SQL · Theory

LENGTH()()

Theory

146/439

LENGTH()()

LENGTH() length in bytes (not always characters for utf8mb4). You use it in SELECT (and sometimes WHERE/UPDATE). It does not change stored data unless you UPDATE … SET col = LENGTH(col).

Board: SELECT name, 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). CHAR_LENGTH is characters; LENGTH is bytes.

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

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

Exam tip

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

LENGTH()() — sample query

-- 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;

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

Short notes

DefLENGTH() length in bytes (not always characters for utf8mb4).
RuleSELECT name, LENGTH(name) FROM students;
TrapCHAR_LENGTH is characters; LENGTH is bytes.

SQL · Theory

LENGTH()()

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Theory

146/439

LENGTH()()

LENGTH() length in bytes (not always characters for utf8mb4). You use it in SELECT (and sometimes WHERE/UPDATE). It does not change stored data unless you UPDATE … SET col = LENGTH(col).

Board: SELECT name, 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). CHAR_LENGTH is characters; LENGTH is bytes.

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

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

Exam tip

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

LENGTH()() — sample query

-- 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;

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

Short notes

DefLENGTH() length in bytes (not always characters for utf8mb4).
RuleSELECT name, LENGTH(name) FROM students;
TrapCHAR_LENGTH is characters; LENGTH is bytes.

LENGTH()()

LENGTH()() — sample query

Short notes

Questions

LENGTH()()

LENGTH()() — sample query

Short notes

Questions