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University · Data systems

Which clause specifies result ordering in an ordinary SQL query?

  1. ORDER BY
  2. SELECT alone always
  3. WHERE alone
  4. The table filename
Answer and explanation

ORDER BY

Without explicit ordering, result order should not be assumed.

University · Data systems

A table contains 12 rows and a stated filter matches 5. How many rows does SELECT without grouping return for that filter?

Answer and explanation

5

The filter retains exactly the five matching rows.

University · Data systems

What is a primary key intended to do?

  1. Uniquely identify rows under its constraint
  2. Make every column secret
  3. Sort every query automatically
  4. Guarantee that all text is accurate
Answer and explanation

Uniquely identify rows under its constraint

Uniqueness and non-null key constraints identify records, not all semantic truth.

University · Data systems

Why can joining a parent table to several matching child records repeat the parent values?

Answer and explanation

Each matching parent-child combination appears in the join result. A one-to-many relation naturally produces multiple rows.

Credit join cardinality.

University · Data systems

Why use parameterized SQL for user-supplied values?

  1. Remove all need for permissions
  2. Make every query return one row
  3. Keep values separate from executable SQL syntax
  4. Automatically correct every schema
Answer and explanation

Keep values separate from executable SQL syntax

Parameter binding reduces injection risk from data values.

University · Data systems

Three parent rows each match two child rows under the stated join. How many joined rows result?

Answer and explanation

6

3×2=6 combinations.

Study notes

Relational data, SQL and safe queries

A relational table holds rows and columns with a defined schema. Keys identify rows or relationships, while constraints enforce some consistency rules.

University

Ideal payload transfer time

Assume no protocol overhead or contention. MB and Mbps use decimal prefixes, not binary mebibytes.

Grades 9–12

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