SUBSTR and INSTR SQL Oracle

Question

I\'ve started using SUBSTR and INSTR in Oracle but I got confused when I came across this.

SELECT PHONE, SUBSTR(PHONE, 1, INSTR(PHONE, \'-\') -1)
FROM DIRECTORY;         


        

Answer 1

INSTR(PHONE, '-') gives the index of - in the PHONE column, in your case 4
and then SUBSTR(PHONE, 1, 4 - 1) or SUBSTR(PHONE, 1, 3)
gives the substring of the PHONE column from the 1st that has length of 3 chars which is 362,
if the value PHONE column is 362-127-4285.