Dynamic Pivot CASE WHEN 出现错误 #1064 - 你的 SQL 语法有错误；答案

【问题标题】：Dynamic Pivot CASE WHEN got error #1064 - You have an error in your SQL syntax;Dynamic Pivot CASE WHEN 出现错误 #1064 - 你的 SQL 语法有错误；
【发布时间】：2023-02-23 16:32:05
【问题描述】：

SET @sql = NULL;
set @sql = (
                select group_concat(distinct
                concat(
                "(CASE WHEN param_code IN ('20', '43')
                THEN EXP(AVG(CASE WHEN YEAR(`res_date`) = '", YEAR(`res_date`),"'  THEN LOG(`res_value`) END))
                ELSE AVG(CASE WHEN YEAR(`res_date`) =  '", YEAR(`res_date`),"'  THEN `res_value` END)
                END) as  '",YEAR(`res_date`),"'"
                )   
                )
                from wq_results
                );
                
set @sql = concat("select station_id AS ID, tbl2.station_name, param_code, ", @sql, " from wq_results as tbl1 left join mon_stations as tbl2 on tbl1.station_id = tbl2.id  where sc_id='20' and param_code = IN (20,43) group by station_id");
prepare stmt from @sql;
execute stmt;

tbl1 wq_results

id	station_id	param_code	res_value	res_date
1	1	20	1,452	2021-12-06
2	1	20	85	2022-12-06
3	1	20	1,854	2023-01-06
4	1	43	67	2023-01-06
5	2	43	1,285	2023-12-06

tbl2 mon_stations

id	station_name
1	Station 1
2	Station 2

输出应该是这样的

Station ID	Station Name	Parameter	2021	2022	2023
1	Station 1	20	1,452	85	8,254
2	Station 2	43	-	-	1,285
1	Station 1	43	-	-	67

【问题讨论】：

其中 sc_id='20' 和 param_code = IN (20,43) - remove = voting to close as typo 另外 sc_id 从哪里来？

标签： mysql

【解决方案1】：

尝试这个：

你有一个与group by相关的错误，你应该包括tbl1.station_id, tbl2.station_name, param_code

可以删除 where 子句

SET @sql = NULL;
set @sql = (
            select group_concat(
                  distinct concat(
                "(CASE WHEN param_code IN ('20', '43') THEN EXP(AVG(CASE WHEN YEAR(`res_date`) = '", YEAR(`res_date`),"'  THEN LOG(`res_value`) END)) ELSE AVG(CASE WHEN YEAR(`res_date`) =  '", YEAR(`res_date`),"'  THEN `res_value` END) END) 
                 as  '",YEAR(`res_date`), "'"
                  )   
            )
            from wq_results
          );
                
set @sql = concat("select tbl1.station_id AS ID, tbl2.station_name, param_code, ", @sql, " 
                 from wq_results as tbl1 
                 left join mon_stations as tbl2 on tbl1.station_id = tbl2.id  
                 where param_code IN (20,43) 
                 group by tbl1.station_id, tbl2.station_name, param_code");
select @sql;
prepare stmt from @sql;
execute stmt;

Demo here

【讨论】：