SQL · Theory

CHARACTER_LENGTH()()

Theory

134/439

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.

Exam tip

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

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.

Short notes

DefCHARACTER_LENGTH() same idea as CHAR_LENGTH — count characters.
RuleSELECT CHARACTER_LENGTH(name) FROM students;
TrapLENGTH is bytes.

SQL · Theory

CHARACTER_LENGTH()()

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Theory

134/439

CHARACTER_LENGTH()()

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.

Exam tip

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

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.

Short notes

DefCHARACTER_LENGTH() same idea as CHAR_LENGTH — count characters.
RuleSELECT CHARACTER_LENGTH(name) FROM students;
TrapLENGTH is bytes.

CHARACTER_LENGTH()()

CHARACTER_LENGTH()() — sample query

Short notes

Questions

CHARACTER_LENGTH()()

CHARACTER_LENGTH()() — sample query

Short notes

Questions