) AS amount
FROM report
WHERE type = 'N'
ORDER BY id;
回答by Basant Rules
You can try this also
你也可以试试这个
SELECT id , IF(type='p', IFNULL(amount,0), IFNULL(amount,0) * -1) as amount FROM table
