golang查询数据遇到空值问题

Posted 2020-12-01 hxlasky

golang在查询数据库的时候遇到有空值的列,那么后面的字段提取就会失败，针对这种情况可以有2个办法解决:
1.限制数据库不为空或给个默认值，或是在select查询的时候对空值进行处理，使其查出来的数据不为空
2.采用sql.nullstring进行处理

下面的例子就是sql.sqlstring处理:

 

    package main

    import (
        _ "github.com/go-sql-driver/mysql"
        "fmt"
        "database/sql"
    )

    func nulldel(){
        var err error
        connect := "dmladmin:dmladmin@tcp(192.168.1.113:3306)/db_admin"
        db, err := sql.Open("mysql", connect)
        if err != nil{
            fmt.Println("connect mysql failed, address = " + connect, err)
        } else{
            sqlContent := `select
                                t.statedate,
                                t.table_schema,
                                t.table_name,
                  t1.table_comment,
                  t.table_rows,
                                t.lm_table_rows,
                                case when t.lm_table_rows > 0 then
                                round((t.table_rows - t.lm_table_rows)*100/t.lm_table_rows,2)
                                else 0 end growth_rate,
                                t.gather_interval
                            from tb_table_grouth_stat t left join information_schema.tables t1
                            on t.table_schema = t1.table_schema
                     and t.table_name = t1.table_name
                          where t.table_schema not in (‘db_admin‘) and statedate = (select max(statedate) from tb_table_grouth_stat)
         order by 7 desc limit 10`
            rows, err := db.Query(sqlContent)
            if err != nil{
                fmt.Println(err)
            } else{
                for rows.Next() {
                    statedate := sql.NullString{String:"", Valid:false}
                    table_schema := sql.NullString{String:"", Valid:false}
                    table_name := sql.NullString{String:"", Valid:false}
                    table_comment := sql.NullString{String:"", Valid:false}
                    table_rows := sql.NullString{String:"", Valid:false}
                    lm_table_rows := sql.NullString{String:"", Valid:false}
                    growth_rate := sql.NullString{String:"", Valid:false}
                    gather_interval := sql.NullString{String:"", Valid:false}
                    rows.Scan(&statedate, &table_schema, &table_name,&table_comment,&table_rows,&lm_table_rows,&growth_rate,&gather_interval)
                    if ! table_comment.Valid {
                        table_comment.String="未知"
                    }
                    fmt.Println(statedate, table_schema, table_name,table_comment,table_rows,lm_table_rows,growth_rate,gather_interval)
                    fmt.Println(statedate.String, table_schema.String, table_name.String,table_comment.String,table_rows.String,lm_table_rows.String,growth_rate.String,gather_interval.String)
                }
            }
        }
    }
    func main() {
        nulldel()
    }