Sql

Dynamic SQL without stored procedures

Sometimes it’s necessary to run dynamic SQL, but it’s not always possible (or sensible) to write a stored procedure just for that.

Postgres and Oracle both support functions that can run queries using dynamic SQL and return the result of those queries as XML.

PIVOT Alternatives

One type of problems is inherently complicated with SQL: turning rows into columns. This is very often referred to as a “crosstab” or “pivot”.

GROUP BY vs DISTINCT

Every now and then I see queries that use GROUP BY without any aggregates which is the same as using DISTINCT instead.

Unpivot with Postgres

Sometimes it’s necessary to normalize de-normalized tables - the opposite of a “crosstab” or “pivot” operation. Postgres does not support the standard UNPIVOT operator, but simulating it is very simple.

Performance of stored functions

Something that users coming from other database systems easily overlook is, that Postgres supports different languages for writing stored functions (and procedures). Choosing the right language can influence the performance of your functions.