Cursed Knowledge

Cursed knowledge the Ibis developers have acquired via battling with many, many execution engines.

Oracle

• Oracle’s LTRIM and RTRIM functions accept a set of whitespace (or other) characters to remove from the left-, and right-hand-side sides of the input string, but the TRIM function only accepts a single character to remove.

Impala

• Impala’s LTRIM and RTRIM functions accept a set of whitespace (or other) characters to remove from the left-, and right-hand-side sides of the input string, but the TRIM function only removes spaces.

ClickHouse

• ClickHouse’s random number generating functions are considered in common subexpression elimination, so to get two unique random numbers, users must defeat that optimization. This is done by passing any argument to those functions. It’s left as an exercise for the reader to figure out how to generate two unique inputs.