oracle case when 字段比较

在Oracle中，可以使用CASE WHEN语句来比较字段的值。在使用CASE WHEN语句时，可以根据需要进行等值判断或表达式判断。与DECODE函数相比，CASE WHEN更灵活，可以用于=，>=，<，<=，<>，IS NULL，IS NOT NULL，BETWEEN等多种判断条件。以下是一些示例：

1. 使用CASE WHEN进行等值判断：

SELECT CASE WHEN 字段名 = '1' THEN '条件1' 
            WHEN 字段名 = '2' THEN '条件2' 
            ELSE '其他条件' 
       END AS 别名
FROM 表名;

2. 使用CASE WHEN进行表达式判断：

SELECT CASE WHEN INSTR(hiredate, '82') = 0 THEN 0 
            ELSE 1 
       END AS "year"
FROM emp;

3. 使用CASE WHEN进行多条件判断和求和：

SELECT COUNT(*) AS total,
       SUM(CASE WHEN INSTR(hiredate, '80') = 0 THEN 0 
                ELSE 1 
           END) AS "1980",
       SUM(CASE WHEN INSTR(hiredate, '81') = 0 THEN 0 
                ELSE 1 
           END) AS "1981",
       SUM(CASE WHEN INSTR(hiredate, '82') = 0 THEN 0 
                ELSE 1 
           END) AS "1982",
       SUM(CASE WHEN INSTR(hiredate, '87') = 0 THEN 0 
                ELSE 1 
           END) AS "1987"
FROM emp;

以上是使用CASE WHEN对字段进行比较的示例。可以根据实际需求灵活运用CASE WHEN来满足不同的条件判断和逻辑运算。<span class="em">1</span><span class="em">2</span><span class="em">3</span>
#### 引用[.reference_title]
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