Error
Error Code:
1390
MySQL Error 1390: Prepared Statement Too Many Placeholders
Description
Error 1390 indicates that a SQL prepared statement you are attempting to execute contains more placeholders (parameters) than MySQL's internal limit allows. This typically occurs when constructing very large or complex queries with an excessive number of dynamic values.
Error Message
Prepared statement contains too many placeholders
Known Causes
3 known causesMySQL Internal Parameter Limit
MySQL enforces an internal limit, commonly 65535, on the maximum number of parameters (placeholders like `?` or `:name`) that a single prepared statement can contain.
Application Query Design
The application code is constructing a SQL query with an exceptionally high number of dynamic parameters, often seen in large batch inserts, updates, or complex `IN` clauses.
ORM Inefficient Query Generation
Object-Relational Mappers (ORMs) or database frameworks might generate verbose SQL with a placeholder for every single value in a large dataset, inadvertently exceeding the parameter limit.
Solutions
3 solutions available1. Reduce the Number of Placeholders in the Query easy
The most direct solution is to simplify the SQL query to use fewer placeholders.
1
Examine your SQL query. Identify if you are using placeholders (e.g., `?` in prepared statements) for values that could be dynamically inserted or are part of a fixed set of options.
2
If possible, refactor the query. Consider if you can use a subquery, a temporary table, or a different approach that requires fewer individual parameters.
Example: Instead of `SELECT * FROM users WHERE id IN (?, ?, ?, ...)` for a large list, consider creating a temporary table, inserting the IDs into it, and then joining with the `users` table.3
Alternatively, if the list of values is relatively static or can be grouped, consider breaking the query into multiple smaller prepared statements or a single query with a less dynamic structure.
2. Re-evaluate the Need for a Prepared Statement medium
For queries with a very large, dynamic number of parameters, a prepared statement might not be the most efficient or even feasible approach. Consider alternatives.
1
Assess if the complexity of your query truly warrants a prepared statement. If the number of placeholders is consistently very high and difficult to manage, consider if there's a simpler, non-prepared statement alternative.
2
If you're dealing with a large set of values for an `IN` clause, consider building the SQL string directly (with proper sanitization to prevent SQL injection) if the number of values is within a reasonable limit for direct string construction, or use a temporary table as mentioned in the previous solution.
Example (use with caution and proper sanitization):
sql
SET @ids = '1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20'; -- Example list
SET @query = CONCAT('SELECT * FROM users WHERE id IN (', @ids, ')');
PREPARE stmt FROM @query;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
3
For bulk operations (like inserts), consider using `LOAD DATA INFILE` or multi-row `INSERT` statements, which are generally more efficient and don't rely on prepared statements with a vast number of placeholders.
3. Increase the `max_prepared_stmt_count` Limit (Temporary or Last Resort) advanced
This is a server-side configuration change that increases the maximum number of prepared statements the server can handle, but it's generally not the primary solution and can impact server resources.
1
Understand that this is a workaround and not a fundamental fix for an overly complex query. It can mask underlying architectural issues.
2
Locate your MySQL configuration file (e.g., `my.cnf` or `my.ini`).
3
Add or modify the `max_prepared_stmt_count` parameter in the `[mysqld]` section of your configuration file. Increase the value. The default is often 16382. You might need to experiment to find a suitable value, but be mindful of memory usage.
[mysqld]
max_prepared_stmt_count = 327684
Save the configuration file and restart the MySQL server for the changes to take effect.
Example using systemd (Linux):
systemctl restart mysqld5
Monitor server performance and memory usage after making this change.