选择3个具有计数和联接的表

Question

I've 3 tables tb1, users, users_credits. My gol is to combine two select (sel1, sel2) into a single view and display 0 in the sel2 where there isn't rows (left join?)

sel1

SELECT 
users.userid, 
users.datareg,
users_credits.credits,
FROM 
users,
users_credits,
WHERE
users.userid = users_credits.userid

Sel2

SELECT COUNT(*) FROM tb1 where tb1.id_user = users.userid

table structure

tb1
`id` int(11) NOT NULL AUTO_INCREMENT,
`id_user` decimal(11,0) NOT NULL,
`datains` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
PRIMARY KEY (`id`)

users

`userid` int(4) unsigned NOT NULL AUTO_INCREMENT,
`datareg` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
 PRIMARY KEY (`userid`)

users_credits

`id` int(11) NOT NULL AUTO_INCREMENT,
`userid` int(11) NOT NULL,
`credits` decimal(5,0) NOT NULL,
`data` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
PRIMARY KEY (`id`)

What is the best way to do this? Thanks.

Answer 1

SELECT  users.userid, 
        users.datareg,
        users_credits.credits,
        COALESCE(c.totalCount,0) totalCount
FROM    users
        LEFT JOIN users_credits
            ON users.userid = users_credits.userid
        LEFT JOIN
        (
            SELECT  id_user, COUNT(*) totalCount 
            FROM    tb1 
            GROUP   BY id_user
        ) c ON c.id_user = users.userid

To further gain more knowledge about joins, kindly visit the link below:

• Visual Representation of SQL Joins

UPDATE 1

SELECT  users.userid, 
        users.datareg,
        users_credits.credits,
        COALESCE(c.totalCount,0) totalCount,
        c.max_datains
FROM    users
        LEFT JOIN users_credits
            ON users.userid = users_credits.userid
        LEFT JOIN
        (
            SELECT  id_user, MAX(datains) max_datains, COUNT(*) totalCount 
            FROM    tb1 
            GROUP   BY id_user
        ) c ON c.id_user = users.userid

UPDATE 2

you need to create two views for this:

1st View:

CREATE VIEW tbl1View
AS
SELECT  id_user, MAX(datains) max_datains, COUNT(*) totalCount 
FROM    tb1 
GROUP   BY id_user

2nd View

CREATE VIEW FullView
AS
SELECT  users.userid, 
        users.datareg,
        users_credits.credits,
        COALESCE(c.totalCount,0) totalCount,
        c.max_datains
FROM    users
        LEFT JOIN users_credits
            ON users.userid = users_credits.userid
        LEFT JOIN tbl1View c ON c.id_user = users.userid