Issue
As my question states, I would like to know what we call types of queries with that type of condition in the WHERE
clause, i.e.:
SELECT * FROM mytable
WHERE (col1, col2) < (1, 2);
In other words:
Give me all records where col1
is less than '1' or if it equals '1' then col2
must be less than '2' - and none of the values are NULL.
I really like this type of syntax, but don't know what the naming convention is on how to refer to this type of condition. It looks like a tuple conditional but that name is not giving me anything from my searches.
My question stems from needing to know what this syntax is called in order to research how to write this using Criteria API with Hibernate and JPA2 and Postgres.
EDIT
I was able to write this using Criteria API using CriteriaBuilder's function() call:
//Our left expression (date, id)
Expression leftVal = criteriaBuilder.function("ROW", Tuple.class,
from.get("date").as(java.util.Date.class),
from.get("id").as(Long.class));
//Our right expression ex: ('2015-09-15', 32450)
ParameterExpression<Date> dateParam = criteriaBuilder.parameter(Date.class);
ParameterExpression<Long> idParam = criteriaBuilder.parameter(Long.class);
Expression rightVal = criteriaBuilder.function("ROW", Tuple.class, dateParam, idParam)
//build the first predicate using ROW expressions
Predicate predicate = criteriaBuilder.greaterThan(leftVal, rightVal);
//more query building happens
...
//construct final query and add parameters to our param expressions
TypedQuery<MyEntity> typedQuery = em.createQuery(criteriaQuery);
typedQuery.setParameter(dateParam, current.getDate());
typedQuery.setParameter(idParam, current.getId());
current
in this case is the record I retrieve as the row we want to get records BEFORE or AFTER. In this example I do after as noted by the greaterThan
function call.
Solution
The common short term is just "Row values". Or "Row value comparison" for the operation you demonstrate. That feature has been in the SQL standard since SQL-92 (!). Postgres is currently the only major RDBMS that supports it in all aspects - especially also with optimal index support.
In particular, the expression (col1, col2) < (1, 2)
is just shorthand for ROW(col1, col2) < ROW(1, 2)
in Postgres.
The expression ROW(col1, col2)
is also called row constructor - just like ARRAY[col1, col2]
is an array constructor.
It is conveniently short for the more verbose, equivalent expression:
col1 < 1 OR (col1 = 1 AND col2 < 2)
... and Postgres can use an index on (col1, col2)
or (col1 DESC, col2 DESC)
for this.
And notably distinct from: (!)
col1 < 1 AND AND col2 < 2
Consider example: (1,1)
...
Here is a presentation by Markus Winand that discusses the feature for pagination in detail:
"Pagination done the PostgreSQL way" on use-the-index-luke.com.
Row value comparison starts on page 20. The support matrix I have been referring to is on page 45.
I am in no way affiliated to Markus Winand.
Answered By - Erwin Brandstetter
Answer Checked By - Robin (JavaFixing Admin)