What are the problems with SQL's use of if in business
What is the problem of SQL using if in business? many novices are not very clear about it. In order to help you solve this problem, the following editor will explain it in detail. People with this need can come and learn. I hope you can get something.
If (true,'1','0')
If is an either-or choice in sql, so you need to pay attention to business issues when using it:
For example:
Determine whether a user is newly registered or an old registered user
Select
Tb.*
, if (t_user.user_id is not null,' newly registered user', 'old registered user') as new_sign_user
From tb
Left join t_user # # user id is unique
On tb.ds = t_user.ds
And tb.user_id = t_user.user_id
There is no problem in registering new and old users, because users have only two attributes, either new registration or old registration, and there is no problem with using if
Problem: judging the select of new paying users
Tb.*
, case when t_first_pay.from_user_id is not null and t_first_pay.ds < tb.ds then 'old payment'
When t_first_pay.from_user_id is not null and t_first_pay.ds = tb.ds then 'new payment'
Else 'unpaid' end as new_pay_user
From tb
Left join t_trade_flow_first_type as t_first_pay # # first payment by users
On tb.ds = t_first_pay.ds
And tb.user_id = t_first_pay.user_id
Paying users have three attributes: old payment attribute, new payment attribute and non-payment attribute, so if decision can no longer be used. Multiple decisions need to be made using case when.
If works best, but you also need to pay attention to business scenarios and exhaust business possibilities.
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