SQL · Theory

VARCHAR

Theory

298/439

VARCHAR

VARCHAR(n) is variable-length text up to n characters (MySQL 8 utf8mb4: n is characters). name VARCHAR(50). CHAR(n) always uses n characters — rare now except fixed codes.

Don’t VARCHAR(255) everything without thought, but 255 is a common default. Too small = insert errors. TEXT is for long blobs (notes) — you cannot index TEXT the same way without a prefix.

Trap — VARCHAR for money or roll. Trap: CHAR(50) for names wasting space.

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

Exam tip

name VARCHAR(50) NOT NULL

VARCHAR — sample query

-- VARCHAR
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;

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

Short notes

DefVARCHAR(n) variable text up to n characters.
RuleNames VARCHAR. Long notes TEXT. Numbers INT.
TrapVARCHAR for roll/money.

SQL · Theory

VARCHAR

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Theory

298/439

VARCHAR

VARCHAR(n) is variable-length text up to n characters (MySQL 8 utf8mb4: n is characters). name VARCHAR(50). CHAR(n) always uses n characters — rare now except fixed codes.

Don’t VARCHAR(255) everything without thought, but 255 is a common default. Too small = insert errors. TEXT is for long blobs (notes) — you cannot index TEXT the same way without a prefix.

Trap — VARCHAR for money or roll. Trap: CHAR(50) for names wasting space.

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

Exam tip

name VARCHAR(50) NOT NULL

VARCHAR — sample query

-- VARCHAR
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;

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

Short notes

DefVARCHAR(n) variable text up to n characters.
RuleNames VARCHAR. Long notes TEXT. Numbers INT.
TrapVARCHAR for roll/money.

VARCHAR

VARCHAR — sample query

Short notes

Questions

VARCHAR

VARCHAR — sample query

Short notes

Questions