Go language error handling for MySQL data query

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Go language error handling for MySQL data query package mainimport ("Database/sql" "FMT" "Runtime")//Go Run Test.gofunc Main () {// MySQL extension https://github.com/go-sql-driver/mysql db, err: = SQL. Open ("MySQL", "Root: @tcp (127.0.0.1:3306)/test?charset=utf8") if err! = Nil {fmt. PRINTLN (ERR)}//DB connection generally does not shut down actively, unless it is confirmed that the connection is no longer needed, go will recycle defer db.        Close ()//user model, table structure, requires a structure to receive the query result set type User struct {Id int32 Name string Age int8} Save user Information list var user user//1, query a series of values//query result set needs to call the next () method to go through rows, err: = db. Query (' SELECT id,name,age from user ') if err! = Nil {fmt. PRINTLN (ERR)} defer rows. Close () for rows. Next () {//For traversal, it is only necessary to determine if there is an error each time//parameter binding requires number and position one by one corresponds to If err: = rows. Scan (&user. Id, &user. Name, &user. Age); Err! = Nil {fmt. PRINTLN (ERR) continue} FMT. Println (user. Id, user. Name, user. Age)}//After processing is complete, you need to determine the traversalIf there is an error in the procedure to produce if err: = rows. ERR (); Err! = Nil {fmt. PRINTLN (ERR)}//2, query a record//query a record, cannot use similar if err: = db. Queryrow (). Scan (& ...); Err! = Nil {} is processed//because when querying a single data, var errnorows = errors may be returned. New ("Sql:no rows in result set") This type of error message//And this is a normal error, err = db.    Queryrow (' SELECT id,name,age WHERE id =? ', 2). Scan (&user. Id, &user. Name, &user. Age,) switch {case err = = SQL. Errnorows:case Err! = Nil://Use this method to print out the runtime error message, which is not determined at compile time if _, file, line, OK: = runtime. Caller (0); OK {fmt. PRINTLN (err, file, line)}} FMT. Println (user. Id, user. Name, user. Age)//3, about null//All fields queried are not allowed to have null, the best way to avoid this is to create a table field, do not set similar to the default NULL property//There are some unavoidable situations, such as the following query/ /The query, if it does not exist, returns a value of NULL instead of 0, for that simple query, directly using the HAVING clause can//specific query, need in the process of encoding self-processing var age int32 err = db.        Queryrow (' SELECT SUM (age) ' age from user WHERE id =? Having aGE <> NULL ', 10). Scan (&age) Switch {case err = = SQL. Errnorows:case Err! = nil:fmt. PRINTLN (Err)} FMT. Println (age)}