A very common misconception I often encounter with SQL users is the idea that DISTINCT is something like a function, and that it can take parenthesised arguments. Just recently, I've seen this Stack Overflow question where the OP was looking for a way to express this in jOOQ: SELECT DISTINCT (emp.id), emp.fname, emp.name FROM employee … Continue reading SQL DISTINCT is not a function
Tag: DISTINCT
How SQL DISTINCT and ORDER BY are Related
One of the things that confuse SQL users all the time is how DISTINCT and ORDER BY are related in a SQL query. The Basics Running some queries against the Sakila database, most people quickly understand: SELECT DISTINCT length FROM film This returns results in an arbitrary order, because the database can (and might apply … Continue reading How SQL DISTINCT and ORDER BY are Related
Counting Distinct Records in SQL
The SQL language and its depths... Some of you readers might be aware of MySQL's capability of counting distinct records through the COUNT() aggregate function. The MySQL documentation reads: COUNT(DISTINCT expr,[expr...]) Returns a count of the number of rows with different non-NULL expr values. In other words, you can count distinct first and last names very easily: SELECT … Continue reading Counting Distinct Records in SQL
The IS DISTINCT FROM predicate
The SQL-1999 standard specifies a useful IS DISTINCT FROM predicate, that behaves slightly different from the regular not equal comparison predicate. Here is its simple definition: 8.13 <distinct predicate> Format <distinct predicate> ::= <row value expression 3> IS DISTINCT FROM <row value expression 4> <row value expression 3> ::= <row value expression> <row value expression … Continue reading The IS DISTINCT FROM predicate