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How to use SUM inside COALESCE in JOOQ

Given below is a gist of the query, which I'm able to run successfully in MySQL
SELECT a.*,
COALESCE(SUM(condition1 or condition2), 0) as countColumn
FROM table a
-- left joins with multiple tables
GROUP BY a.id;
Now, I'm trying to use it with JOOQ.
ctx.select(a.asterisk(),
coalesce(sum("How to get this ?")).as("columnCount"))
.from(a)
.leftJoin(b).on(someCondition)
.leftJoin(c).on(someCondition))
.leftJoin(d).on(someCondition)
.leftJoin(e).on(someCondition)
.groupBy(a.ID);
I'm having a hard time preparing the coalesce() part, and would really appreciate some help.

jOOQ's API is more strict about the distinction between Condition and Field<Boolean>, which means you cannot simply treat booleans as numbers as you can in MySQL. It's usually not a bad idea to be explicit about data types to prevent edge cases, so this strictness isn't necessarly a bad thing.
So, you can transform your booleans to integers as follows:
coalesce(
sum(
when(condition1.or(condition2), inline(1))
.else_(inline(0))
),
inline(0)
)
But even better than that, why not use a standard SQL FILTER clause, which can be emulated in MySQL using a COUNT(CASE ...) aggregate function:
count().filterWhere(condition1.or(condition2))

Add limit and offset to query that was created from a String

I have query as String like
select name from employee
and want to limit the number of rows with limit and offset.
Is this possible with jOOQ and how do I do that?
Something like:
dsl.fetch("select name from employee").limit(10).offset(10);

Yes you're close, but you cannot use fetch(sql), because that eagerly executes the query and it will be too late to append LIMIT and OFFSET. I generally don't recommend the approach offered by Sergei Petunin, because that way, you will tell the RDBMS less information about what you're going to do. The execution plan and resource allocations are likely going to be better if you actually use LIMIT and OFFSET.
There are two ways to do what you want to achieve:
Use the parser
You can use DSLContext.parser() to parse your SQL query and then modify the resulting SelectQuery, or create a derived table from that. Creating a derived table is probably a bit cleaner:
dsl.selectFrom(dsl.parser().parse("select name from employee"))
.limit(10)
.offset(10)
.fetch();
The drawback is that the parser will have to understand your SQL string. Some vendor specific features will no longer be available.
The advantage (starting from jOOQ 3.13) is that you will be able to provide your generated code with attached converters and data type bindings this way, as jOOQ will "know" what the columns are.
Use plain SQL
You were already using plain SQL, but the wrong way. Instead of fetching the data eagerly, just wrap your query in DSL.table() and then use the same approach as above.
When using plain SQL, you will have to make sure manually, that the resulting SQL is syntactically correct. This includes wrapping your query in parentheses, and possibly aliasing it, depending on the dialect you're using:
dsl.selectFrom(table("(select name from employee)").as("t"))
.limit(10)
.offset(10)
.fetch();

The best thing you can do with a string query is to create a ResultQuery from it. It allows you to limit the maximum amount of rows fetched by the underlying java.sql.Statement:
create.resultQuery("select name from employee").maxRows(10).fetch();
or to fetch lazily and then scroll through the cursor:
create.resultQuery("select name from employee").fetchLazy().fetch(10);
Adding an offset or a limit to a query is only possible using a SelectQuery, but I don't think there's any way to transform a string query to a SelectQuery in JOOQ.
Actually, if you store SQL queries as strings in the database, then you are already in a non-typesafe area, and might as well append OFFSET x LIMIT y directly to a string-based query. Depending on the complexity of your queries, it might work.

How to determine if a table contains a value in SQL?

I feel like I'm missing something very obvious here, but it seems that the only way to go about doing this is to get the value, and then see if it returns a null (empty) value, which I would rather not do.
Is there an equivalent to List.contains(Object o) in SQL? Or perhaps the JDBC has something of that nature? If so, what is it?
I am using Microsoft Access 2013.
Unfortunately I don't have any useful code to show, but here is the gist of what I am trying to do. It isn't anything unique at all. I want to have a method (Java) that returns the values of a user that are stored in the database. If the user has not previously been added to the database, the user should be added, and the default values of the user should be set. Then those newly created values will be returned. If a player has already been added to the database (with the username as the primary key), I don't want to overwrite the data that is already there.
I would also advise against using MS Access for this purpose, but if you are familiar with MS Office applications, the familiar UI/UX structure might help you get your footing and require less time to learn other database environments. However, MS Access tends to be quite limited, and I would advise considering alternative options if available.

The only way to see if an SQL table contains a row with some condition on a column is to actually make an SQL query. I don't see why you wouldn't do that. Just make sure that you have an index on the column that you will be constraining the results on. Also for better speed use count to prevent from retrieving all the data from the rows.
SELECT count(*) FROM foos WHERE bar = 'baz'
Assuming you have an index on the bar column this query should be pretty fast and all you have to do is check whether it returns > 0. If it does then you have rows matching your criteria.

