Structured query language (SQL): FROM

The idea

FROM is the clause that names the table a query searches. In AQA GCSE Computer Science SQL, the pattern is SELECT fields FROM table, optionally followed by WHERE conditions. FROM does not choose which columns appear (SELECT does) and does not filter rows (WHERE does); it simply states the source table, such as FROM Students. A query can only read fields that exist in the named table, so the table after FROM must match the fields listed after SELECT. When answering multiple-choice questions, link FROM to the data source and keep it distinct from the other keywords so each part of the query is understood separately.

What earns the marks

• Identifies FROM as the clause that specifies the table being queried.
• Recognises that the table name follows FROM in a SELECT statement.
• Distinguishes FROM (source table) from SELECT (output fields) and WHERE (row filter).
• Accepts that fields named after SELECT must belong to the table named after FROM.

Common mistakes and how to put them right

• Thinking FROM lists the fields to return.

  Put it right: Fields follow SELECT; FROM names the table.

• Believing FROM applies conditions to rows.

  Put it right: Conditions are set by WHERE; FROM only identifies the source table.

• Assuming FROM can name several unrelated tables freely.

  Put it right: In GCSE queries FROM names the single table the fields come from.

Exam tips

• Match each keyword to one job: SELECT fields, FROM table, WHERE condition.
• Check that every field after SELECT exists in the table named after FROM.
• When asked what a query searches, look at the word immediately after FROM.