inner-join

问题 I'm implementing API using Sequelize in node.js. I have three tables i.e. users, projects and userprojects. Here, userprojects table contains foreign key columns i.e. UserId and ProjectId from users and projects table respectively (as shown in picture below) I want to inner join userprojects and projects table so I get final flat result as Project Id (from userproject table) and Project Name (from project table) in a flat format e.g. 7AD60938-60F5-433D-A55B-2F48A9931EFA | Project 01 2582A40C

问题 I have two tables. Table 1: +------------+-------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +------------+-------------+------+-----+---------+-------+ | ID | varchar(255)| NO | PRI | NULL | | | Sex | int(20) | YES | | NULL | | | Age | varchar(255)| YES | | NULL | | +------------+-------------+------+-----+---------+-------+ Table 2: +-----------+--------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +--------

问题 The following image can be found by searching for SQL join on the internet: Can we interpret this as a Venn diagram, in the following way? The circle labelled Table A is the set of records in Table A The circle labelled Table B is the set of records in Table B The intersection of the sets represents inner join (aka just join in SQL) Motivation The diagram shown, which appears in various forms widely on the net, looks awfully like a Venn diagram. So the first intuition is to think of it as a

问题 I have two tables, which have the same columns except for 1. So for example: Table1 (column names): Student | Course | Exam1 | Exam2 Table2 (column names): Student | Course | Exam3 | FinalExam I would like to combine these two tables to get: Table: Student | Course | Exam1 | Exam2 | FinalExam I have something along the following: Select student, course, Exam1, Exam2 From Table1 Select student, course, Exam3, FinalExam From Table2 Select student, course, Coalesce( t1.Exam1, 0) as Exam1

问题 In my opinion these two SELECTs are exactly equal (but I want to rewrite the first for the second to help the optimizer in my case) - whatever data sits in tables a,b,c,d both SELECTs will produce exactly the same results. Do you agree? Thanks! create table a (id number); create table b (id number); create table c (id number); create table d (id number); --Q1 select * from a,b,c,d where a.id = b.id and a.id = c.id and a.id = d.id; --Q2 select * from a,b,c,d where a.id = b.id and a.id = c.id

问题 How to exclude records from results when ID from A table is in PID column of B table for the same PUIDenter image description here Table A: PUID PID SYSTEMCODE ID 100000 701848421 A 3207479 Table B: PUID PID SYSTEMCODE 100000 3207479 B 100000 6805875 B 回答1: Use not exists : select a.* from tablea a where not exists (select 1 from tableb b where b.pid = a.id and b.puid = a.puid) 来源： https://stackoverflow.com/questions/64794523/how-to-exclude-records-from-results-when-id-from-a-table-is-in-pid

问题 I have two SQL tables. One gets a reference value from another table which stores a list of Modules and their ID. But these descriptions are not unique. I am trying to remove the duplicates of Table A but I'm not sure how to update Table B to only reference the single values. Example: Table A: Table B: -------------------------------- ------------------------------------ ID Description RefID ID Name -------------------------------- ------------------------------------ 1 Test 1 2 1

问题 I'm working on a system, and this module is supposed to echo the contents of the database. It worked perfectly until I added some JOIN statements to it. I've checked and tested the SQL code, and it works perfectly. What's not working is that part where I echo the content of the JOINed table. My code looks like this: $query = "SELECT reg_students.*, courses.* FROM reg_students JOIN courses ON reg_students.course_id = courses.course_id WHERE reg_students.user_id = '".$user_id."'"; $result =

问题 let's say that there're 2 tables (in oracle SQL) like this: user(user_id, company_id): 123 | company_id_1 | 123 | company_id_2 | company(id, version_id): company_id_1 | (null) | company_id_2 | version_id1 | the following query returns 2 rows company_id_1 company_id_2 SELECT distinct(company_id) FROM user WHERE user.user_id = 123 AND user.company_id IS NOT NULL AND EXISTS (SELECT 1 FROM company INNER JOIN user ON company.id = user.company_id AND company.version_id IS NOT NULL); I would expect

问题 let's say that there're 2 tables (in oracle SQL) like this: user(user_id, company_id): 123 | company_id_1 | 123 | company_id_2 | company(id, version_id): company_id_1 | (null) | company_id_2 | version_id1 | the following query returns 2 rows company_id_1 company_id_2 SELECT distinct(company_id) FROM user WHERE user.user_id = 123 AND user.company_id IS NOT NULL AND EXISTS (SELECT 1 FROM company INNER JOIN user ON company.id = user.company_id AND company.version_id IS NOT NULL); I would expect