Plugin database tables in Wordpress - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to get the WordPress database global object.

Wordpress

<?php global [1]; ?>

Drag options to blanks, or click blank then click option'

A$post

B$plugin

C$user

D$wpdb

Attempts:

3 left

💡 Hint

Common Mistakes

Using $post instead of $wpdb

Forgetting the dollar sign

Using $plugin which is unrelated

The global variable $wpdb is used to interact with the WordPress database.

2fill in blank

medium

Complete the code to create a new table name with the WordPress prefix.

Wordpress

$table_name = [1] . 'my_plugin_table';

Drag options to blanks, or click blank then click option'

A$wpdb->name

B$wpdb->suffix

C$wpdb->prefix

D$wpdb->table

Attempts:

3 left

💡 Hint

Common Mistakes

Using $wpdb->suffix which does not exist

Using $wpdb->name which is not the prefix

Using $wpdb->table which is invalid

The $wpdb->prefix property holds the WordPress table prefix, which is used to create custom plugin tables.

3fill in blank

hard

Fix the error in the SQL query to create a table with the correct charset collate.

Wordpress

$charset_collate = [1];
$sql = "CREATE TABLE $table_name (
  id mediumint(9) NOT NULL AUTO_INCREMENT,
  name varchar(255) NOT NULL,
  PRIMARY KEY  (id)
) $charset_collate;";

Drag options to blanks, or click blank then click option'

A$wpdb->charset . ' COLLATE ' . $wpdb->collate

B$wpdb->charset . ' COLLATE=' . $wpdb->collate

C$wpdb->charset . ' ' . $wpdb->collate

D$wpdb->charset . ' COLLATE' . $wpdb->collate

Attempts:

3 left

💡 Hint

Common Mistakes

Missing spaces around 'COLLATE'

Using '=' sign incorrectly

Concatenating without spaces

The correct way to set charset and collation is to concatenate $wpdb->charset with ' COLLATE ' and $wpdb->collate.

4fill in blank

hard

Fill both blanks to prepare and execute a safe SQL query to insert data into the plugin table.

Wordpress

$wpdb->[1](
  $table_name,
  array('name' => $name),
  array([2] => '%s')
);

Drag options to blanks, or click blank then click option'

Ainsert

Bname

Cformat

Dupdate

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'update' instead of 'insert'

Using 'name' instead of 'format' for the third argument

Omitting the format array

Use insert method to add data and format to specify data types for safe queries.

5fill in blank

hard

Fill all three blanks to safely prepare and run a SQL query to get rows where name matches a variable.

Wordpress

$prepared_query = $wpdb->[1](
  "SELECT * FROM $table_name WHERE name = [2]",
  [3]
);
$results = $wpdb->get_results($prepared_query);

Drag options to blanks, or click blank then click option'

Aprepare

B'%s'

C$name

D$wpdb->prefix

Attempts:

3 left

💡 Hint

Common Mistakes

Not using prepare method

Using wrong placeholder like %d for strings

Passing wrong variable or prefix instead of $name

Use prepare to safely insert variables into SQL. Use '%s' as placeholder for strings and pass the variable $name.

Practice

1. Why do WordPress plugins create their own database tables instead of using existing WordPress tables?

easy

A. To avoid using any database at all

B. Because WordPress does not allow plugins to use existing tables

C. To keep plugin data separate and organized for better performance

D. To make the plugin load slower intentionally

Solution

1. Step 1: Understand plugin data management

   Plugins create their own tables to store data separately from WordPress core data.

2. Step 2: Benefits of separate tables

   This separation helps organize data and improves performance by avoiding clutter in core tables.

3. Final Answer:

   To keep plugin data separate and organized for better performance -> Option C

4. Quick Check:

   Separate tables improve organization and performance [OK]

Hint: Separate plugin data for better organization and speed [OK]

Common Mistakes:

• Thinking WordPress forbids using core tables
• Believing plugins avoid databases entirely
• Assuming slower load is intentional

2. Which of the following is the correct way to get the table name with the WordPress prefix for a plugin table named myplugin_data?

easy

A. $wpdb->prefix . 'myplugin_data'

B. $wpdb->myplugin_data

C. myplugin_data

D. $wpdb->prefix('myplugin_data')

Solution

1. Step 1: Understand $wpdb prefix usage

   $wpdb->prefix contains the WordPress table prefix, usually 'wp_'.

