我试图在我的网站上进行有条件的更新。 每当用户单击某个链接时,数据库中的全局计数器变量就会递增。
复杂的是,当计数器数量超过我记录的网站数量时,我希望计数器返回1.我有一个更新声明,但它不起作用,我看不出原因。< / p>
#Increment global counter, set it back to one when it exceeds the number of websites on record
cursor.execute("UPDATE url_reroute_counter SET counter_num = "+
" CASE"+
" WHEN counter_num>(SELECT count(*) FROM url_reroute_targeturl)"+
" THEN counter_num = 1"+
" ELSE"+
" counter_num = counter_num+1"+
" END"+
" WHERE name_of_counter = 'url_count'")`
运行此代码会产生以下异常:
django.db.utils.ProgrammingError: column "counter_num" is of type integer but expression is of type boolean
LINE 1: UPDATE url_reroute_counter SET counter_num = CASE WHEN coun...
^
HINT: You will need to rewrite or cast the expression.
我不习惯在任何SQL语言中使用条件语,因此欢迎任何hlep。
答案 0 :(得分:1)
您的查询应如下
cursor.execute("UPDATE url_reroute_counter SET counter_num = "+
" CASE"+
" WHEN counter_num>(SELECT count(*) FROM url_reroute_targeturl)"+
" THEN 1"+
" ELSE"+
" counter_num+1"+
" END"+
" WHERE name_of_counter = 'url_count'")`
而且顺便说一句,在多行python字符串中,你不需要所有这些+符号。这个:https://stackoverflow.com/a/10660443/267540