mysql: *sql.DB invalid memory address or nil pointer dereference

@methane, you were right, I had to change db, err := [...] with db, err = [...] declaring also error. My bad, distraction error.

db, err := sql.Open("mysql", "<USERNAME>:<PASSWORD>@tcp(<HOST>:3306)/<DB_NAME>")

Then, db is local variable of main, not global variable _getJSON() using.

Without you provide complete reproducible code, no one can point out where your code have race condition. go build -race is your friend.

@DaniloPolani Your db is nil.

I’m having too this problem, go version is go1.7.4 linux/amd64 and go-sql-driver is the latest. I’m connecting to a RDS instance of AWS.

runtime error: invalid memory address or nil pointer dereference
/usr/local/go/src/runtime/panic.go:458 (0x42c653)
	gopanic: reflectcall(nil, unsafe.Pointer(d.fn), deferArgs(d), uint32(d.siz), uint32(d.siz))
/usr/local/go/src/runtime/panic.go:62 (0x42b1ad)
	panicmem: panic(memoryError)
/usr/local/go/src/runtime/sigpanic_unix.go:24 (0x441054)
	sigpanic: panicmem()
/usr/local/go/src/database/sql/sql.go:781 (0x557d0a)
	(*DB).conn: db.mu.Lock()
/usr/local/go/src/database/sql/sql.go:1074 (0x559fbb)
	(*DB).query: ci, err := db.conn(strategy)
/usr/local/go/src/database/sql/sql.go:1062 (0x559dc0)
	(*DB).Query: rows, err = db.query(query, args, cachedOrNewConn)
/home/danilo/Go/src/github.com/DaniloMeritocracy/autocomplete/autocomplete.go:192 (0x402e27)
	_getJSON: rows, err := db.Query(sqlString)
/home/danilo/Go/src/github.com/DaniloMeritocracy/autocomplete/autocomplete.go:130 (0x402b54)
	school: res, err := _getJSON("SELECT * FROM university WHERE LOWER(name) LIKE '" + strings.Replace(term, "'", "\\'", -1) + "%' LIMIT 15")
/home/danilo/Go/src/github.com/DaniloMeritocracy/autocomplete/autocomplete.go:56 (0x403985)
	main.func1: results = school(term)
/home/danilo/Go/src/gopkg.in/gin-gonic/gin.v1/context.go:97 (0x45d53a)
	(*Context).Next: c.handlers[c.index](c)
/home/danilo/Go/src/gopkg.in/gin-gonic/gin.v1/recovery.go:45 (0x46d31a)
	RecoveryWithWriter.func1: c.Next()
/home/danilo/Go/src/gopkg.in/gin-gonic/gin.v1/context.go:97 (0x45d53a)
	(*Context).Next: c.handlers[c.index](c)
/home/danilo/Go/src/gopkg.in/gin-gonic/gin.v1/logger.go:72 (0x46c40f)
	LoggerWithWriter.func1: c.Next()
/home/danilo/Go/src/gopkg.in/gin-gonic/gin.v1/context.go:97 (0x45d53a)
	(*Context).Next: c.handlers[c.index](c)
/home/danilo/Go/src/gopkg.in/gin-gonic/gin.v1/gin.go:284 (0x4638ce)
	(*Engine).handleHTTPRequest: context.Next()
/home/danilo/Go/src/gopkg.in/gin-gonic/gin.v1/gin.go:265 (0x4631b0)
	(*Engine).ServeHTTP: engine.handleHTTPRequest(c)
/usr/local/go/src/net/http/server.go:2202 (0x4e1fdd)
	serverHandler.ServeHTTP: handler.ServeHTTP(rw, req)
/usr/local/go/src/net/http/server.go:1579 (0x4de947)
	(*conn).serve: serverHandler{c.server}.ServeHTTP(w, w.req)
/usr/local/go/src/runtime/asm_amd64.s:2086 (0x45c0f1)
	goexit: BYTE	$0x90	// NOP

This is the function _getJSON, that returns a JSON-Encoded string of the results:

func _getJSON(sqlString string) (string, error) {
	rows, err := db.Query(sqlString)
	if err != nil {
		return "", err
	}
	defer rows.Close()
	columns, err := rows.Columns()
	if err != nil {
		return "", err
	}
	count := len(columns)
	tableData := make([]map[string]interface{}, 0)
	values := make([]interface{}, count)
	valuePtrs := make([]interface{}, count)
	for rows.Next() {
		for i := 0; i < count; i++ {
			valuePtrs[i] = &values[i]
		}
		rows.Scan(valuePtrs...)
		entry := make(map[string]interface{})
		for i, col := range columns {
			var v interface{}
			val := values[i]
			b, ok := val.([]byte)
			if ok {
				v = string(b)
			} else {
				v = val
			}
			entry[col] = v
		}
		tableData = append(tableData, entry)
	}
	jsonData, err := json.Marshal(tableData)
	if err != nil {
		return "", err
	}
	//fmt.Println(string(jsonData))
	return string(jsonData), nil
}