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Postgres Upserts

Since Postgres 9.5, Postgres has supported a useful a feature called UPSERT. For a reason I can’t figure out, this feature is referred to as UPSERT, even though there is no UPSERT SQL command. In addition to being … Read the rest

Posted on June 22, 2017April 20, 2019 by malisper 0

Postgres Transaction Isolation Levels

This post is part 3 in a three part series exploring transaction isolation issues in Postgres. Part 1 introduced some of the common problems that come up with transaction isolation in Postgres. Part 2 introduced row level locks, … Read the rest

Posted on June 21, 2017April 20, 2019 by malisper 1

Postgres Row Level Locks

This post is part 2 in a three part series exploring transaction isolation in Postgres. Part 1 introduced some of the problems that come up under the default isolation settings. This part and the next one introduce common ways … Read the rest

Posted on June 20, 2017April 20, 2019 by malisper 4

Postgres Transactions Aren’t Fully Isolated

This post is part 1 of a three part series examining transaction isolation in Postgres. This post covers the issues the come up under the default Postgres settings. Parts 2 and 3 will cover the different ways to eliminate the … Read the rest

Posted on June 19, 2017April 20, 2019 by malisper 12

Postgres Window Functions

Postgres window functions are an extremely useful feature. They let you calculate a value for each row based on the values of other rows. For our examples, let’s say we have a table ints full of random numbers:

The most … Read the rest

Posted on June 16, 2017December 21, 2017 by malisper 0

SELECT DISTINCT ON … ORDER BY

A common problem I’ve seen that many people are unfamiliar with how to solve is obtaining all of the rows that are the maximum of one value grouped by another value. For example, you may have a pets table with … Read the rest

Posted on June 15, 2017June 15, 2017 by malisper 0

The Missing Postgres Scan: The Loose Index Scan

Postgres has many different types of scans builtin. The list includes sequential scans, index scans, and bitmap scans. One useful scan type Postgres does not have builtin that other databases do is the loose index scan. Both MySQL … Read the rest

Posted on June 14, 2017April 20, 2019 by malisper 2

Postgres Lateral Joins

Personally, lateral joins are one of my favorite Postgres features. They are simple, while at the same time they let you write queries that would be nearly impossible to write otherwise. I find it surprising lateral joins were only introduced … Read the rest

Posted on June 13, 2017June 13, 2017 by malisper 7

Understanding Postgres Recursive CTEs

Unlike ordinary CTEs, which can be thought of as syntactic sugar, recursive CTEs make SQL a more powerful language. As the name suggests a recursive CTE makes it possible to express recursion in SQL. The ability to express recursion … Read the rest

Posted on June 12, 2017April 13, 2019 by malisper 0

Postgres CTEs

CTEs, also know as Common Table Expressions, are a way of refactoring a query. They let you give the result of a subquery a name and reuse the result multiple times. The general syntax of a CTE looks like the … Read the rest

Posted on June 9, 2017June 9, 2017 by malisper 0
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