Comparison operators are an important part of most programming languages.
Comparison operators are used to compare two expressions. The result is either true or false. It could also be unknown. This could also be represented by either 1, 0, or NULL, depending on the language. These are typically known as “Boolean expressions”.
When used with databases, comparison operators can be used inside your SQL queries to filter data to a certain criteria.
Continue readingYou can use the T-SQL EXCEPT operator in SQL Server to return distinct rows from the left input query that aren’t output by the right input query.
In SQL Server, you can use the T-SQL INTERSECT operator to return distinct rows that are output by both the left and right input queries.
In PostgreSQL, you can use the OVERLAPS operator to test for overlapping time periods.
The function returns true when two time periods (defined by their endpoints) overlap, and false when they do not overlap.
Continue readingIn SQL Server, the IIF() function (not to be confused with the IF statement) is a conditional function that returns the second or third argument based on the evaluation of the first argument.
It’s a shorthand way for writing a CASE expression. It’s logically equivalent to CASE WHEN X THEN Y ELSE Z END assuming IIF(X, Y, Z).
IIF() is an abbreviation for Immediate IF.
Most (probably all) programming languages include some form of the IF statement that allows programmers to write conditional code. That is, code that will execute only if a certain condition is true.
It’s a very simple concept. Basically it goes like this:
“If this, do that.”
Most languages simply call it IF, but some have their own twist on the name (for example, in ColdFusion/CFML, it’s called CFIF).
In any case, they essentially do the same thing.
In SQL Server (or more precisely, its programming language T-SQL) it’s called IF.
In PostgreSQL, you can use the AT TIME ZONE clause to convert a timestamp to another timezone.
In PostgreSQL, the make_interval() function creates an interval from years, months, weeks, days, hours, minutes and seconds fields.
You provide the years, months, weeks, days, hours, minutes and/or seconds fields, and it will return an interval in the interval data type.
Continue readingIn PostgreSQL, the make_timestamptz() function allows you to create a timestamp with time zone from its year, month, day, hour, minute and seconds fields, as well as an optional timezone field.
In PostgreSQL, the make_date() function allows you to create a date from its separate year, month and day fields.
Each date part is provided as an integer, and the result is returned as a date.
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