You can use "IF EXISTS" which returns a boolean value of 1 or 0.
select
if(
exists( select * from date1 where current_date()>now() ),
'today > now',
'today is not > now'
) as 'today > now ?' ;
+--------------------+
| today > now? |
+--------------------+
| today is not > now |
+--------------------+
1 row in set (0.00 sec)
Another Example:
SELECT IF(
EXISTS( SELECT col from tbl where id='n' ),
colX, colY
) AS 'result'
FROM TBL;

I'm also new to sql and I'm using Oracle.
In Oracle, suppose we have: TYPE: value.
We can use:
where value not in (select TYPE from table)
to make sure value not exist in the column TYPE of the table.
Don't know if it helps.

You can simply use Query with condition.
For example if you have to check records with particular coloumn, you can use where condition
select * from table where column1 = 'checkvalue'
You can use count property to check the no. of records existing with your specified conditon
select count(*) from table where column1 = 'checkvalue'

I have created the following method, which to my knowledge works perfectly. (Using the java.sql package)
public static containsUser(String username)
{
//connection is the Connection object used to connect to my Access database.
Statement statement = this.connection.createStatement();
//"Users" is the name of the table, "Username" is the primary key.
String sql = "SELECT * FROM Users WHERE Username = '" + username + "'";
Result result = statement.executeQuery(sql);
//There is no need for a loop because the primary key is unique.
return result.next();
}
It's an extremely simple and extremely basic method, but hopefully it might help someone in the future.
If there is anything wrong with it, please let me know. I don't want anyone learning from or using poorly written code.
IMPORTANT EDIT: It is now over half a decade after I wrote the above content (both question and answer), and I now advise against the solution I illustrated above.
While it does work, it prioritizes a "Java-mindset-friendly" approach to SQL. In short, it is typically a bad idea to migrate paradigms and mindsets of one language to another, as it is inevitable that you will eventually find yourself trying to fit a square peg into a round hole. The only way to make that work is to shave the corners off the square. The peg will then of course fit, but as you can imagine, starting with a circle peg in the first place would have been the better, cleaner, and less messy solution.
Instead, refer to the above upvoted answers for a more realistic, enterprise-friendly solution to this problem, especially as I imagine the people reading this are likely in a similar situation as I was when I originally wrote this.

GAE - Java - Best way to do a query filter "LIKE"

In my GAE Datastore I have "Person" Entity with name, surname and country
I need to do a query like
"SELECT * FROM Country WHERE name LIKE '%spa%'"
This answer offers a solution like this:
Query query = new Query("Person");
query.addFilter("name", FilterOperator.GREATER_THAN_OR_EQUAL, "pe");
query.addFilter("name", FilterOperator.LESS_THAN, "pe"+ "\uFFFD");
But I don't have any success, always return 0 results... I'm missing something?
It seems that another alternative is useing the "Search API", but... How I migrate all my data of "Persons" in my Datastore to a new Document to do the search?
Any solutions?
Thanks

That answer is not the same as your question. The query they provide is a prefix query: ie all names that start with "pe". You seem to want a query for all names which contain "pe" anywhere, which is not possible for the reasons explained in the accepted answer to that question.
The Search API is indeed the answer to doing this, and the details of how to create documents to represent your datastore objects are contained in the link you posted. (Note this isn't a migration: your data should stay in the datastore, the Search API is a separate system used only for full-text search.)

Hibernate getting position of a row in a result set

I need to get an equivalent to this SQL that can be run using Hibernate. It doesn't work as is due to special characters like #.
SELECT place from (select #curRow := #curRow + 1 AS place, time, id FROM `testing`.`competitor` JOIN (SELECT #curRow := 0) r order by time) competitorList where competitorList.id=4;
My application is managing results of running competitions. The above query is selecting for a specific competitor, it's place based on his/her overall time.
For simplicity I'll only list the COMPETITOR table structure (only the relevant fields). My actual query involves a few joins, but they are not relevant for the question:
CREATE TABLE competitor {
id INT,
name VARCHAR,
time INT
}
Note that competitors are not already ordered by time, thus, the ID cannot be used as rank. As well, it is possible to have two competitors with the same overall time.
Any idea how I could make this work with Hibernate?

Hard to tell without a schema, but you may be able to use something like
SELECT COUNT(*) FROM testing ts
WHERE ts.score < $obj.score
where I am using the $ to stand for whatever Hibernate notation you need to refer to the live object.

I couldn't find any way to do this, so I had to change the way I'm calculating the position. I'm now taking the top results and am creating the ladder in Java, rather than in the SQL query.