The SUBSTR function is used to extract characters from a word or sentence.

For Example, I have run into many situations were I need to apply different programming logic based on characters in a string.

Suppose I have an employee table with an employee_id and employee_name (First, Last, middle) and I want to store the middle name in my database as middle initial only. So I only need the first character of the middle name.

I can simply do this by using a SUBSTR on the middle name field.

The first argument in the example above for the SUBSTR function is the column name. The second argument is a number which is the starting position of where you want to grab the character from; In this example I want the first character so I use 0 or you can use 1). The last argument is how many characters you want to grab from the string, in this case I want only 1 character so I said 1.