<p>MySQL aborts a query when a subquery chain exceeds the allowed nesting depth.</p>
<p>MySQL Error 1473: ER_TOO_HIGH_LEVEL_OF_NESTING_FOR_SELECT appears when a SELECT statement contains more nested subqueries or view layers than the server limit (default 61). Flatten the query, rewrite with joins or temporary tables, or raise the optimizer_switch setting to remove the error.</p>
Too high level of nesting for select
The server raises this error when a SELECT statement, or a view used by the statement, contains subqueries nested deeper than the internal limit (default 61 levels in recent MySQL versions).
MySQL tracks nesting across direct subqueries, derived tables, common table expressions, and cascaded views. When the stack exceeds the threshold, execution stops to protect the optimizer from runaway recursion.
The error shows immediately after the query parser finishes analyzing the statement; no rows are fetched. It affects both interactive sessions and stored program execution.
The same limit applies across MySQL editions, including Aurora MySQL and MariaDB forks that retained the MySQL parser.
Excessive nesting harms performance, confuses maintainers, and may mask logical bugs. Production jobs can fail silently, and ORMs may generate deeply nested SQL that suddenly breaks under heavy refactoring.
Eliminating the error restores query execution and often yields faster plans with lower memory usage.
Deeply chained subqueries created by ORMs or query builders are the most frequent trigger. Each SELECT wrapped inside another counts toward the limit.
Views referencing other views can push the effective depth far beyond what developers see in the final statement.
Recursive common table expressions can also build many layers if not terminated early.
Flatten the query by replacing unnecessary subqueries with joins or derived tables that sit only one level deep.
Materialize complex view hierarchies into temporary tables before running the final SELECT.
As a short term workaround, raise the nesting limit with the optimizer_switch option during the session, but this is not recommended for long term stability.
ORM generated SQL: Inspect the raw query string, add explicit joins, or split large report queries into smaller pieces.
Legacy reporting views: Unwind the view chain and consolidate logic into a single authoritative view endorsed inside Galaxy.
Recursive CTE misuse: Add MAXRECURSION style guards or replace with iterative procedures.
Enforce code reviews that flag more than three nested subqueries.
Use Galaxy collections to store endorsed, flattened versions of common metrics queries so developers do not reinvent deeply nested variants.
Monitor the information_schema.VIEWS definition length; exploding text often hints at excessive nesting.
Error 1116: Too many tables - Happens when join count, not nesting depth, is exceeded. Break the query apart.
Error 1242: Subquery returns more than one row - Limit rows or use aggregation.
Error 1064: Syntax error - Occasionally appears after quick manual rewrites aimed at fixing 1473; always validate syntax.
Each additional SELECT inside parentheses adds one level, quickly breaching the server limit.
Nested views hide complexity; the parser expands them and counts every internal SELECT.
Poor stop conditions can grow recursion levels to hundreds, hitting the same cap.
Object mappers sometimes wrap each filter in separate derived tables.
Triggered when a query joins over the table limit; split joins or use temp tables.
Occurs when a scalar subquery yields multiple results; apply LIMIT 1 or aggregation.
Appears for features unavailable in the current engine, often alongside nesting rewrites.
You cannot; the depth is hard-coded. Only local optimizer switches provide partial relief.
No significant change: MySQL 5.7 and 8.0 both cap at roughly 61 nested SELECT layers.
Galaxy's AI copilot can suggest flattened rewrites and highlight subquery depth during review, but execution stays under your control.
Indirectly. The limit protects memory and stack depth, but the root cause is logical query structure.
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