MySQL Drop Index

MySQL DROP INDEX Statement Syntax

The syntax for dropping an index in MySQL is:

Here, table_name is the name of the table from which you want to drop an index, and index_name is the name of the index that you want to drop. This statement tells MySQL to remove the index from the specified table.

MySQL DROP INDEX Algorithm Option

The Algorithm option is used to specify the ALGORITHM option in order to control the algorithm used for dropping the index. The two options are:

• COPY (default): The COPY algorithm creates a temporary table to hold the data from the original table. It then drops the index from the original table and copies the data back from the temporary table. This algorithm can be slower but safer, as it ensures data integrity during the operation.
• INPLACE: The INPLACE algorithm drops the index without creating a temporary table. This algorithm can be faster but may not guarantee data integrity, so it's not recommended for large tables or critical data.

The syntax for dropping an index using the Algorithm option is:

MySQL DROP INDEX Lock Option

The Lock option is used to specify the lock type that MySQL should use when dropping the index. The four options are:

• DEFAULT (default): The DEFAULT lock type is the default option, and it chooses the appropriate lock type based on the algorithm used.
• NONE: The NONE lock type does not acquire a lock, which can be useful for read-only operations.
• SHARED: The SHARED lock type acquires a shared lock, which allows other sessions to read the table but not modifies it.
• EXCLUSIVE: The EXCLUSIVE lock type acquires an exclusive lock, which prevents other sessions from accessing the table during the operation.

The syntax for dropping an index using the Lock option is:

MySQL DROP INDEX Statement Examples

Here are some examples of how to drop an index in MySQL with the syntax, algorithm, and lock options.

Example: Example Using Algorithm and Lock

The Below example creates a table named "MyTable" with a single column "value" of integer data type. The script then inserts five rows of data into the "value" column of the "MyTable" table.

Next, the script creates an index called "sample_index" on the "value" column of the "MyTable" table using the BTREE algorithm. The script then prints out the list of indexes on the "MyTable" table using the "SHOW INDEXES" statement. This will show information about the created index including its name, type, and the columns it is based on.

Finally, the script drops the "sample_index" index from the "MyTable" table using the "DROP INDEX" statement with the "ALGORITHM=COPY" and "LOCK=SHARED" options. The "COPY" algorithm means that a new copy of the table will be created with the index removed and then renamed to replace the original table, which can be slower and more resource-intensive than the "INPLACE" algorithm used in the previous code. The "LOCK=SHARED" option means that the index will be locked with a shared lock while it is being dropped, which will allow other transactions to read from the table but not modify it until the drop operation is completed.

Output:

The "DROP INDEX" command removes the "sample_index" index from the "MyTable" table using the "COPY" algorithm and a shared lock.

MySQL DROP PRIMARY KEY Index

To drop the primary key index in MySQL, you can use the following syntax:

This statement drops the primary key index from the specified table. The primary key is a special type of index that uniquely identifies each row in the table. You can drop it using the DROP PRIMARY KEY clause, which tells MySQL to remove the primary key from the table.

Example: MySQL DROP PRIMARY KEY Index

The code creates a table MyTable with columns pk and value. pk is the primary key. Data is inserted into the table. An index sample_index is created on the value column. Information about the indexes defined on MyTable is printed. Finally, the primary key index is dropped from the table.

Output:

MCQs

1. What is the syntax for dropping an index in MySQL?
   • A) ALTER TABLE table_name REMOVE INDEX index_name;
   • B) ALTER TABLE table_name DROP INDEX index_name;
   • C) ALTER INDEX table_name DROP index_name;
   • D) ALTER INDEX table_name REMOVE index_name;

Correct Answer: B

2. What is the purpose of the Algorithm option when dropping an index in MySQL?
   • A) To specify the index name.
   • B) To specify the lock type.
   • C) To specify the algorithm for dropping the index.
   • D) To specify the table name.

Correct Answer: C

3. Which lock type acquires a shared lock when dropping an index in MySQL?
   • A) DEFAULT
   • B) NONE
   • C) SHARED
   • D) EXCLUSIVE

Correct Answer: C