oracle coalesce函数

在Oracle中，COALESCE函数用于返回参数列表中第一个非NULL的表达式的值。如果所有的表达式都是NULL，则返回NULL值。COALESCE函数的用法为COALESCE(expression_1, expression_2, ..., expression_n)。例如，SELECT COALESCE(NULL, NULL, 3, 4, 5) FROM dual将返回值3，因为3是参数列表中第一个非NULL的值。在COALESCE函数中，所有的表达式必须是相同类型，或者可以隐式转换为相同的类型。使用COALESCE函数可以方便地处理包含空值的表达式，避免计算错误。<span class="em">1</span><span class="em">2</span><span class="em">3</span>
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