[GENERAL] Check constraint problem

[Michael Schmidt]

New to PostgreSQL and hoping for some help with a constraint I've been struggling with for a could of days.  The table includes means and standard deviations.  They should either both be null or (mean any value and standard deviation >= 0)   The constraint statement:   ALTER TABLE "ClinData" ADD CONSTRAINT "Control_Score" CHECK ((("Control_Score_M" IS NULL) AND ("Control_Score_SD" IS NULL) ) OR (("Control_Score_M" IS NOT NULL) AND ("Control_Score_SD" >= 0.0)))   This statement executes okay.  It prevents Control_Score_M of NULL and Control_Score_SD = 1.0 (as it should).  However, it allows Control_Score_M = 1 and Control_Score_SD of NULL (it shouldn't).  Any thoughts about what is wrong.  Thanks!   Michael Schmidt