sql-order-by

I have the following table: id time text otheridentifier ------------------------------------------- 1 6 apple 4 2 7 orange 4 3 8 banana 3 4 9 pear 3 5 10 grape 2 What I want to do is select the 3 most recent records (by time desc), whose otheridentifier s are distinct. So in this case, the result would be id 's: 5, 4, and 2. id = 3 would be skipped because there's a more recent record with the same otheridentifier field. Here's what I tried to do: SELECT * FROM `table` GROUP BY (`otheridentifier`) ORDER BY `time` DESC LIMIT 3 However, I end up getting rows of id = 5, 3 , and 1 instead of 5, 4

I have a SQL table with a datetime field. The field in question can be null. I have a query and I want the results sorted ascendingly by the datetime field, however I want rows where the datetime field is null at the end of the list, not at the beginning. Is there a simple way to accomplish that? select MyDate from MyTable order by case when MyDate is null then 1 else 0 end, MyDate (A "bit" late, but this hasn't been mentioned at all) You didn't specify your DBMS. In standard SQL (and most modern DBMS like Oracle, PostgreSQL, DB2, Firebird, Apache Derby, HSQLDB and H2) you can specify NULLS

Here's the query (the largest table has about 40,000 rows) SELECT Course.CourseID, Course.Description, UserCourse.UserID, UserCourse.TimeAllowed, UserCourse.CreatedOn, UserCourse.PassedOn, UserCourse.IssuedOn, C.LessonCnt FROM UserCourse INNER JOIN Course USING(CourseID) INNER JOIN ( SELECT CourseID, COUNT(*) AS LessonCnt FROM CourseSection GROUP BY CourseID ) C USING(CourseID) WHERE UserCourse.UserID = 8810 If I run this, it executes very quickly (.05 seconds roughly). It returns 13 rows. When I add an ORDER BY clause at the end of the query (ordering by any column) the query takes about 10

As I know, from the relational database theory, a select statement without an order by clause should be considered has not particular order. But actually in SQL Server and Oracle (I've tested on those 2 platforms), if I query from a table without an order by clause multiple times, I always get the results in the same order. Does this behavior can be relied on? Anyone can help to explain a little? SingleNegationElimination No, that behavior cannot be relied on. The order is determined by the way the query planner has decided to build up the result set. simple queries like select * from foo

Assume that the following query is issued to a MySQL database: SELECT * FROM table_name; Note that no ORDER BY clause is given. My question is: Does MySQL give any guarantees to which order the result set rows will be given? More specifically, can I assume that the rows will be returned in insertion order?, that is the same order in which the rows were inserted into the table. No, there are no guarantees. Unless you specify an order using an ORDER BY clause, the order is totally dependent on internal implementation details. I.e. whatever is most convenient for the RDBMS engine. In practice,