compound-key

Can I get the LAST INSERT ID() for a compound key in MySQL? Yes. You can't have multiple auto-increment fields in a single table. CREATE TABLE foo ( id1 int(11) NOT NULL auto_increment, id2 int(11) NOT NULL default '0', PRIMARY KEY (id1, id2) ); INSERT INTO foo VALUES (DEFAULT, 2); SELECT LAST_INSERT_ID(); -- returns 1, the value generated for id1 LAST_INSERT_ID() returns the value only for a column declared AUTO_INCREMENT . There's no function to return the value in a compound primary key that wasn't generated by the system. You ought to know that value already, since you just gave it in an

I've read that compound primary keys will confuse the hell out of typical ORM code generators . Which ORMs work best with compound PKs and which to avoid? (I've a particular interest in .NET) I'm using NHibernate successfully with compound keys. <class name="UserProfileField" table="UserProfileFields"> <composite-id> <key-many-to-one name="Parent" column="UserId" lazy="false"/> <key-property name="FieldName"/> </composite-id> ... 来源： https://stackoverflow.com/questions/218100/orm-support-for-compound-primary-keys

I want to start using dplyr in place of ddply but I can't get a handle on how it works (I've read the documentation). For example, why when I try to mutate() something does the "group_by" function not work as it's supposed to? Looking at mtcars: library(car) Say I make a data.frame which is a summary of mtcars, grouped by "cyl" and "gear": df1 <- mtcars %.% group_by(cyl, gear) %.% summarise( newvar = sum(wt) ) Then say I want to further summarise this dataframe. With ddply, it'd be straightforward, but when I try to do with with dplyr, it's not actually "grouping by": df2 <- df1 %.% group_by

I can find syntax "charts" on this on the SQLite website, but no examples and my code is crashing. I have other tables with unique constraints on a single column, but I want to add a constraint to the table on two columns. This is what I have that is causing an SQLiteException with the message "syntax error". CREATE TABLE name (column defs) UNIQUE (col_name1, col_name2) ON CONFLICT REPLACE I'm doing this based on the following: table-constraint To be clear, the documentation on the link I provided says that CONTSTRAINT name should come before my constraint definition. Something that may lead