What is SQL JOIN ? SQL JOIN is a method to retrieve data from two or more database tables. What are the different SQL JOINs ? There are a total of five JOINs. They are : 1. JOIN or INNER JOIN 2. OUTER JOIN 2.1 LEFT OUTER JOIN or LEFT JOIN 2.2 RIGHT OUTER JOIN … Read more
They are functionally equivalent, but INNER JOIN can be a bit clearer to read, especially if the query has other join types (i.e. LEFT or RIGHT or CROSS) included in it.
Joins are used to combine two related tables together. In your example, you can combine the Employee table and the Department table, like so: SELECT FNAME, LNAME, DNAME FROM EMPLOYEE INNER JOIN DEPARTMENT ON EMPLOYEE.DNO=DEPARTMENT.DNUMBER This would result in a recordset like: FNAME LNAME DNAME —– —– —– John Smith Research John Doe Administration I … Read more
Shortly, you can’t do that (at least for SqlServer). The explanation is contained in EF Core documentation – Raw SQL Queries – Composing with LINQ: Composing with LINQ requires your raw SQL query to be composable since EF Core will treat the supplied SQL as a subquery. SQL queries that can be composed on begin … Read more
I like to call this problem “cross join by proxy”. Since there is no information (WHERE or JOIN condition) how the tables department and contact are supposed to match up, they are cross-joined via the proxy table person – giving you the Cartesian product. Very similar to this one: Two SQL LEFT JOINS produce incorrect … Read more
The key word here is FIRST. You can use analytic function FIRST_VALUE or aggregate construct FIRST. For FIRST or LAST the performance is never worse and frequently better than the equivalent FIRST_VALUE or LAST_VALUE construct because we don’t have a superfluous window sort and as a consequence a lower execution cost: select table_A.id, table_A.name, firstFromB.city … Read more
Try: SELECT WO_BreakerRail.ID, indRailType.RailType, WO_BreakerRail.CreatedPieces, WO_BreakerRail.OutsideSource, WO_BreakerRail.Charged, WO_BreakerRail.Rejected, WO_BreakerRail.RejectedToCrop FROM indRailType LEFT OUTER JOIN WO_BreakerRail ON indRailType.RailCode = WO_BreakerRail.RailCode AND WO_BreakerRail.Date = @Date Thus adding AND WO_BreakerRail.Date = @Date onto the join
First: Foreign key relationship are not only for navigating. They mainly serve to ensure that no spurious values are introduced in the relationship. They also may help the database for query optimization. I would advise you to reconsider that. Anyway, for creating a query that uses several unrelated entities, you need to put them as … Read more
If I understand well the issue, you are looking for the concat function. pandas.concat([df1, df2, df3, df4]) should work correctly if the column names are the same for both dataframes.
Here’s a typical way to do this query without using the subquery method you showed. This may satisfy @Godeke’s request to see a join-based solution. SELECT * FROM movies m LEFT OUTER JOIN seen s ON (m.id = s.movie_id AND s.user_id = 123) WHERE s.movie_id IS NULL; However, in most brands of database this solution … Read more