Error map
Subquery returns more than 1 row Subquery returns more than 1 row (MySQL 1242) / more than one row returned by a subquery used as an expression
SQL · layer 5, Data
Centre: this error. First ring: errors it is linked with (7). Outer ring: what those are linked with. Colours show the layer of a request each error belongs to. Click any dot to re-centre the map on it; hover to follow its connections. The centre dot opens the error page.
Directly related (7)
MySQL ERROR 1062 (23000): Duplicate entry for key
An INSERT/UPDATE would create a duplicate value in a PRIMARY or UNIQUE key.
Column must appear in the GROUP BY clause / isn't in GROUP BY (MySQL 1055 only_full_group_by)
You selected a column that is neither grouped nor aggregated, so the result would be ambiguous.
MySQL ERROR 1093 (HY000): You can't specify target table 'x' for update in FROM clause
An UPDATE/DELETE uses a subquery that reads from the same table, which MySQL doesn’t allow directly.
IncorrectResultSizeDataAccessException: query did not return a unique result: 2
A query expected one row but found several.
MySQL ERROR 1241 (21000): Operand should contain 1 column(s)
A subquery or expression returned several columns where only one is expected.
MySQL ERROR 1248 (42000): Every derived table must have its own alias
A subquery in FROM wasn’t given an alias.
InvalidOperationException: Sequence contains no elements / more than one element
LINQ `First()`, `Single()`, `Last()` or `Max()` ran on an empty sequence (or `Single()` found several items).
Two steps away (20)
MySQL ERROR 1452: Cannot add or update a child row: a foreign key constraint fails
You inserted/updated a row whose foreign key value doesn’t exist in the referenced parent table.
Deadlock found when trying to get lock; try restarting transaction
Two transactions waited on each other’s locks; the database killed one so the other could continue.
HTTP 409 Conflict
The request conflicts with the current state of the resource — e.g. a duplicate or an edit based on an outdated version.
MySQL ERROR 1064 (42000): You have an error in your SQL syntax
MySQL couldn’t parse the query. The text after “near” shows where parsing failed.
Column reference is ambiguous / Column 'id' in field list is ambiguous (MySQL 1052)
A column name exists in more than one joined table, so the database doesn’t know which one you mean.
SQL Error: division by zero / Divide by zero error encountered
An expression divided by a value that was 0 for at least one row.
MySQL ERROR 1175 (HY000): You are using safe update mode and you tried to update a table without a WHERE that uses a KEY column
MySQL Workbench’s safe updates mode blocked an UPDATE/DELETE without a key-based WHERE.
ERROR: there is no unique or exclusion constraint matching the ON CONFLICT specification
INSERT … ON CONFLICT (cols) names columns that don’t have a matching unique index/constraint.
ERROR: bind message supplies 2 parameters, but prepared statement requires 1
The number of query parameters sent doesn’t match the $1, $2 … placeholders in the SQL.
org.hibernate.LazyInitializationException: could not initialize proxy - no Session
A lazy-loaded association was accessed after the Hibernate session/transaction closed.
org.hibernate.TransientObjectException: object references an unsaved transient instance - save the transient instance before flushing
An entity references another entity that hasn’t been saved yet, and no cascade is configured.
org.hibernate.exception.ConstraintViolationException: could not execute statement
The database rejected an insert/update because of a constraint (unique, foreign key, not null).
ERROR: could not determine data type of parameter $1
PostgreSQL can’t infer a parameter’s type from context (e.g. $1 IS NULL or SELECT $1).
ERROR: column "x" is of type integer but expression is of type text — HINT: You will need to rewrite or cast the expression.
An INSERT/UPDATE supplies a value of a different type than the column, and PostgreSQL won’t cast implicitly.
sqlite3.OperationalError: near "x": syntax error
SQLite couldn’t parse the statement; the token after “near” is where it stopped.
SQL Server: Incorrect syntax near 'x'. (Msg 102)
T-SQL couldn’t parse the statement near the shown token.
ORA-00933: SQL command not properly ended
Oracle found extra clauses or syntax it doesn’t support at the end of a statement.
System.NullReferenceException: Object reference not set to an instance of an object
Code dereferenced a variable that is `null` — the .NET equivalent of Java’s NullPointerException.
java.util.NoSuchElementException: No value present
Code asked for an element that doesn’t exist — Optional.get() on empty, iterator.next() past the end, Scanner with no input.
EF Core: The LINQ expression 'x' could not be translated. Either rewrite the query in a form that can be translated, or switch to client evaluation explicitly
The query uses C# code EF Core can’t convert to SQL — custom methods, unsupported string/date functions, or complex projections.
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