GORM docs: https://gorm.io/docs/sql_builder.html

Pattern: Build SQL fragments + struct holding all possible parameters. Use @FieldName placeholders—GORM matches exported struct fields.

type MerchBill struct {
    ID        uint           `gorm:"primarykey"`
    CreatedAt time.Time
    UpdatedAt time.Time
    DeletedAt gorm.DeletedAt `gorm:"index" json:"-"`
    Applyno   string         `gorm:"column:applyno;type:varchar(255);comment:订单号;"`
}

func getList(info req.Mer) (err error, list interface{}, total int64) {
    db := DB.Model(&MerchBill{}) // assume DB is *gorm.DB

    var bills []MerchBill
    var countWrap []struct{ Countnum int64 }

    baseSelect := "SELECT bill.*, mer.mobile, mer.merchname"
    baseCount  := "SELECT COUNT(*) AS countnum"
    whereSql   := " FROM billtable AS bill LEFT JOIN merch_user AS mer ON mer.id = bill.merchid WHERE 1"

    var param struct {
        Applyno       string
        Status        *int
        Applytype     *int
        Applyrealname string
        Merchname     string
        Limit         int
        Offset        int
    }

    if info.Applyno != "" {
        whereSql += " AND bill.applyno = @Applyno"
        param.Applyno = info.Applyno
    }
    if info.Status != nil {
        whereSql += " AND bill.status = @Status"
        param.Status = info.Status
    }
    if info.Applytype != nil {
        whereSql += " AND bill.applytype = @Applytype"
        param.Applytype = info.Applytype
    }
    if info.Applyrealname != "" {
        whereSql += " AND bill.applyrealname = @Applyrealname"
        param.Applyrealname = info.Applyrealname
    }
    if info.Merchname != "" {
        whereSql += " AND mer.merchname LIKE @Merchname"
        param.Merchname = info.Merchname
    }

    orderLimit := " ORDER BY bill.id DESC LIMIT @Offset,@Limit"
    param.Limit = info.PageSize
    param.Offset = info.PageSize * (info.Page - 1)

    if err = db.Raw(baseSelect+whereSql+orderLimit, param).Scan(&bills).Error; err != nil { return }
    if err = db.Raw(baseCount+whereSql, param).Scan(&countWrap).Error; err != nil { return }
    total = countWrap[0].Countnum
    return err, bills, total
}

Tips:

  1. Always export struct fields (capitalized) for binding.
  2. Keep one param struct—unused fields are ignored.
  3. Use IN (@Param) style only with slices supported; for complex dynamic lists, build placeholders explicitly.