Be able to use SQL to edit and delete data in a database using the commands.

The idea

SQL is the language used to work with relational databases. Editing means changing values already stored in existing records, which is done with UPDATE ... SET ... WHERE. Deleting means removing whole records (rows) from a table, which is done with DELETE FROM ... WHERE. Both commands act on the rows that satisfy the WHERE condition, so the condition is the safety catch: without it, UPDATE changes every row and DELETE empties the table. For example, in a table Student with columns StudentID, Name and Year, the statement UPDATE Student SET Year = 11 WHERE StudentID = 42 changes one learner's year group, while DELETE FROM Student WHERE StudentID = 42 removes that one record. Neither command changes the table's structure; adding or removing columns is a different job.

What earns the marks

• UPDATE is the command that edits existing data values in a table; it does not create new records or new tables.
• SET lists the column or columns being changed and the new value for each, for example SET Year = 11.
• DELETE FROM removes whole records (rows) from a named table rather than blanking individual field values.
• A WHERE clause restricts which rows are affected; omitting it means every row in the table is edited or deleted.
• Choosing the correct command for the task: changing a stored value uses UPDATE, removing a record uses DELETE.
• The table name follows the command (UPDATE table_name / DELETE FROM table_name) and identifies which table is affected.

Common mistakes and how to put them right

• Using UPDATE to remove a record.

  Put it right: UPDATE changes values in existing rows, whereas removing a record needs DELETE FROM with a WHERE condition.

• Leaving out the WHERE clause.

  Put it right: This edits or deletes every row in the table, so always state the condition that identifies the intended record.

• Confusing DELETE with removing a column or the whole table.

  Put it right: DELETE FROM removes rows of data, not the table's structure.

• Writing SET before naming the table, or placing WHERE before SET.

  Put it right: The order is command, table name, SET assignments, then WHERE condition.

Exam tips

• Read the scenario and decide first whether a value is being changed (UPDATE) or a record is being removed (DELETE), then write the command.
• Always include a WHERE clause that pins down the single record or group of records named in the question.
• Check the column names and table name against any table given in the question and copy them exactly.
• For a multiple-choice question, eliminate options that omit WHERE or that use the wrong command for the task described.