inner-join

问题 In other words, for a nested/multiple JOIN SQL statement, is it safe to say that one should always use INNER JOIN first (either put it at the top line or by using parentheses to first INNER JOIN two tables) and make sure it precedes any OUTER JOIN ( LEFT , RIGHT , FULL )? My understanding is that matching columns (e.g., Primary Key column and Foreign Key column) usually don't have NULL values. And any non-matching rows including NULL from an OUTER JOIN result would be removed when being INNER

问题 I'm trying to update data in 2 distinct tables in the same query with the following code: UPDATE (SELECT s.passNumb, a.hour, a.minute, p.number, s.situation FROM passwords s JOIN atend a ON s.passNumb = a.passNumb JOIN points p ON a.number = p.number WHERE s.passNumb = 1 AND p.number = 1) SET a.hour = TO_CHAR(SYSDATE, 'HH24'), a.minute = TO_CHAR(SYSDATE, 'MI'), s.situation = 'F'; But I'm getting this error: Cannot modify a column which maps to a non key-preserved table . What am I doing wrong

问题 I have two tables (equipment & software) that I want to do an INNER JOIN on. They both have a field called EQCN. It is a text field. I get the following error: The data types text and text are incompatible in the equal to operator. There has to be a way around this. 回答1: Change the data types for these columns to varchar(max) . From Microsoft: ntext, text, and image data types will be removed in a future version of Microsoft SQL Server. Avoid using these data types in new development work,

问题 # example a <- data.frame(name=c("A","B","C"), KW=c(201902,201904,201905),price=c(1.99,3.02,5.00)) b <- data.frame(KW=c(201903,201904,201904),price=c(1.98,3.00,5.00),name=c("a","b","c")) I want to match a and b with fuzzy logic, using the variables KW and price. I want to allow a tolerance of +/- 1 for KW and a tolerance for +/- 0.02 in price. The desired outcome should look like this: name.x KW.x price.x KW.y price.y name.y 1 A 201902 1.99 201903 1.98 a 2 B 201904 3.02 201904 3.00 b 3 C

问题 # example a <- data.frame(name=c("A","B","C"), KW=c(201902,201904,201905),price=c(1.99,3.02,5.00)) b <- data.frame(KW=c(201903,201904,201904),price=c(1.98,3.00,5.00),name=c("a","b","c")) I want to match a and b with fuzzy logic, using the variables KW and price. I want to allow a tolerance of +/- 1 for KW and a tolerance for +/- 0.02 in price. The desired outcome should look like this: name.x KW.x price.x KW.y price.y name.y 1 A 201902 1.99 201903 1.98 a 2 B 201904 3.02 201904 3.00 b 3 C

问题 I have four models: articles , authors and tags . Each article can have many authors, and also can have many tags. So my DB will have the following tables: `article` `article_author` `author` `article_tag` `tags` Here in MySQL: DROP TABLE IF EXISTS article_tag; DROP TABLE IF EXISTS article_author; DROP TABLE IF EXISTS author; DROP TABLE IF EXISTS tag; DROP TABLE IF EXISTS article; CREATE TABLE IF NOT EXISTS author ( id INT(11) NOT NULL AUTO_INCREMENT, name VARCHAR(255), PRIMARY KEY (id) );

问题 I have four models: articles , authors and tags . Each article can have many authors, and also can have many tags. So my DB will have the following tables: `article` `article_author` `author` `article_tag` `tags` Here in MySQL: DROP TABLE IF EXISTS article_tag; DROP TABLE IF EXISTS article_author; DROP TABLE IF EXISTS author; DROP TABLE IF EXISTS tag; DROP TABLE IF EXISTS article; CREATE TABLE IF NOT EXISTS author ( id INT(11) NOT NULL AUTO_INCREMENT, name VARCHAR(255), PRIMARY KEY (id) );

问题 I have four models: articles , authors and tags . Each article can have many authors, and also can have many tags. So my DB will have the following tables: `article` `article_author` `author` `article_tag` `tags` Here in MySQL: DROP TABLE IF EXISTS article_tag; DROP TABLE IF EXISTS article_author; DROP TABLE IF EXISTS author; DROP TABLE IF EXISTS tag; DROP TABLE IF EXISTS article; CREATE TABLE IF NOT EXISTS author ( id INT(11) NOT NULL AUTO_INCREMENT, name VARCHAR(255), PRIMARY KEY (id) );

问题 I have the schema below. A quick explanation of it is: bob rated the movie up, 5/5 james rated the movie up, 1/5 macy rated the movie up, 5/5 No one has rated the movie avengers. The logic: If I am personA, look up everyone I have blocked. Look up all the movie reviews. Anyone who has left a movie review, and personA has blocked, remove them from the calculation. Calculate the average rating of the movies. CREATE TABLE movies ( id integer AUTO_INCREMENT primary key, name varchar(100) NOT NULL

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