<p>The warning appears when MySQL cannot apply the MERGE algorithm to a view and falls back to a temporary table approach.</p>
<p>MySQL Error 1354: ER_WARN_VIEW_MERGE means the optimizer cannot merge the view into the query and reverts to a slower temporary table algorithm. Redefine the view with deterministically updatable columns or force the TEMPTABLE algorithm to resolve the warning.</p>
View merge algorithm can't be used here for now (assumed
MySQL issues this warning when a view declared with ALGORITHM=MERGE cannot actually be merged into the outer query during execution. Instead, the server silently switches to the TEMPTABLE algorithm and stores the view result in a temporary table.
The message does not stop query execution, but it signals that the expected performance benefit of MERGE is lost. Addressing the root cause restores efficiency and avoids unnecessary disk usage.
The MERGE algorithm only works when every column in the view maps unambiguously to a single table column and no aggregated or non-deterministic constructs exist. If these rules are broken, MySQL downgrades to TEMPTABLE and emits the warning.
The error also occurs when the view references stored functions that are not deterministic or when the underlying tables use different character sets or collations that block direct merging.
Redesign the view so that each column is updatable and deterministic. Remove GROUP BY, DISTINCT, LIMIT, subqueries, and non-deterministic functions from the view definition where possible.
Alternatively, explicitly set ALGORITHM=TEMPTABLE in the CREATE VIEW statement to silence the warning when merge conditions cannot be met.
Aggregated reporting views often trigger the warning because GROUP BY makes columns non-directly-updatable. Split reporting logic into separate queries or materialized tables.
Views that join tables with different collations can be merged by aligning collations using ALTER TABLE ... CONVERT TO CHARACTER SET ... COLLATE ... before recreating the view.
Always specify the intended algorithm in CREATE VIEW. If MERGE is required, test the view with EXPLAIN to confirm mergeability.
Document view limitations in Galaxy Collections so teammates do not unknowingly add disallowed constructs that break MERGE.
Warnings 1356 (ER_VIEW_CHECK_FAILED) and 1357 (ER_VIEW_SELECT_CLAUSE) also concern view definitions. Handle them similarly by validating column updatability and removing illegal clauses.
Using NOW(), RAND(), or other non-deterministic functions in the select list prevents merging.
GROUP BY, DISTINCT, HAVING, and aggregate functions create derived columns that block direct column mapping.
The presence of LIMIT requires intermediate materialization, so MERGE is disallowed.
Joining tables with different collations forces MySQL to store results in a temporary table.
Occurs when a view references nonexistent fields or tables. Fix by correcting the SELECT clause.
Raised when a view contains illegal clauses such as ORDER BY without LIMIT in subqueries.
Triggers when a view with WITH CHECK OPTION violates its own WHERE condition on insert or update.
No. It is a warning. The query still runs, but performance may degrade.
Run EXPLAIN on a query against the view. A merged view shows the base tables directly instead of a derived table.
If performance is acceptable, you may leave the view as is or declare ALGORITHM=TEMPTABLE to suppress the message.
Galaxy surfaces warnings immediately in the editor and lets you share corrected view definitions through Collections, preventing re-introduction of merge-blocking clauses.
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