改进代码if startT == "" || endT == "" { sqlstr = "" } else { var buf bytes.Buffer fmt.Fprintf(&buf, "AND created_at BETWEEN %s AND %s", startT, endT) sqlstr = buf.String() } res := common.DB.Raw("SELECT * FROM(SELECT id,created_at,type,source,explanation,label,location,facility_id,pm_id FROM flaws WHERE facility_id = ? "+sqlstr, "UNION SELECT id,created_at,type,source,explanation,label,location,facility_id,pm_id FROM issues WHERE facility_id = ? "+sqlstr, "UNION SELECT id,created_at,type,source,explanation,label,location,facility_id,pm_id FROM records WHERE facility_id = ? "+sqlstr, "UNION SELECT id,created_at,type,source,explanation,label,location,facility_id,pm_id FROM qualities WHERE facility_id = ? "+sqlstr, "UNION SELECT id,created_at,type,source,explanation,label,location,facility_id,pm_id FROM inspections WHERE facility_id = ?)"+sqlstr, "AS combined_tables LIMIT ? OFFSET ?", code, code, code, code, code, pageSize, offset).Find(&req)

这段代码已经比较简洁和清晰，但还可以做一些改进。下面是一些可能的改进方向：

1. 使用预处理语句避免 SQL 注入漏洞。在 Go 语言中，可以使用 database/sql 包中的 Prepare 和 Exec 函数来执行预处理语句，这样可以避免 SQL 注入漏洞。

2. 使用常量或变量来存储查询语句的模板，避免在代码中硬编码 SQL 查询语句。这样可以提高代码的可读性和可维护性。

3. 将查询语句和查询参数分开处理，避免将查询参数直接拼接到查询语句中，提高代码的可读性和可维护性。

4. 对于大型的 SQL 查询语句，可以使用多行字符串来存储查询语句，提高代码的可读性。例如：

sql := `SELECT *
        FROM table1
        JOIN table2 ON table2.id = table1.table2_id
        WHERE table1.id = ?`

5. 使用结构体来存储查询参数，提高代码的可读性和可维护性。例如：

type QueryParams struct {
    Code    string
    StartT  string
    EndT    string
    PageSize int
    Offset  int
}

func GetQueryResults(params QueryParams) ([]Record, error) {
    // ...
}