SQL · Theory

LPAD()()

Theory

151/439

LPAD()()

LPAD() pad on the left to a length. You use it in SELECT (and sometimes WHERE/UPDATE). It does not change stored data unless you UPDATE … SET col = LPAD(col).

Board: SELECT LPAD(roll, 3, '0') 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). Truncates if the string is already longer.

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

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

Exam tip

Say what LPAD returns, then SELECT LPAD(roll, 3, '0') FROM students;

LPAD()() — sample query

-- LPAD()()
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;

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

Short notes

DefLPAD() pad on the left to a length.
RuleSELECT LPAD(roll, 3, '0') FROM students;
TrapTruncates if the string is already longer.

SQL · Theory

LPAD()()

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Theory

151/439

LPAD()()

LPAD() pad on the left to a length. You use it in SELECT (and sometimes WHERE/UPDATE). It does not change stored data unless you UPDATE … SET col = LPAD(col).

Board: SELECT LPAD(roll, 3, '0') 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). Truncates if the string is already longer.

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

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

Exam tip

Say what LPAD returns, then SELECT LPAD(roll, 3, '0') FROM students;

LPAD()() — sample query

-- LPAD()()
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;

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

Short notes

DefLPAD() pad on the left to a length.
RuleSELECT LPAD(roll, 3, '0') FROM students;
TrapTruncates if the string is already longer.

LPAD()()

LPAD()() — sample query

Short notes

Questions

LPAD()()

LPAD()() — sample query

Short notes

Questions