Visualizing missing data in databases

Missing data in databases can cause bugs in applications or incorrect calculations. Recently, while working on a RETS application, I needed to ensure that not many missing values were encountered in one of the MySQL tables. Although one could easily write a SQL query to find the percentage of missing values, I many times find it easier to first get a visual representation of the amount of missing data there is in the table, and then drill-down further if required. One library that I found that lets you easily get a visual representation of missing data in your database tables is missingno – a Python library.
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Combinatorial row pairing in databases

While working on a database design I came across the problem of finding combinations or ‘cartesian product’ between all the rows between one table to another table, but not repeating the same permutations.

Take the ‘Teams’ table below which lists four cricket teams. We want to create a combination list of matches between each teams.
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