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
Tag: sql-1999
Row value expressions and the BETWEEN predicate
Now this is a simple example of how SQL clause simulation can get nasty if you want to make use of some more advanced SQL clauses that aren't supported in all databases. Consider the following predicate and equivalent transformations thereof: The BETWEEN predicate The BETWEEN predicate is a convenient form of expressing the fact that … Continue reading Row value expressions and the BETWEEN predicate
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