Enhancement

releated issue: #4609

Test different types to guarantee the correctness of group by:

• decimal32
• int8
• int16
• int32
• int64
• Float32
• Float64
• MyDate
• MyDateTime
• String
• decimal
• enum
• unsigned number

Test group by with different collations:

• ascii_bin
• binary
• gbk_bin
• gbk_chinese_ci
• latin1_bin
• utf8_bin
• utf8_general_ci
• utf8_unicode_ci
• utf8mb4_bin
• utf8mb4_general_ci
• utf8mb4_unicode_ci

Tested aggregation functions:

• max
• min
• count
• sum
• first_row
• group_concat