mysql - 将重复语句分配给变量

Question

下面是工作存储过程。如何将 case 语句下的重复代码分配给变量并使用它，以便减少编码行数？该过程的目的是使用每个 CASE 语句的 start_date 和 end_date 更新表。感谢您的帮助和建议。

BEGIN
    UPDATE period x
    SET start_date = CASE 
        when return_period = 'L3M' then 
            last_day(date_add((select max(monthend_date) from returns y WHERE x.account_id=y.account_id),INTERVAL -2 Month))
        when return_period = 'YTD' then 
            last_day(date_add((select max(monthend_date) from returns y WHERE x.account_id=y.account_id),INTERVAL 1-MONTH((select max(monthend_date) from returns y 
            WHERE x.account_id=y.account_id)) Month))
        when return_period = '1YR_CUM' or return_period = '1YR_ANN' then             
            last_day(date_add((select max(monthend_date) from returns y WHERE x.account_id=y.account_id),INTERVAL -11 Month))
        when return_period = '2YR_CUM' or return_period = '2YR_ANN' then             
            last_day(date_add((select max(monthend_date) from eturns y WHERE x.account_id=y.account_id),INTERVAL -23 Month))
        when return_period = '3YR_CUM' or return_period = '3YR_ANN' then             
            last_day(date_add((select max(monthend_date) from returns y WHERE x.account_id=y.account_id),INTERVAL -35 Month))
        when return_period = '4YR_CUM' or return_period = '4YR_ANN' then             
            last_day(date_add((select max(monthend_date) from returns y WHERE x.account_id=y.account_id),INTERVAL -47 Month))
        when return_period = '5YR_CUM' or return_period = '5YR_ANN' then             
            last_day(date_add((select max(monthend_date) from returns y WHERE x.account_id=y.account_id),INTERVAL -59 Month))
        when return_period = '6YR_CUM' or return_period = '6YR_ANN' then             
            last_day(date_add((select max(monthend_date) from returns y WHERE x.account_id=y.account_id),INTERVAL -71 Month))
        when return_period = '7YR_CUM' or return_period = '7YR_ANN' then             
            last_day(date_add((select max(monthend_date) from returns y WHERE x.account_id=y.account_id),INTERVAL -83 Month))
        when return_period = '8YR_CUM' or return_period = '8YR_ANN' then             
            last_day(date_add((select max(monthend_date) from returns y WHERE x.account_id=y.account_id),INTERVAL -95 Month))
        when return_period = '9YR_CUM' or return_period = '9YR_ANN' then             
            last_day(date_add((select max(monthend_date) from returns y WHERE x.account_id=y.account_id),INTERVAL -107 Month))
        when return_period = '10YR_CUM' or return_period = '10YR_ANN' then 
            last_day(date_add((select max(monthend_date) from returns y WHERE x.account_id=y.account_id),INTERVAL -119 Month))
        when return_period = '11YR_CUM' or return_period = '11YR_ANN' then 
            last_day(date_add((select max(monthend_date) from returns y WHERE x.account_id=y.account_id),INTERVAL -131 Month))
        when return_period = '12YR_CUM' or return_period = '12YR_ANN' then 
            last_day(date_add((select max(monthend_date) from returns y WHERE x.account_id=y.account_id),INTERVAL -143 Month))
        when return_period = '13YR_CUM' or return_period = '13YR_ANN' then 
            last_day(date_add((select max(monthend_date) from returns y WHERE x.account_id=y.account_id),INTERVAL -155 Month))
        when return_period = '14YR_CUM' or return_period = '14YR_ANN' then 
            last_day(date_add((select max(monthend_date) from returns y WHERE x.account_id=y.account_id),INTERVAL -167 Month))
        when return_period = '15YR_CUM' or return_period = '15YR_ANN' then 
            last_day(date_add((select max(monthend_date) from returns y WHERE x.account_id=y.account_id),INTERVAL -179 Month))
        when return_period = 'SI_CUM' or return_period = 'SI_ANN' then 
            (select min(monthend_date) from returns y WHERE x.account_id=y.account_id)
        END
        ,
        end_date=(select max(monthend_date) from returns y WHERE x.account_id=y.account_id)
        ;
END    

Answer 1

这是您的重复表达式:

last_day(date_add((select max(monthend_date) from returns y WHERE x.account_id=y.account_id),INTERVAL {months} MONTH))

唯一的区别是 {months} 中的值。首先，我将表达式写得短一些:

last_day((select max(monthend_date) from returns y WHERE x.account_id=y.account_id) + INTERVAL {months} MONTH)

然后我将仅对 {month} 部分使用 CASE:

UPDATE period x
SET start_date = last_day((select max(monthend_date) from returns y WHERE x.account_id=y.account_id) + INTERVAL 
        CASE 
            when return_period = 'L3M' then -2
            when return_period = 'YTD' then -1
            when return_period = '1YR_CUM' or return_period = '1YR_ANN' then -11
            when return_period = '2YR_CUM' or return_period = '2YR_ANN' then -23
            when return_period = '3YR_CUM' or return_period = '3YR_ANN' then -35
            when return_period = '4YR_CUM' or return_period = '4YR_ANN' then -47
            # [...]
        END
    MONTH),
    end_date=(select max(monthend_date) from returns y WHERE x.account_id=y.account_id);

你也可以这样写:

UPDATE period x
SET start_date = last_day((select max(monthend_date) from returns y WHERE x.account_id=y.account_id) + INTERVAL 
        CASE return_period
            when 'L3M'     then -2
            when 'YTD'     then -1
            when '1YR_CUM' then -11
            when '1YR_ANN' then -11
            when '2YR_CUM' then -23
            when '2YR_ANN' then -23
            when '3YR_CUM' then -35
            when '3YR_ANN' then -35
            when '4YR_CUM' then -47
            when '4YR_ANN' then -47
            # [...]
        END
    MONTH),
    end_date=(select max(monthend_date) from returns y WHERE x.account_id=y.account_id);