SQL error messages explained
Paste the error your database gave you, or scan the list below. Each page shows the failing query, runs it in your browser, and explains what the database is telling you.
- Fix “Column Must Appear in the GROUP BY Clause” in SQL
A selected column is neither grouped nor aggregated, so this engine cannot derive one value for the group.
must appear in the GROUP BY clause - Fix “Column Not Found” When Filtering on a SQL Alias
In logical order, WHERE comes before SELECT assigns aliases, so many engines reject the alias there.
does not exist - Fix “Ambiguous Column Reference” in a SQL JOIN
Both joined tables have that column name, so the database refuses to guess.
ambiguous - Fix “Aggregate Functions Are Not Allowed in WHERE” in SQL
WHERE filters rows before grouping, so aggregates do not exist yet. Use HAVING.
aggregates - Fix “Window Functions Are Not Allowed in WHERE” in SQL
Window functions are evaluated after WHERE, so you cannot filter on one directly.
window function - Fix “Failing Row Contains” Constraint Errors in SQL
An INSERT or UPDATE broke a NOT NULL or CHECK rule on the table. The detail line shows the row.
Failing row contains - Fix “NOT NULL Constraint Failed” in SQL
A required column got no value. Supply one, give the column a default, or let it be null.
NOT NULL constraint failed - Fix “Duplicate Key Violates Primary Key Constraint” in SQL
The key you are inserting already exists. Find the existing row before you write.
violates primary key constraint - Fix “Violates Foreign Key Constraint” in SQL
A child row points at a parent that is not there, or a parent still has children.
foreign key constraint - Fix “CHECK Constraint Failed” in SQL
A value is storable but breaks a business rule the table enforces. Read the expression.
CHECK constraint failed - Fix “Cannot Insert Into a Generated Column” in SQL
A generated column computes itself. Leave it out of the column list entirely.
Cannot insert into a generated column - Fix “Is of Type View, Trying to Drop Type Table” in SQL
DROP TABLE will not remove a view, and IF EXISTS does not rescue it. Drop the type you made.
trying to drop type Table - Fix “Syntax Error at or Near” in SQL
The parser stopped at the first word it could not use. The quoted token is where it gave up, not always where the mistake is.
syntax error at or near - Fix “Referenced Column Not Found” in SQL
No table in the FROM clause has a column by that name. Usually a typo or a table you did not join.
not found in FROM clause - Fix “Different Number of Columns” in a SQL UNION
Each SELECT in a UNION has to return the same number of columns, in the same order.
different number of columns - Fix “Conversion Error: Could Not Convert String” in SQL
A text value won't cast to the type you asked for. The message names the value, the type, and the column.
Could not convert string - Fix “Catalog Error: Table Does Not Exist” in SQL
No table by that name is visible to the query. A typo, a missing schema, or a table that's already gone.
Table with name - Fix “More Than One Row Returned by a Subquery” in SQL
A subquery used as a single value found several. Use IN, or decide which one row you want.
More than one row returned by a subquery - Fix “Missing FROM-Clause Entry for Table” in SQL
A column is prefixed with a table name or alias the FROM clause doesn't define. Use the alias you gave, or join the table.
missing FROM-clause entry for table - Fix “Operand Should Contain 1 Column(s)” in SQL
A subquery that should return one column returns two. Select only the column you compare, or compare a row of values.
Operand should contain 1 column(s) - Fix “Column Count Doesn't Match Value Count” in SQL
An INSERT supplies a different number of values than the columns it fills. Name the columns, then give one value for each.
Column count doesn't match value count - Fix “No Unique Constraint Matching Given Keys” in SQL
A foreign key points at a column that isn't a primary key or UNIQUE. Give the parent table a key on that column first.
no unique constraint matching given keys
Other errors you will meet
Two more that come up often enough to cover here, though they have no page of their own yet.
No function matches the given name and argument types
A type mismatch, often from comparing text to a number or passing a
string where a date is expected. Cast explicitly with
CAST(x AS INTEGER)
or fix the literal's quotes.
Conversion error / could not convert
A value could not be coerced to the needed type, for example the
text
'N/A'
in a numeric column. Filter or clean the bad values first, or guard
with
TRY_CAST
(DuckDB), which returns
NULL
instead of failing.
If the query runs without complaint and comes back empty, there is nothing here to decode: it succeeded. Read why a query runs but returns no rows instead.
When you get stuck on any of these, rebuild the query in small steps.
Start with
SELECT * FROM table, add one join, then one filter, checking the result after each change.