How to Use SQL INTERSECT to Work Around SQL’s NULL Logic

ANOTHER SQL Post this week? I got nerd-sniped: https://twitter.com/rafaelcodes/status/870574075244158980 Oooooh, challenge accepted! So, let's assume we have a table T with columns (A, B, C) like this: WITH t(a, b, c) AS ( SELECT 'a', 'b', null FROM dual UNION ALL SELECT 'a', null, 'c' FROM dual UNION ALL SELECT 'a', 'b', 'c' FROM dual … Continue reading How to Use SQL INTERSECT to Work Around SQL’s NULL Logic

SQL IN Predicate: With IN List or With Array? Which is Faster?

Hah! Got nerd-sniped again: http://stackoverflow.com/questions/43099226/how-to-make-jooq-to-use-arrays-in-the-in-clause/43102102 A jOOQ user was wondering why jOOQ would generate an IN list for a predicate like this: Java COLUMN.in(1, 2, 3, 4) SQL COLUMN in (?, ?, ?, ?) ... when in fact there could have been the following predicate being generated, instead: COLUMN = any(?::int[]) In the second case, … Continue reading SQL IN Predicate: With IN List or With Array? Which is Faster?

SQL JOIN or EXISTS? Chances Are, You’re Doing it Wrong

I've noticed this very consistently with a lot of customers, and also with participants of our Data Geekery SQL Workshop (which I highly recommend to everyone, if you excuse the advertising): A lot of developers get the distinction between JOIN and SEMI-JOIN wrong. Let me explain... What are JOIN and SEMI-JOIN A little bit of … Continue reading SQL JOIN or EXISTS? Chances Are, You’re Doing it Wrong

INTERSECT – the Underestimated Two-Way IN Predicate

Have you ever wondered how you could express a predicate that "feels" like the following, in SQL: WHERE Var1 OR Var2 IN (1, 2, 3) /u/CyBerg90 has, on reddit. The idea was to create a predicate that yields true whenever both values Var1 and Var2 yield either 1, 2, or 3. The canonical solution The … Continue reading INTERSECT – the Underestimated Two-Way IN Predicate

ID Lists Aren’t the Best Solution for the N+1 Problem

In their eternal attempts to circumvent the N+1 problem, Hibernate users often resort to IN predicates with ID lists. In this post, we'll see how those users might just be replacing a horrible thing with a bad one, which is better but not yet good. Here's why: The N+1 Problem The N+1 problem is a … Continue reading ID Lists Aren’t the Best Solution for the N+1 Problem

SQL incompatibilities: NOT IN and NULL values

This is something where many hours of debugging have been spent in the lives of many SQL developers. The various situations where you can have NULL values in NOT IN predicates and anti-joins. Here's a typical situation: with data as ( select 1 as id from dual union all select 2 as id from dual … Continue reading SQL incompatibilities: NOT IN and NULL values