is never contained in the Number column, the result of the expression (and therefore your program flow) may still vary over time according to the absence or presence of NULLs in the column. Hours of already seen examples of NULL being returned where you would expect true, and that does affect the flow of the code! Below are some examples of the seemingly paradoxical (but perfectly correct) results

block that delineates the procedure’s PSQL code. Within that block could be PSQL and DML statements, flow-of-control blocks, sequences of other BEGIN…END blocks, including embedded blocks. Blocks, including