left-join

问题 Yesterday I gave this answer: Matching Data Tables by five columns to change a value in another column. In the comments, the OP asked if we could effectively achieve a left join of the two tables and thereby get the NAs that would result in the right table to be assigned to the left table. It seems to me that data.table does not provide any means of doing this. Here's the example case I used in that question: set.seed(1L); dt1 <- data.table(id=1:12,expand.grid(V1=1:3,V2=1:4),blah1=rnorm(12L))

问题 I am using SQL Server (I believe it is 2005). I have TableA that has 2 columns and 439 rows (each row is unique). +----------+ |ID | Name | +----------+ I have TableB that has 35 columns and many hundreds of thousand rows (each row is also unique). +------------------------------------------------------------------------------+ |Date | ID | Name | Blah1 | Blah2 | ... | Hour1 | Hour2 | Hour3 | ... | Hour24 | +------------------------------------------------------------------------------+ Each

问题 Given this table: SELECT * FROM CommodityPricing order by dateField "SILVER";60.45;"2002-01-01" "GOLD";130.45;"2002-01-01" "COPPER";96.45;"2002-01-01" "SILVER";70.45;"2003-01-01" "GOLD";140.45;"2003-01-01" "COPPER";99.45;"2003-01-01" "GOLD";150.45;"2004-01-01" "MERCURY";60;"2004-01-01" "SILVER";80.45;"2004-01-01" As of 2004, COPPER was dropped and mercury introduced. How can I get the value of (array_agg(value order by date desc) ) [1] as NULL for COPPER ? select commodity,(array_agg(value

问题 $lookup is new in MongoDB 3.2. It performs a left outer join to an unsharded collection in the same database to filter in documents from the “joined” collection for processing. To use $lookup , the from collection cannot be sharded. On the other hand, sharding is a useful horizontal scaling approach. What's the best practise to use them together? 回答1: As the docs you quote indicate, you can't use $lookup on a sharded collection. So the best practice workaround is to perform the lookup

问题 Similar to this question, but their problem with the query was never fully solved: #Error showing up in multiple LEFT JOIN statement Access query when value should be NULL I get #Error when I'm expecting to see a Null when doing a left join where there is no corresponding record on the right hand side of the join: Chain CasesPerMonthPerStore MonthOfFirstOrder Naturally 2.3 5/1/2011 Tom's Market #Error Livingstons #Error EverClear 3.1 7/1/2012 Bob's Market 2.66 5/1/2012 Andy's Exports #Error

问题 i have 2 tables areas2013 row_id | area |teamleader 1 | 1234-Asia | Joe 2 | 12345-Europe | Juan 3 | 123456-UK | Ple and f12 row_id| eacode 1 | 1234 2 | 12345 3 | 1234 as you can see i want to match the eacode and area using like% and count how many eacode. i want something like this in php eacode| area | count | teamleader 1234 | Asia | 2 | Joe 12345 | Europe| 1 | Juan sorry for my bad english 回答1: Barmar's answer is good I just tweaked it a bit to get the exact output you requested: SELECT

问题 I am trying to make it so that this query below counts rows from another table that have the username, then deaths that have killer. There is 1 row per username in the stats table, but multiple rows with in the pvp table with the username. The deaths column is the same amount as the kills column for some reason, does anyone know why? Here is my query. Here is a sql fiddle I think I got it right idk how to use sqlfiddle: http://sqlfiddle.com/#!2/b793b/1 SELECT *, COUNT(pvptable.killer) as

问题 Defined model and classes protected override void OnModelCreating(ModelBuilder modelBuilder) { base.OnModelCreating(modelBuilder); modelBuilder.Entity<RootLink>() .HasOne(link => link.Node) .WithMany(node => node.RootLinks) .HasForeignKey(link => link.NodeId); modelBuilder.Entity<RootLink>() .HasOne(link => link.RootNode) .WithMany() .HasForeignKey(rootLink => rootLink.RootNodeId) .OnDelete(DeleteBehavior.Restrict); modelBuilder.Entity<NodeLink>() .HasOne(link => link.Node) .WithMany(node =>

问题 I have php-script running on top of apache. Every time when user goes to specific URL, he/she will get csv-file. Column names are fetched like this (thanks to Daniel Figueroa :) $csv_output .= "\n"; // get the column name from the first DB (ins.data) mysql_select_db($db, $link) or die("Can not connect to DB1."); $result = mysql_query("SHOW COLUMNS FROM ".$table." WHERE Field NOT IN ('ID','Key','Text')"); $i = 0; if (mysql_num_rows($result) > 0) { while ($row = mysql_fetch_assoc($result)) {

问题 I'm trying to get deeper into "advanced"-SQL'ing but have a slight problem with some pretty basic stuff. I have one table, where one row refers to another row. There are of course unique id's as well but I'll skip those here: +----------+----------------------------+ | field | name | value | +----------+----------------------------+ | 1 | aa | 0 | | 1 | ab | 0 | | 2 | ba | 1 | | 2 | bb | 1 | | 3 | ca | 2 | | 3 | cb | 2 | +----------+----------------------------+ What I want to accomplish is