You could use id in (select id from …) or id in (select id from …) e.g. instead of non-working from Person p where p.name=”Joe” union from Person p join p.children c where c.name=”Joe” you could do from Person p where p.id in (select p1.id from Person p1 where p1.name=”Joe”) or p.id in (select p2.id … Read more
This is a very good question. I implemented the same algorithm on c# some time ago. The Algorithm constructs a common contour of two polygons (i.e. Constructs a union without holes). Here it is. Step 1. Create graph that describes the polygons. Input: first polygon (n points), second polygon (m points). Output: graph. Vertex – … Read more
You can do this by adding a pseudo-column named rank to each select, that you can sort by first, before sorting by your other criteria, e.g.: select * from ( select 1 as Rank, id, add_date from Table union all select 2 as Rank, id, add_date from Table where distance < 5 union all select … Read more
Just write Select id,name,age From Student Where age < 15 Union Select id,name,age From Student Where Name like “%a%” Order by name the order by is applied to the complete resultset
Quoting the docs, To apply ORDER BY or LIMIT to an individual SELECT, place the clause inside the parentheses that enclose the SELECT: (SELECT a FROM t1 WHERE a=10 AND B=1 ORDER BY a LIMIT 10) UNION (SELECT a FROM t2 WHERE a=11 AND B=2 ORDER BY a LIMIT 10);
Either the article you read used a bad example, or you misinterpreted their point. select username from users where company = ‘bbc’ or company = ‘itv’; This is equivalent to: select username from users where company IN (‘bbc’, ‘itv’); MySQL can use an index on company for this query just fine. There’s no need to … Read more
UNION puts lines from queries after each other, while JOIN makes a cartesian product and subsets it — completely different operations. Trivial example of UNION: mysql> SELECT 23 AS bah -> UNION -> SELECT 45 AS bah; +—–+ | bah | +—–+ | 23 | | 45 | +—–+ 2 rows in set (0.00 sec) … Read more
(The following applies when every row is SQL DISTINCT, and outside SQL code similarly treats NULL like just another value.) Every base table has a statement template, aka predicate, parameterized by column names, by which we put a row in or leave it out. We can use a (standard predicate logic) shorthand for the predicate … Read more
Here’s a plain implementation without using any third-party library. Main advantage over retainAll, removeAll and addAll is that these methods don’t modify the original lists input to the methods. public class Test { public static void main(String… args) throws Exception { List<String> list1 = new ArrayList<String>(Arrays.asList(“A”, “B”, “C”)); List<String> list2 = new ArrayList<String>(Arrays.asList(“B”, “C”, “D”, … Read more
You are trying to unpivot the data. MySQL does not have an unpivot function, so you will have to use a UNION ALL query to convert the columns into rows: select id, ‘a’ col, a value from yourtable union all select id, ‘b’ col, b value from yourtable union all select id, ‘c’ col, c … Read more