1. 实现配置文件解析

2. 实现数据库连接

vendor/gorm.io/gorm/clause/group_by.go

@@ -0,0 +1,48 @@
+package clause
+
+// GroupBy group by clause
+type GroupBy struct {
+	Columns []Column
+	Having  []Expression
+}
+
+// Name from clause name
+func (groupBy GroupBy) Name() string {
+	return "GROUP BY"
+}
+
+// Build build group by clause
+func (groupBy GroupBy) Build(builder Builder) {
+	for idx, column := range groupBy.Columns {
+		if idx > 0 {
+			builder.WriteByte(',')
+		}
+
+		builder.WriteQuoted(column)
+	}
+
+	if len(groupBy.Having) > 0 {
+		builder.WriteString(" HAVING ")
+		Where{Exprs: groupBy.Having}.Build(builder)
+	}
+}
+
+// MergeClause merge group by clause
+func (groupBy GroupBy) MergeClause(clause *Clause) {
+	if v, ok := clause.Expression.(GroupBy); ok {
+		copiedColumns := make([]Column, len(v.Columns))
+		copy(copiedColumns, v.Columns)
+		groupBy.Columns = append(copiedColumns, groupBy.Columns...)
+
+		copiedHaving := make([]Expression, len(v.Having))
+		copy(copiedHaving, v.Having)
+		groupBy.Having = append(copiedHaving, groupBy.Having...)
+	}
+	clause.Expression = groupBy
+
+	if len(groupBy.Columns) == 0 {
+		clause.Name = ""
+	} else {
+		clause.Name = groupBy.Name()
+	}
+}