Complex conditional SQL statement in SQLite - sql

Question

I'm trying to build a support system in which I now face a complex query. I've got a couple tables in my SQLite table wich look like so (slightly simplified):
CREATE TABLE "assign" (
"id" INTEGER NOT NULL PRIMARY KEY,
"created" DATETIME NOT NULL,
"is_assigned" SMALLINT NOT NULL,
"user_id" INTEGER NOT NULL REFERENCES "user" ("id")
);
CREATE TABLE "message" (
"id" INTEGER NOT NULL PRIMARY KEY,
"created" DATETIME NOT NULL,
"user_id" INTEGER REFERENCES "user" ("id") ,
"text" TEXT NOT NULL
);
CREATE TABLE "user" (
"id" INTEGER NOT NULL PRIMARY KEY,
"name" VARCHAR(255) NOT NULL
);
I now want to do a query which gives me *a list of users for which the last created Assign.is_assigned == False and the last created Message is later than the last created Assign*. So I now have the following (pseudo) query:
SELECT *
FROM user
WHERE ((IF (
SELECT is_assigned
FROM assign
WHERE assign.user_id = user.id
ORDER BY created DESC LIMIT 1
) = False)
AND ((
SELECT created
FROM message
WHERE message.user_id = user.id
ORDER BY created DESC
LIMIT 1
) > (
SELECT created
FROM assign
WHERE assign.user_id = user.id
ORDER BY created DESC
LIMIT 1))
);
This makes sense to me, but unfortunately not to the computer. I guess I need to make use of case statements or even joins or something but I have no clue how. Does anybody have a tip on how to do this?

Answer 1

You don't need the IF in there, and SQLite has no False, but otherwise, your query is quite correct:
SELECT *
FROM "user"
WHERE NOT (SELECT is_assigned
FROM assign
WHERE user_id = "user".id
ORDER BY created DESC
LIMIT 1)
AND (SELECT created
FROM message
WHERE user_id = "user".id
ORDER BY created DESC
LIMIT 1
) > (
SELECT created
FROM assign
WHERE user_id = "user".id
ORDER BY created DESC
LIMIT 1)

Answer 2

Try following query I have created in mysql
SELECT u.id AS 'user',u.name AS 'User_Name', ass.created AS 'assign_created',ass.is_assigned AS 'is_assigned',
msg.created AS 'message_created'
FROM `user` AS u
LEFT JOIN `assign` AS ass ON ass.`user_id` = u.`id`
LEFT JOIN `message` AS msg ON msg.`user_id` = u.id
LEFT JOIN (SELECT u.id AS 'user_id',u.name AS 'username',ass.created AS 'max_ass_created',ass.is_assigned AS 'assigned'
FROM `user` AS u
LEFT JOIN `assign` AS ass ON ass.`user_id` = u.`id`
LEFT JOIN `message` AS msg ON msg.`user_id` = u.`id`
GROUP BY u.id ORDER BY ass.created DESC) AS sub ON sub.user_id = u.id
WHERE (sub.assigned IS FALSE AND msg.created < sub.max_ass_created)
check SQL Fiddle of your scenario
hope this will solve your problem !