Why your code does not work? The where method returns an ActiveRecord::Relation object (acts like an array which contains the results of the where), it can be empty but it will never be nil. Business.where(id: -1) #=> returns an empty ActiveRecord::Relation ( similar to an array ) Business.where(id: -1).nil? # ( similar to == nil? … Read more
SELECT * FROM B WHERE NOT EXISTS (SELECT 1 FROM A WHERE A.ID = B.ID)
Looking at the official make documentation, here is a good way to do it: OBJDIR := objdir OBJS := $(addprefix $(OBJDIR)/,foo.o bar.o baz.o) $(OBJDIR)/%.o : %.c $(COMPILE.c) $(OUTPUT_OPTION) $< all: $(OBJS) $(OBJS): | $(OBJDIR) $(OBJDIR): mkdir -p $(OBJDIR) You should see here the usage of the | pipe operator, defining an order only prerequisite. Meaning … Read more
If you don’t want to execute SQL directly, the best way is to use Any(). This is because Any() will return as soon as it finds a match. Another option is Count(), but this might need to check every row before returning. Here’s an example of how to use it: if (context.MyEntity.Any(o => o.Id == … Read more
Yeah, it’s possible using $exists: db.things.find( { a : { $exists : false } } ); // return if a is missing When is true, $exists matches the documents that contain the field, including documents where the field value is null. If is false, the query returns only the documents that do not contain the … Read more
is_file() will return false if the given path points to a directory. file_exists() will return true if the given path points to a valid file or directory. So it would depend entirely on your needs. If you want to know specifically if it’s a file or not, use is_file(). Otherwise, use file_exists().
If the sent_at field is not there when its not set then: db.emails.count({sent_at: {$exists: false}}) If it’s there and null, or not there at all: db.emails.count({sent_at: null}) If it’s there and null: db.emails.count({sent_at: { $type: 10 }}) The Query for Null or Missing Fields section of the MongoDB manual describes how to query for null … Read more
EXISTS will be faster because once the engine has found a hit, it will quit looking as the condition has proved true. With IN, it will collect all the results from the sub-query before further processing.
Your status-codes are also a collection, so use Contains: var allowedStatus = new[]{ “A”, “B”, “C” }; var filteredOrders = orders.Order.Where(o => allowedStatus.Contains(o.StatusCode)); or in query syntax: var filteredOrders = from order in orders.Order where allowedStatus.Contains(order.StatusCode) select order;
You can’t return two (or multiple) columns in your subquery to do the comparison in the WHERE A_ID IN (subquery) clause – which column is it supposed to compare A_ID to? Your subquery must only return the one column needed for the comparison to the column on the other side of the IN. So the … Read more