CHARACTER_LENGTH()() — SQL Technical Interview Questions & Answers

CHARACTER_LENGTH()()

CHARACTER_LENGTH()()

  • CHARACTER_LENGTH() same idea as CHAR_LENGTH — count characters. You use it in SELECT (and sometimes WHERE/UPDATE). It does not change stored data unless you UPDATE … SET col = CHARACTER_LENGTH(col).
  • Board: SELECT CHARACTER_LENGTH(name) FROM students; Run it. Say the result out loud. If the column is NULL, the result is often NULL — wrap with IFNULL if you need a blank instead.
  • String indexes in MySQL start at 1, not 0 (SUBSTR, INSTR, LEFT). LENGTH is bytes.
  • Interview: name CHARACTER_LENGTH, one argument list, one example on the students table. Don’t recite every string function.
  • On the example next to this theory: CHARACTER_LENGTH()(): create two demo rows, then SELECT qty >= 2 ordered. Say which labels come back.

Technical Interview Tip: Say what CHARACTER_LENGTH returns, then SELECT CHARACTER_LENGTH(name) FROM students;

Code Examples for CHARACTER_LENGTH()()

CHARACTER_LENGTH()() — sample query

-- CHARACTER_LENGTH()()
CREATE TABLE demo (
  id INTEGER PRIMARY KEY,
  label TEXT NOT NULL,
  qty INTEGER DEFAULT 0
);
INSERT INTO demo (id, label, qty) VALUES
  (1, 'alpha', 2),
  (2, 'beta', 5);
SELECT label, qty FROM demo WHERE qty >= 2 ORDER BY qty DESC;

CHARACTER_LENGTH()(): create two demo rows, then SELECT qty >= 2 ordered. Say which labels come back.

How to Explain CHARACTER_LENGTH()() to an Interviewer

What does CHARACTER_LENGTH do?

same idea as CHAR_LENGTH — count characters SELECT CHARACTER_LENGTH(name) FROM students;

Does it UPDATE the table?

No, unless you write UPDATE SELECT only prints