针对CASE WHEN函数语句,实现简单CASE函数和CASE搜索函数两种格式。
同时配合 SUM以及COUNT方法的使用
1、CASE 的两种格式: 简单CASE函数和CASE搜索函数
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14**简单CASE函数** CASE 条件参数名称 WHEN 参数值1 THEN '显示值1' WHEN 参数值2 THEN '显示值2' ... ELSE '显示其他值' END **CASE搜索函数** CASE WHEN 条件参数名称 = '参数值1' THEN '显示值1' WHEN 条件参数名称 = '参数值2' THEN '显示值2' ... ELSE '显示其他值' END
两种格式示例:
状态:state
订单号:orderId
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18**简单CASE函数** SELECT orderId, CASE state WHEN 1 THEN '启动' WHEN 2 THEN '关闭' ELSE '未知状态' END AS statusName FROM t_table **CASE搜索函数** SELECT orderId, CASE WHEN state = '1' THEN '启动' WHEN state = '2' THEN '关闭' ELSE '未知状态' END AS stateName FROM t_table
这两种格式式,可以实现相同的功能。但是简单CASE函数和CASE搜索函数相比,功能方面会有些限制,比如写判断式:
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9SELECT orderId, CASE WHEN state = '1' THEN '启动' WHEN state = '2' THEN '关闭' WHEN state IN ('3', '4') THEN '待解锁' ELSE '未知状态' END AS stateName FROM t_table
若是多重时,WHEN 的 IN 条件中的值和下一个 WHEN 的条件重合会被忽略,如下面的 “关闭” 状态会被忽略,永远无法得到 “关闭”
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9SELECT orderId, CASE WHEN state = '1' THEN '启动' WHEN state IN ('2', '3', '4') THEN '待解锁' WHEN state = '2' THEN '关闭' ELSE '未知状态' END AS stateName FROM t_table
2、同时配合 SUM以及COUNT方法的使用
(1)SUM函数
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28**简单CASE函数** SUM(CASE 条件参数名称 WHEN 参数值 THEN '显示被求和值' ELSE 0 END ) AS SUMAMT **CASE搜索函数** SUM(CASE WHEN 条件参数名称 = '参数值' THEN '显示被求和值' ELSE 0 END ) AS SUMAMT **或者** SUM(CASE WHEN 条件参数名称1 = '参数值1' AND 条件参数名称2 = '参数值2' ... THEN '显示被求和值' ELSE 0 END ) AS SUMAMT **或者** SUM(CASE WHEN 条件参数名称1 IN ('参数值n') AND 条件参数名称2 = '参数值2' ... THEN '显示被求和值' ELSE 0 END ) AS SUMAMT
示例: 根据时间条件查询值,有值时显示 “被求和值”, 没有值时,显示 “null”
状态:state
类型:t_type
金额:amt
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52**简单CASE函数** SELECT SUM(CASE state WHEN 1 THEN amt ELSE 0 END ) AS sumAmt FROM t_table WHERE core_time >= '2020-07-01 00:00:00' AND core_time <= '2020-07-20 23:59:59' GROUP BY core_time **CASE搜索函数** SELECT SUM(CASE WHEN state = '1' THEN amt ELSE 0 END ) AS sumAmt FROM t_table WHERE core_time >= '2020-07-01 00:00:00' AND core_time <= '2020-07-20 23:59:59' GROUP BY core_time **或者** SELECT SUM(CASE WHEN state = '1' AND t_type = '2' THEN amt ELSE 0 END ) AS sumAmt FROM t_table WHERE core_time >= '2020-07-01 00:00:00' AND core_time <= '2020-07-20 23:59:59' GROUP BY core_time **或者** SELECT SUM(CASE WHEN state IN ('2', '3', '4') AND t_type = '2' THEN amt ELSE 0 END ) AS sumAmt FROM t_table WHERE core_time >= '2020-07-01 00:00:00' AND core_time <= '2020-07-20 23:59:59' GROUP BY core_time
(2)COUNT函数
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28**简单CASE函数** COUNT(CASE 条件参数名称 WHEN 参数值 THEN 1 ELSE 0 END ) AS COUNTAMT **CASE搜索函数** COUNT(CASE WHEN 条件参数名称 = '参数值' THEN 1 ELSE 0 END ) AS COUNTAMT **或者** COUNT(CASE WHEN 条件参数名称1 = '参数值1' AND 条件参数名称2 = '参数值2' ... THEN 1 ELSE 0 END ) AS COUNTAMT **或者** COUNT(CASE WHEN 条件参数名称1 IN ('参数值n') AND 条件参数名称2 = '参数值2' ... THEN 1 ELSE 0 END ) AS COUNTAMT
示例: 根据时间条件查询值,有值时显示 “总条数值”, 没有值时,显示 “0”
状态:state
类型:t_type
金额:amt
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52**简单CASE函数** SELECT COUNT(CASE state WHEN 1 THEN 1 ELSE 0 END ) AS countAmt FROM t_table WHERE core_time >= '2020-07-01 00:00:00' AND core_time <= '2020-07-20 23:59:59' GROUP BY core_time **CASE搜索函数** SELECT COUNT(CASE WHEN state = '1' THEN 1 ELSE 0 END ) AS countAmt FROM t_table WHERE core_time >= '2020-07-01 00:00:00' AND core_time <= '2020-07-20 23:59:59' GROUP BY core_time **或者** SELECT COUNT(CASE WHEN state = '1' AND t_type = '2' THEN 1 ELSE 0 END ) AS countAmt FROM t_table WHERE core_time >= '2020-07-01 00:00:00' AND core_time <= '2020-07-20 23:59:59' GROUP BY core_time **或者** SELECT COUNT(CASE WHEN state IN ('2', '3', '4') AND t_type = '2' THEN 1 ELSE 0 END ) AS countAmt FROM t_table WHERE core_time >= '2020-07-01 00:00:00' AND core_time <= '2020-07-20 23:59:59' GROUP BY core_time
最后
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