![]() You must use nested select statements to write this query.Ĭ)Write the previous query using join operations. Report the user names of the tweeter and retweeter (the person who retweeted the tweet) as well as the tweet text and date.ī)Find all distinct users (userName and city) who follow a user who follow user “Yoshua Bengio”. (12,'Rhonda Ferguson', 'NY', ' 11:41:26-08') Ī)Find all users who retweeted a tweet that was tagged with “#Iphone” after 2015. 18 It is designed to handle a range of workloads, from single machines to data warehouses or Web services with many concurrent users. (9,'Betty Summers', 'Paris', ' 11:41:26-08'), PostgreSQL features transactions with Atomicity, Consistency, Isolation, Durability (ACID) properties, automatically updatable views, materialized views, triggers, foreign keys, and stored procedures. When Pg creates an implicit index it will emit a NOTICE -level message that you can see in psql and/or the system logs, so you can see when it happens. (7,'Andrew Ng', 'Frankfurt', ' 14:41:26-08'), PostgreSQL automatically creates indexes on primary keys and unique constraints, but not on the referencing side of foreign key relationships. My query is as follows SELECT C.CREATE TABLE Users ( userId SERIAL PRIMARY KEY, userName VARCHAR, city VARCHAR, lastLogin TIMESTAMP ) ĬREATE TABLE Tweets ( tweetId SERIAL PRIMARY KEY, userId INT NOT NULL REFERENCES Users ( userId ), tweetTimestamp TIMESTAMP NOT NULL, tweetText VARCHAR ) ĬREATE TABLE Retweets ( userId INT REFERENCES Users ( userId ), tweetId INT REFERENCES Tweets ( tweetId ), retweetTimestamp TIMESTAMP, PRIMARY KEY ( userId, tweetId, retweetTimestamp )) ĬREATE TABLE TweetTags ( tweetId INT, hashtag VARCHAR CHECK ( hashtag LIKE '#%'), PRIMARY KEY ( tweetId, hashtag )) ĬREATE TABLE Follows ( followerId INT REFERENCES Users ( userId ), followeeId INT REFERENCES Users ( userId ), PRIMARY KEY ( followerId, followeeId )) ![]() I have written a sql query with basic knowledge that returns now primary columns but when coming to foreign keys doesn't work (it retrieving the columns which are having foreign keys) So i decided to create a procedure that takes all the non constraint column as input and append there table name with column names. I used to create aliases for each and every column every time when i need to import tables from oracle. It doesn't allow the columns which are of same name in two different tables. I am really new to Stackoverflow apologies for any mistakes. Use References to Impose a Foreign Key Relationship in PostgreSQL So let’s begin creating our two tables. More generally, you need to make sure that the column or columns you have in your REFERENCES clause match exactly a unique index in the parent table: in your case it fails because you do not have a single unique index on Title alone. Today, we’ll be learning how to use FOREIGN KEYS in PostgreSQL. If you need to keep your primary key as ISBN, Title then you either need to store the ISBN in BookCopy as well as the Title, and foreign key on both columns, OR you need to create a unique index on BookTitle(Title) as a distinct index. ON the assumption this is the case, then change your primary key to be only on ISBN, and change BookCopy so that instead of Title you have ISBN and join on that. I would hazard a guess that the ISBN is unique for each row in BookTitle. ![]() There are a number of options open to you, depending on exactly what BookTitle holds and the relationship of the data within it. Foreign keys work by joining a column to a unique key in another table, and that unique key must be defined as some form of unique index, be it the primary key, or some other unique index.Īt the moment, the only unique index you have is a compound one on ISBN, Title which is your primary key.
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