SQL · Theory

Not Equal

Theory

55/439

Not Equal

Not equal is <> or != . WHERE marks <> 0; MySQL accepts both. Standard SQL prefers <>. NULL <> 0 is not true — use IS NOT NULL as well if you need rows with a value that is not 0.

Trap — marks != NULL. Use IS NOT NULL.

On the example next to this theory: Not Equal: create two demo rows, then SELECT qty >= 2 ordered. Say which labels come back.

Exam tip

WHERE marks <> 40; never != NULL.

Not Equal — sample query

-- Not Equal
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;

Not Equal: create two demo rows, then SELECT qty >= 2 ordered. Say which labels come back.

Short notes

Def<> or != means not equal.
RulePrefer <>. Combine with IS NOT NULL when needed.
Trap!= NULL.

SQL · Theory

Not Equal

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Theory

55/439

Not Equal

Not equal is <> or != . WHERE marks <> 0; MySQL accepts both. Standard SQL prefers <>. NULL <> 0 is not true — use IS NOT NULL as well if you need rows with a value that is not 0.

Trap — marks != NULL. Use IS NOT NULL.

On the example next to this theory: Not Equal: create two demo rows, then SELECT qty >= 2 ordered. Say which labels come back.

Exam tip

WHERE marks <> 40; never != NULL.

Not Equal — sample query

-- Not Equal
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;

Not Equal: create two demo rows, then SELECT qty >= 2 ordered. Say which labels come back.

Short notes

Def<> or != means not equal.
RulePrefer <>. Combine with IS NOT NULL when needed.
Trap!= NULL.

Not Equal

Not Equal — sample query

Short notes

Questions

Not Equal

Not Equal — sample query

Short notes

Questions