Scenes:
Query the same table with different query conditions, but want to combine the query results? Use case when to handle different query conditions.
example:
sql1：
select user_name as username, count(0) as visits from j group by user_name
sql2：
select user_name as username, count(0) as valid times from j where valid='1' group by user_name
At this point, the results of sql1 and sql2 should be merged:
Merge sql:
select user_name as username, count(0) as number of visits, sum(case when valid='1' then 1 else 0 end) as valid number of times from j group by user_name
The above is the use of case when to merge sql, and more usages are welcome to share!
Finally, I wish you all a safe year and no bugs!