[Bug] Fix analysis error when there are different types in case-when-then-else with group by clause

[xy720]

Proposed changes

Fix #4645

Relevant pr #3396

To Reproduce
Steps to reproduce the behavior:

1. create table

+----------------------+-------------+------+-------+---------------------+---------+
| Field                | Type        | Null | Key   | Default             | Extra   |
+----------------------+-------------+------+-------+---------------------+---------+
| event_day            | INT         | No   | true  | NULL                |         |
| event_hour           | TINYINT     | No   | true  | 0                   |         |
| event_minute         | TINYINT     | No   | true  | 0                   |         |
| event_time           | DATETIME    | No   | true  | 1970-01-01 00:00:00 |         |
| search_page          | VARCHAR(30) | No   | true  |                     |         |
| search_source        | TINYINT     | No   | true  | 0                   |         |
| soft_version         | VARCHAR(30) | No   | true  |                     |         |
| not_arrived_category | VARCHAR(30) | No   | true  |                     |         |
| pv                   | FLOAT       | No   | false | 0                   | REPLACE |
+----------------------+-------------+------+-------+---------------------+---------+

CREATE TABLE `test_tbl` (
  `event_day` int(11) NOT NULL COMMENT "日期,如20191016",
  `event_hour` tinyint(4) NOT NULL DEFAULT "0" COMMENT "小时,如8",
  `event_minute` tinyint(4) NOT NULL DEFAULT "0" COMMENT "分钟,如59",
  `event_time` datetime NOT NULL DEFAULT "1970-01-01 00:00:00" COMMENT "隶属时间(区间查询用)",
  `search_page` varchar(30) NOT NULL DEFAULT "" COMMENT "page来源",
  `search_source` tinyint(4) NOT NULL DEFAULT "0" COMMENT "search_source来源",
  `soft_version` varchar(30) NOT NULL DEFAULT "" COMMENT "APP版本,如11.15.0.2",
  `not_arrived_category` varchar(30) NOT NULL DEFAULT "" COMMENT "未到达原因",
  `pv` float NOT NULL DEFAULT "0" COMMENT "聚合pv数"
) ENGINE=OLAP
UNIQUE KEY(`event_day`, `event_hour`, `event_minute`, `event_time`, `search_page`, `search_source`, `soft_version`, `not_arrived_category`)
COMMENT "OLAP"
PARTITION BY RANGE(`event_day`)
(PARTITION p202006 VALUES [("20200601"), ("20200701")),
PARTITION p202007 VALUES [("20200701"), ("20200801")),
PARTITION p202008 VALUES [("20200801"), ("20200901")),
PARTITION p202009 VALUES [("20200901"), ("20201001")),
PARTITION p202010 VALUES [("20201001"), ("20201101")),
PARTITION p202011 VALUES [("20201101"), ("20201201")),
PARTITION p202012 VALUES [("20201201"), ("20210101")))
DISTRIBUTED BY HASH(`event_day`) BUCKETS 16
PROPERTIES (
"replication_num" = "3",
"in_memory" = "false",
"storage_format" = "V2"
);

2. input sql

    SELECT
        case when "condition" = ' ' then 'string' else search_source end as search_source
    FROM test_tbl
    GROUP BY search_source

3. doris report an analysis error.

In the sql above, search_source is a TINYINT type and 'string' is VARCHAR(*) type. Because the value of WhenExpr "condition" = ' ' is false, so this case-when clause will produce a CastExpr as SelectListItem with a TINYINT type SlotRef child represents search_source after rewriting the sql. However, the analyzeAggregation() method cannot handle the case where SelectListItem is CaseExpr(implicitCast).

Expected behavior
Analysis successfully.

Types of changes

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• Bugfix (non-breaking change which fixes an issue)

Checklist

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• I have create an issue on (Fix [Bug] An analysis error will report when there are different types in case-when-then-else with group by clause #4645 ), and have described the bug/feature there in detail
• Compiling and unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works

Further comments

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[morningman]

LGTM