Just as the error says, the CREATE VIEW statement needs to be the only statement in the query batch. You have two option in this scenario, depending on the functionality you want to achieve: Place the CREATE VIEW query at the beginningCREATE VIEW showing as select tradename, unitprice, GenericFlag from Medicine; with ExpAndCheapMedicine(MostMoney, MinMoney) as ( select max(unitprice), min(unitprice) … Read more
Composite indexes work just like regular indexes, except they have multi-values keys. If you define an index on the fields (a,b,c) , the records are sorted first on a, then b, then c. Example:
The only portable way to achieve consistency between rooms and tags and making sure rooms are never returned after they had been deleted is locking them with SELECT FOR UPDATE. However in some systems locking is a side effect of concurrency control, and you achieve the same results without specifying FOR UPDATE explicitly. To solve this problem, Thread … Read more
This is a mix of HTML and code but it’s pretty basic, easy to understand and should be fairly simple to decouple to suit your needs I think.
Assuming that create_time contains the time the order was created, and you want the 100 clients with the latest orders, you can: add the create_time in your innermost query order the results of your outer query by the create_time desc add an outermost query that filters the first 100 rows using ROWNUM Query: UPDATE for Oracle 12c … Read more
Think of the null as “unknown” in that case (or “does not exist”). In either of those cases, you can’t say that they are equal, because you don’t know the value of either of them. So, null=null evaluates to not true (false or null, depending on your system), because you don’t know the values to … Read more
There are two formats of case expression. You can do CASE with many WHEN as; Or a Simple CASE expression Or CASE within CASE as;
Like the error says, row is a tuple, so you can’t do row[“pool_number”]. You need to use the index: row[0].
Short answer: Yes, it can be NULL or duplicate. I want to explain why a foreign key might need to be null or might need to be unique or not unique. First remember a Foreign key simply requires that the value in that field must exist first in a different table (the parent table). That … Read more