A date from a CSV file lands as text in the database — and suddenly the 2nd of November turns into the 11th of February. These silent misinterpretations are the classic pitfall of type conversion in SQL Server. Anyone who knows CAST, CONVERT, TRY_CAST and TRY_CONVERT together with the style parameter avoids them. The essentials up front: Prerequisite: SQL Server with SSMS; … Read more
A data migration from SQL Server to PostgreSQL rarely fails at actually copying the data. It fails at the silent differences that only surface in the target: datetime, which knows no time zone, bit, which is not a boolean, an IDENTITY that turns into a sequence, and a collation that suddenly compares case-sensitively. Anyone who sets out to migrate SQL Server to PostgreSQL isn’t … Read more
The row counts match — table by table, source against target, all green. And yet the migration isn’t finished. In one column, NULL values have turned into empty strings; in another, the detour through a CSV file rounded the last decimal of an amount; and a handful of accented characters collapsed into question marks. Same count is not … Read more
The data is over, the schema stands — and then there are 200 stored procedures sitting there that no tool translates for you. pgloader migrates tables and data, but the logic in procedures, functions, and triggers stays behind. This is the phase that’s actually work: porting T-SQL to PL/pgSQL, line by line, with understanding instead of search-and-replace. The … Read more
Moving data sounds like the easiest phase of a migration: the table is there, pour the data in, done. Until the first larger table takes a whole afternoon — because it runs row by row via INSERT instead of in one sweep via COPY. Anyone who needs to load data into PostgreSQL has four routes to choose from, and the … Read more
A SQL Server to PostgreSQL schema migration looks finished the moment the CREATE TABLE script runs without an error. That is exactly when the real trouble begins: the table is there, the data is loaded — and the first INSERT that should hand out a new ID collides with an existing key. The reason is not a typo but a change … Read more
A view is the most elegant way to encapsulate a recurring query — right up to the moment the query needs an argument from outside. A view has no parameters. As soon as a value belongs in the WHERE that the caller supplies, the table-valued function is the tool of choice: a function that returns an entire result set … Read more
A migration from SQL Server to PostgreSQL rarely fails at actually copying the data. It fails at datetime, where the choice between timestamp and timestamptz is anything but cosmetic, at bit, which is not a boolean, and at money, which you’d be better off not touching in PostgreSQL at all. The SQL Server to PostgreSQL data type mapping decides whether the data arrives cleanly — … Read more
Bad data gives no warning. An age of 200 years, a duplicate customer number, a country code that doesn’t exist — in the source system nobody notices. Only when the ETL run tries to push the rows into the strictly modelled target layer does the load break: on a CHECK, on a UNIQUE index, on a foreign key. Checking … Read more
“We do ETL.” You hear it in almost every data team — and it is often wrong. If every transformation runs as a stored procedure after the raw data has already been loaded, unchanged, into a staging table, then what you have is really ELT. The label hides what is actually happening. The difference between ETL vs. ELT is … Read more
