The SQL NULL is the term used to represent a missing value. A NULL value in a table is a value in a field that appears to be blank. A field with a NULL value is a field with no value. It is very important to understand that a NULL value is different than a zero value or a field that contains spaces.
Median rhomboid glossitis is a condition that can affect your tongue if you have oral thrush. It causes a red, smooth patch or lump to develop in the middle of the top part of your tongue, which can be sore. You're more likely to develop oral thrush if you: have recently taken antibiotics.
Some other causes of coated white tongue are accumulation of keratin or dead skin cells on the surface of tongue, tobacco abuse, consumption of extremely hot foods or beverages etc. Abnormal buildup of keratin is generally caused by dehydration as it tends to dry out saliva, thereby making the tongue dry.