10 articles tagged #Data Engineering
Your pandas.merge() operation suddenly doubles or triples the number of rows, even though the merge completes successfully. The cause is usually non-unique join keys that produce many-to-many relationships. Learn why duplicate rows appear after merges and how to validate, diagnose, and fix them
Pandas groupby() is one of the most powerful tools for data aggregation, but subtle issues such as missing values, duplicate keys, incorrect aggregation functions, or dropped categories can silently produce incomplete results. Learn how to identify and prevent silent data loss in your groupby
If pandas.read_sql() is returning outdated, incomplete, or unexpected results, the problem often isn't Pandas itself. Database transactions, connection pooling, replicas, query caching, and isolation levels can all affect what your application reads. Learn how to identify and resolve the most common
PostgreSQL's COPY FROM can silently drop rows when your null string or delimiter doesn't match the file exactly — no error, no warning, just missing data. Here's how to diagnose and fix it for good.
Bulk inserts combined with PostgreSQL's ON CONFLICT DO NOTHING can dramatically improve performance and simplify deduplication. However, many developers are surprised when rows silently disappear during large imports. Learn why missing rows occur, how SQLAlchemy handles conflicts, and how to safely
xlsxwriter silently drops or corrupts hyperlinks when the display text exceeds 255 characters. Learn exactly why this limit exists, how to detect it, and three practical workarounds you can ship today.
Merging multiple sheets into one with xlsxwriter and ending up with headers sprinkled throughout your data? Here's exactly why that happens and how to write the merge loop that gets it right every time.
Your read_csv call is crawling on a file that should load in seconds. Before you rewrite your pipeline, check these common culprits — dtype inference, unnecessary columns, and chunking strategy — in the right order.
Bulk-inserting rows into PostgreSQL and watching foreign key violations disappear without an error? This guide explains exactly why that happens and how to force PostgreSQL to catch every violation reliably.
You've enabled text_wrap in xlsxwriter but Excel still cuts off your long strings mid-sentence. The culprit is almost always row height — xlsxwriter doesn't auto-expand it for you. Here's how to fix it properly.