使用单个 SQL 查询计算列中给定值列表的出现次数

Question

I would like to get the count of occurrences of a given list of values in a column using a single SQL query. The operations must be optimised for performance.

Please refer the example given below,

Sample Table name - history

code_list
5lysgj
627czl
1lqnd8
627czl
dtrtvp
627czl
esdop9
esdop9
3by104
1lqnd8

Expected Output

Need to get the count of occurrences for these given list of codes 627czl, 1lqnd8, esdop9, aol4m6 in the format given below.

code	count
627czl	3
esdop9	2
1lqnd8	2
aol4m6	0

Method I tried in show below but the count of each input is shown as a new column using this query,

SELECT 
    sum(case when h.code_list = 'esdop9' then 1 else 0 end) AS count_esdop9,
    sum(case when h.code_list = '627czl' then 1 else 0 end) AS count_627czl,
    sum(case when h.code_list = '1lqnd8' then 1 else 0 end) AS count_1lqnd8,
    sum(case when h.code_list = 'aol4m6' then 1 else 0 end) AS count_aol4m6
FROM history h;

Note - The number inputs need to be given in the query in 10 also the real table has millions of records.

Answer 1

If i properly understand you need to get the count of occurrences for the following codes: 627czl , 1lqnd8 , esdop9 .

In this case you can try this one:

SELECT code_list, count(*) as count_
  FROM history
 WHERE code_list in ('627czl','1lqnd8','esdop9')
 GROUP BY code_list
 ORDER BY count_ DESC;

dbfiddle

If you need to get the count of occurrences for all codes you can run the following query:

SELECT code_list, count(*) as count_
  FROM history
 GROUP BY code_list
 ORDER BY count_ DESC;

Answer 2

you can try to use GROUP BY Something like this

SELECT code_list, COUNT(1) as 'total' ROM h GROUP by code_list order by 'total' ;