生成_series 的 Postgres 查询中的占位符返回未知

Question

我尝试使用这样的占位符进行查询

database.Query("select login,displayname from (select distinct $1+trunc(random()*$2)::integer as id from generate_series($3,$4) g ) r join users using(id) limit 10",min_id,max_id-min_id,min_id,max_id)

它给我一个错误：

pq: function generate_series(unknown, unknown) is not unique

然后我找到了一个将查询格式化为字符串的解决方案

query:=fmt.Sprintf("select login,displayname from (select distinct %v+trunc(random()*%v)::integer as id from generate_series(%v,%v) g ) r join users using(id) limit 10",min_id,max_id-min_id,min_id,max_id)

它有效。

我想让它以正确的方式工作，但我不明白为什么不这样做。

更新：

var min_id int64

var max_id int64

err:=_database.QueryRow("select min(id),max(id) from users").Scan(&min_id, &max_id)

if err!=nil { 

    log.Panicf("Failed to get min and max %v",err.Error())

    return

}

var rows *sql.Rows

query:=fmt.Sprintf("select login,displayname from (select distinct %v+trunc(random()*%v)::integer as id from generate_series(%v,%v) g ) r join users using(id) limit 10",min_id,max_id-min_id,min_id,max_id)

log.Printf(query)

rows,err=_database.Query("select login,displayname from (select distinct $1+trunc(random()*$2)::integer as id from generate_series($3,$4) g ) r join users using(id) limit 10",min_id,max_id-min_id,min_id,max_id)

if err!=nil {

    log.Panicf("failed to get random entries: %v",err)

}

Answer 1

尝试拆分您的查询。你会看到第一部分工作正常：db.QueryRow("SELECT $1+trunc(random()*$2) as test", 10, 5)这可能是因为$1和$2与数学运算符一起使用（和/或因为trunc()和random()两者都返回数字），所以 postgres 可以推断数据类型。所以看起来是generate_series()参数没有被正确确定。Postgres可以根据参数推断数据类型，例如if err := db.QueryRow("SELECT trunc($1,2) as test", 1.4343).Scan(&output); err != nil {panic(err)}// output = 1.43但是，如果它是一个多态函数，歧义就会出现并且会失败，例如if err := db.QueryRow("SELECT trunc($1) as test", 1.4343).Scan(&output); err != nil {panic(err)}// panic: pq: function trunc(unknown) is not unique为避免歧义，请在准备好的语句中显式转换参数，例如： generate_series($3::int,$4::int)