SQL Lesson 14: Updating rows

In addition to adding new data, a common task is to update existing data, which can be done using an UPDATE statement. Similar to the INSERT statement, you have to specify exactly which table, columns, and rows to update. In addition, the data you are updating has to match the data type of the columns in the table schema.

Update statement with values
UPDATE mytable SET column = value_or_expr, other_column = another_value_or_expr, … WHERE condition;

The statement works by taking multiple column/value pairs, and applying those changes to each and every row that satisfies the constraint in the WHERE clause.

Taking care

Most people working with SQL will make mistakes updating data at one point or another. Whether it's updating the wrong set of rows in a production database, or accidentally leaving out the WHERE clause (which causes the update to apply to all rows), you need to be extra careful when constructing UPDATE statements.

One helpful tip is to always write the constraint first and test it in a SELECT query to make sure you are updating the right rows, and only then writing the column/value pairs to update.

Exercise

It looks like some of the information in our Movies database might be incorrect, so go ahead and fix them through the exercises below.

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Table: movies
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Exercise 14 — Tasks
  1. The director for A Bug's Life is incorrect, it was actually directed by John Lasseter
  2. The year that Toy Story 2 was released is incorrect, it was actually released in 1999
  3. Both the title and directory for Toy Story 8 is incorrect! The title should be "Toy Story 3" and it was directed by Lee Unkrich
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Solve all tasks to continue to the next lesson.
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