SQL · Theory

REVERSE()()

Theory

162/439

REVERSE()()

REVERSE() mirrors the text. You use it in SELECT (and sometimes WHERE/UPDATE). It does not change stored data unless you UPDATE … SET col = REVERSE(col).

Board: SELECT REVERSE(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). Interview toy — rare in production.

Interview — name REVERSE, one argument list, one example on the students table. Don’t recite every string function.

On the example next to this theory: REVERSE()(): create two demo rows, then SELECT qty >= 2 ordered. Say which labels come back.

Exam tip

Say what REVERSE returns, then SELECT REVERSE(name) FROM students;

REVERSE()() — sample query

-- REVERSE()()
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;

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

Short notes

DefREVERSE() mirrors the text.
RuleSELECT REVERSE(name) FROM students;
TrapInterview toy — rare in production.

SQL · Theory

REVERSE()()

← All stacks

Theory

162/439

REVERSE()()

REVERSE() mirrors the text. You use it in SELECT (and sometimes WHERE/UPDATE). It does not change stored data unless you UPDATE … SET col = REVERSE(col).

Board: SELECT REVERSE(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). Interview toy — rare in production.

Interview — name REVERSE, one argument list, one example on the students table. Don’t recite every string function.

On the example next to this theory: REVERSE()(): create two demo rows, then SELECT qty >= 2 ordered. Say which labels come back.

Exam tip

Say what REVERSE returns, then SELECT REVERSE(name) FROM students;

REVERSE()() — sample query

-- REVERSE()()
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;

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

Short notes

DefREVERSE() mirrors the text.
RuleSELECT REVERSE(name) FROM students;
TrapInterview toy — rare in production.

REVERSE()()

REVERSE()() — sample query

Short notes

Questions

REVERSE()()

REVERSE()() — sample query

Short notes

Questions