SQL Oracle 中的 if(condition, then, else)
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if(condition, then, else) in Oracle
提问by ModeEngage
MySQL/MSSQL has a neat little inline if function you can use within queries to detect null values, as shown below.
MySQL/MSSQL 有一个简洁的内联 if 函数，您可以在查询中使用它来检测空值，如下所示。
SELECT
...
foo.a_field AS "a_field",
SELECT if(foo.bar is null, 0, foo.bar) AS "bar",
foo.a_field AS "a_field",
...
The problem I'm running into now is that this code is not safe to run on an Oracle database, as it seems not to support this inline if syntax.
我现在遇到的问题是这段代码在 Oracle 数据库上运行不安全，因为它似乎不支持这种内联 if 语法。
Is there an equivalent in Oracle?
Oracle 中是否有等价物？
回答by David Andres
To supplement the rest of the answers here, which deal primarily with NULL values and COALESCE/NVL/NVL2:
补充此处的其余答案，主要处理 NULL 值和 COALESCE/NVL/NVL2：
SELECT *
FROM TheTable
WHERE field1 = CASE field2 WHEN 0 THEN 'abc' WHEN 1 THEN 'def' ELSE '' END
CASE statements are not as succinct, obviously, but they are geared towards flexibility. This is particularly useful when your conditions are not based on NULL-ness.
显然，CASE 语句没有那么简洁，但它们是面向灵活性的。当您的条件不基于 NULL 性时，这特别有用。
回答by Tony Andrews
Use the standard COALESCE function:
使用标准 COALESCE 函数：
SELECT COALESCE(foo.bar, 0) as "bar", ...
Or use Oracle's own NVL function that does the same.
或者使用 Oracle 自己的 NVL 函数来做同样的事情。
回答by OMG Ponies
回答by SquareCog
You want the nvl function: nvl(foo.bar, 0)
你想要 nvl 函数： nvl(foo.bar, 0)
Oracle does support various ifs and cases as well.
Oracle 也支持各种 if 和 case。
回答by tuinstoel
Just do nvl(foo.bar,0), you don't have to do
做nvl(foo.bar,0)，你不必做
(select nvl(foo.bar,0)...