2. Step 2: Correct concatenation for table name

   Concatenate $wpdb->prefix with the table name string to get the full table name.

3. Final Answer:

   $wpdb->prefix . 'myplugin_data' -> Option A

4. Quick Check:

   Prefix plus table name string = correct table name [OK]

Hint: Use $wpdb->prefix . 'table_name' for plugin tables [OK]

Common Mistakes:

• Using $wpdb->myplugin_data directly
• Not adding prefix to table name
• Calling $wpdb->prefix as a function

3. Given this code snippet in a plugin activation hook:

$table_name = $wpdb->prefix . 'myplugin_data';
$sql = "CREATE TABLE $table_name (
  id mediumint(9) NOT NULL AUTO_INCREMENT,
  name varchar(100) NOT NULL,
  PRIMARY KEY  (id)
);";
dbDelta($sql);

What will happen when this code runs?

medium

A. It updates existing rows in the table

B. It creates the table with columns id and name if it doesn't exist

C. It causes a syntax error because dbDelta cannot create tables

D. It deletes the table if it exists

Solution

1. Step 1: Understand dbDelta function

   dbDelta safely creates or updates database tables based on the SQL CREATE statement.

2. Step 2: Analyze the SQL statement

   The SQL creates a table with id and name columns and a primary key on id.

3. Final Answer:

   It creates the table with columns id and name if it doesn't exist -> Option B

4. Quick Check:

   dbDelta creates or updates tables safely [OK]

Hint: dbDelta creates or updates tables from SQL CREATE statements [OK]

Common Mistakes:

• Thinking dbDelta deletes tables
• Assuming dbDelta causes syntax errors
• Confusing dbDelta with data update functions

4. A plugin developer wrote this code to create a table:

$table_name = $wpdb->prefix . 'myplugin_data';
$sql = "CREATE TABLE $table_name (
  id int NOT NULL AUTO_INCREMENT,
  name varchar(100) NOT NULL,
  PRIMARY KEY (id)
)";
dbDelta($sql);

But the table is not created after activation. What is the likely problem?

medium

A. dbDelta requires the SQL string to end with a semicolon

B. Missing semicolon at the end of the SQL statement

C. Not calling $wpdb->query() before dbDelta()

D. Using int instead of mediumint for id

Solution

1. Step 1: Check SQL syntax for dbDelta

   dbDelta requires the SQL CREATE statement to end with a semicolon to parse correctly.

2. Step 2: Identify missing semicolon

   The SQL string lacks a semicolon after the closing parenthesis, causing dbDelta to fail creating the table.

3. Final Answer:

   dbDelta requires the SQL string to end with a semicolon -> Option A

4. Quick Check:

   SQL must end with semicolon for dbDelta [OK]

Hint: Always end SQL string with semicolon for dbDelta [OK]

Common Mistakes:

• Ignoring semicolon requirement
• Thinking int vs mediumint causes failure
• Calling $wpdb->query() unnecessarily

5. You want to add a new column email varchar(255) NOT NULL to your plugin's custom table myplugin_data during an update. Which approach correctly updates the table without losing data?

hard

A. Ignore the database and store emails in a separate file

B. Drop the table and recreate it with the new column

C. Use $wpdb->query() to run ALTER TABLE and then run dbDelta() with old SQL

D. Modify the original CREATE TABLE SQL to include the new column and run dbDelta() again

Solution

1. Step 1: Understand dbDelta update behavior

   dbDelta compares the current table structure with the SQL and adds missing columns safely.

2. Step 2: Update CREATE TABLE SQL with new column

   Modify the SQL to include the new email column and run dbDelta() to update the table without data loss.

3. Final Answer:

   Modify the original CREATE TABLE SQL to include the new column and run dbDelta() again -> Option D

4. Quick Check:

   dbDelta updates tables by comparing SQL definitions [OK]

Hint: Update CREATE TABLE SQL and rerun dbDelta to add columns [OK]

Common Mistakes:

• Dropping table loses all data
• Running ALTER TABLE manually then old dbDelta
• Avoiding database updates by using files