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  • Remember: Don’t mix = and NULL

    I was recently performing an analysis on the database for my dissertation software, and wanted to look at one particular set of rows.  The table I was looking at is called Nodes, and because each node (represented by a row in the table) can optionally belong to a group, the group_id column allows for NULL…

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  • Book Review: The Undercover Economist Strikes Back

    In order to get an undergraduate degree from MIT, at least when I was there, you needed to take a certain number of humanities and social-science courses.  This was to stop you from coming out a complete one-dimensional student; the idea was that rounding out your education with knowledge from other fields was good for…

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  • Turning a PostgreSQL array to rows

    Bottom line: To turn a PostgreSQL array into rows, wrap the column in the UNNEST function: SELECT UNNEST(stuff) FROM foo. Each element of the array becomes its own row, which you can then join, filter, or feed into INTERSECT and UNION. Wrap the whole query in ARRAY(…) to pack the rows back into an array.…

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  • Turning PostgreSQL rows into arrays

    The short version: To turn a set of PostgreSQL rows into an array, wrap a subselect in the ARRAY function: SELECT ARRAY(SELECT description FROM Appointments). It returns one row with one array, holding one element per input row. Wrap that in array_to_string(…, ‘, ‘) to get a comma-separated string, and use AS to give the…

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  • Looking in PostgreSQL arrays with ANY

    So far, this series has looked at how to create PostgreSQL arrays, how to retrieve data from them, and how to get the length of an array’s outer and inner dimensions. But one of the most common actions that we’ll want to do with an array is look inside to see if a particular value…

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  • The real questions to ask offshore developers

    Friends of mine, who are not software developers, have a small, retail Internet business.  The original developers created the application in Python, and my friends are looking for a full-stack Web/Python developer to help them.  Frustrated with their inability to find someone who can commit to their project, my friends have decided to hire offshore developers, which…

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  • PostgreSQL array indexes and length

    In my last blog post, I introduced the idea of a PostgreSQL array, and showed how we can insert data into a table using either the curly-brace {} syntax, or the ARRAY construction syntax.  In this post, I want to talk about PostgreSQL indexes and length — what happens when we retrieve from indexes that exist (and…

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  • Learning to love PostgreSQL arrays

    I’ll admit it: When arrays were added to PostgreSQL a number of years ago, I thought that this was a really bad idea.  I’m a firm believer in normalization when it comes to database design and storage; and the idea of putting multiple values inside of a single column struck me as particularly foolish.  Besides,…

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  • Control-R, my favorite Unix shell command

    If you use a modern, open-source Unix shell — and by that, I basically mean either bash or zsh — then you really should know this shortcut.  Control-R is probably the shell command (or keystroke, to be technical about it) that I use most often, since it lets me search through my command history. Let’s…

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  • Starting a new software project? Don’t start coding right away.

    It’s always fun to start a new project. I should know; I’ve been a consultant since 1995, and have started hundreds of projects of various shapes and sizes.  It’s tempting, when I first meet a new client and come to an agreement, to dive right into the code, and start trying to solve their problems.…

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