How Can I Reliably Check for and Create a Column in MySQL?

Verifying Column Existence in MySQL Tables

Determining the presence of a particular column in a MySQL table is a fundamental task in database programming. However, compared to other relational database systems, MySQL's approach to this query can be perplexing.

Consider the following query attempt, designed to both check for and create a column if it's missing:

IF EXISTS (SELECT * FROM INFORMATION_SCHEMA.COLUMNS
           WHERE TABLE_NAME='prefix_topic' AND column_name='topic_last_update')
BEGIN
ALTER TABLE `prefix_topic` ADD `topic_last_update` DATETIME NOT NULL;
UPDATE `prefix_topic` SET `topic_last_update` = `topic_date_add`;
END;

Unfortunately, this code fails due to MySQL's handling of conditional statements involving data manipulation operations.

A Reliable Solution

To reliably check for and create a column in MySQL, try this alternative approach:

SHOW COLUMNS FROM `table` LIKE 'fieldname';

This query retrieves a row only if the specified field name exists in the table. You can then use the results to make decisions in your code.

For example, in PHP:

$result = mysql_query("SHOW COLUMNS FROM `table` LIKE 'fieldname'");
$exists = (mysql_num_rows($result))?TRUE:FALSE;

Conclusion

Checking for and manipulating columns in MySQL requires a different approach than in many other database systems. By utilizing the SHOW COLUMNS query, you can ensure reliable column validation and manipulation in your MySQL applications.

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