百度智能云文档 SQL手册 121 2.coalesce 3.if 4.ifnull 5.nullif CASE Description Description 功能：将表达式和多个可能的值进行比较，当匹配时返回相应的结果 返回类型：匹配后返回结果的类型 Example Example Keywords Keywords COALESCE Description Description -------------------------------------------------------------------------------+ case case coalesce coalesce(( expression expression,,value1 value1,,value2…… value2……,,valuen valuen)) Baidu 百度智能云文档 SQL手册 mysql>> select select coalesce coalesce((NULL NULL,, '1111' '1111',, '0000' '0000'));; ++--------------------------------+ --------------------------------+ || coalesce coalesce((NULL NULL,, '1111'