Keep Learning, Keep Growing

type Dummy struct { Name string `json:"name,omitempty"` Number int64 `json:"number,omitempty"` Pointer * string `json:"pointer,omitempty"` xxx string `json:"-"` // ignore this field yyy string `json:"-,"` // print this field with named - }

type account struct { id int name string age sql . NullInt64 amt sql . NullFloat64 } func testReadNullvalue ( db * sqlx . DB ) { rows , _ := db . Query ( "select id, name, age , amount from account" ) for rows . Next () { var foo account rows . Scan (& foo . id , & foo . name , & foo . age , & foo . amt ) if foo . amt . Valid == true { fmt . Println ( "value: %v" , foo . amt . Float64 ) } else { fmt . Println ( "data is null, print with default value " , foo . amt . Float64 ) } fmt . Println ( "%+v" , foo ) } }

https://www.postgresql.org/docs/9.6/plpgsql-declarations.html drop table account; --create table CREATE TABLE account(    id SERIAL PRIMARY KEY,    name VARCHAR NOT null,    age numeric,    amount numeric ); -- insert data into table INSERT INTO account (name,age,amount) values ('bonh',27,0); INSERT INTO account (name,age,amount) values ('kynp',27,0); --- select * from account SELECT * FROM account; -- delete record by id delete from account where id >= 3; SELECT * FROM account; -- procedure for tranfering drop procedure if exists transfer; CREATE OR REPLACE PROCEDURE transfer(INT, INT, DEC) LANGUAGE plpgsql  AS $$ BEGIN     -- subtracting the amount from the sender's account     UPDATE account     SET amount = amount - $3     WHERE id = $1;     -- adding the amount to the receiver's account     UPDATE account     SET amount = amount ...

Ref:  http://p.agnihotry.com/post/understanding_the_context_package_in_golang/

naturals := make ( chan int , 10 ) squares := make ( chan int ) go func () { for x := 0 ; ; x ++ { fmt . Println ( "Pushing" ) naturals <- x } }() go func () { for { fmt . Println ( "Getting out x" ) x := <- naturals squares <- x * x time . Sleep ( time . Second * 2 ) } }() for { fmt . Println (<- squares ) } naturals := make ( chan int , 10 ) As you can see that we use a buffered chan int with size 10 for naturals Then it can pushing to this chan maximum 10 element without waiting for getting out.

you should forget waitGroup :-) naturals := make ( chan int ) squares := make ( chan int ) go func () { for x := 0 ; ; x ++ { naturals <- x } }() go func () { for { x := <- naturals squares <- x * x } }() for { fmt . Println (<- squares ) } The above code is using unbuffered chan int. It means that that when naturals <-x then it must wait for getting x out by calling <-naturals then we can continue push naturals <-x. It is easy to say that it is not performance. In the next tutorial we will use buffered chan

it is simple wg := new ( sync . WaitGroup ) go func () { for i := 0 ; i < 10 ; i ++ { fmt . Println ( "Hello %d" , i ) time . Sleep ( time . Second / 2 ) } wg . Done () }() wg . Add ( 1 ) go func () { for i := 0 ; i < 10 ; i ++ { fmt . Println ( "Goodbye %d" , i ) time . Sleep ( time . Second ) } wg . Done () }() wg . Add ( 1 ) wg . Wait () Step 1: declare a wait group Step 2: at the end of task will will call wg.Done() to notify the task done Step 3: Specify exactly number of the task which need to wait for done by call wg.Add() If we have 3 task --> call wg.Add(3) or call 3 times wg.Add(1)