sql-error-taxonomy 1.1.2

This project analyses SQL statements and labels possible errors or complications.

SQL Error Taxonomy

This repository provides a SQL error taxonomy aimed at supporting uniform error classification in educational and automated settings.

It is based on the taxonomy proposed by Taipalus et al. [^taipalus_errors2018], with revisions introduced in our work to address ambiguities and limitations encountered when applying the taxonomy in automated SQL error-detection pipelines. The revised taxonomy refines error definitions, clarifies labels, and improves suitability for algorithmic classification.

Definitions are grounded in observable properties of queries, with criteria chosen to remain suitable for automated detection while preserving pedagogical interpretability. No assumptions about student intent are made at this level.

Top-level categories

SQL errors can be organized into four categories:

1. Syntax errors: the query contains invalid SQL syntax and cannot be executed. No result set is produced.

   • Example: SELECT WHERE *;
   • This query is invalid since it's missing which columns to select, the entire FROM clause, and it has an invalid condition in the WHERE clause.

2. Semantic errors: the query produces a result set which is always useless, regardless of the data present in the database, and regardless of its data demand.

   • Example: SELECT * FROM table WHERE 1=0;
   • Regardless of the data demand, this query will always return an empty set, since the condition is always false.

3. Logic errors: the query produces a valid set, but it does not satisfy its data demand.

   • Example: SELECT cID FROM customer WHERE city = 'Turin';
   • Data demand: Select the IDs of customers who live in Genoa
   • This query is valid, but it does not satisfy the data demand, since it lists the IDs of customers who live in Turin, instead of those who live in Genoa.

4. Complications: the query satisfies its data demand, but in an overly complex way.

   • Example: SELECT city FROM store GROUP BY city;
   • Data demand: List all cities in which stores are located, without repetitions.
   • Even though the query returns the correct result, using GROUP BY (instead of SELECT DISTINCT) just to remove duplicate values is both less efficient and harder to read.

Taxonomy

You can use the links in the tables below to see detailed information on each error.

For each query, we will be referencing the following schema, adapted from Miedema et Al. [^miedema_identifying2022]. Underlined attributes collectively form the primary key for each table.

Table name	Attributes
customer	cID, cName, street, city, age
store	sID, sName, street, city
product	pID, pName, suffix
inventory	sID, pID, date, quantity, unit_price

Updates and maintenance

Each error type is assigned a unique identifier which is will never be changed or removed, but new IDs may be added in the future.

Existing taxonomies can be updated by running again the error categorization module on the same set of queries, and reclassifying any errors that have changed category or type.

Syntax errors

Definition A syntax error occurs when a SQL query violates the syntactic or typing rules of the SQL language and cannot be executed by the DBMS.

Key properties

• The DBMS rejects the query at parse time or during static validation.
• No result set is produced.
• The error can be detected without knowledge of the data demand.
• The error is independent of the database instance contents.

Pedagogical interpretation Syntax errors typically reflect difficulties with SQL grammar, clause structure, or expression formation, and often arise in early stages of learning.

Ambiguous database object

ID	Name
1	Ambiguous column
2	Ambiguous function

Undefined database object

ID	Name
3	Undefined column
4	Undefined function
5	Undefined parameter
6	Undefined object
7	Invalid schema name
8	Misspellings
9	Synonyms
10	Omitting quotes around character data

Data type mismatch

ID	Name
11	Failure to specify column name twice
12	IS where not applicable
13	Data type mismatch

Illegal aggregate function placement

ID	Name
14	Using aggregate function outside SELECT or HAVING
15	Aggregate functions cannot be nested

Illegal or insufficient grouping

ID	Name
16	Extraneous or omitted grouping column
17	Strange HAVING: HAVING without GROUP BY

Invalid subqueries

ID	Name
18	Too many columns in subquery
19	Missing quantifier

Common syntax error

ID	Name
20	Confusing function with function parameter
21	Using WHERE twice
22	Omitting the FROM clause
23	Comparison with NULL
24	Omitting the semicolon
25	Date time field overflow
26	Duplicate clause
27	Using an undefined correlation name
28	Confusing table names with column names
29	Confusing the order of keywords (e.g., FROM customer SELECT fee)
30	Confusing the syntax of keywords (e.g., LIKE ('A,' 'B'))
31	Omitting commas
32	Unmatched brackets
33	Curly or square brackets
34	Nonstandard keywords or standard keywords in wrong context
35	Nonstandard operators (e.g., &&, || or ==)
36	Additional semicolon
37	Different tuples in set operation

Semantic errors

Definition A semantic error occurs when a SQL query is syntactically valid and executable, but its evaluation is semantically flawed regardless of the data demand, producing a result that is always meaningless.

Key properties

• The query executes successfully.
• The result set is intrinsically invalid (e.g., always empty or logically inconsistent).
• The error can be detected without reference to the intended task.
• The behavior holds for any possible database instance.

Pedagogical interpretation These errors often signal misconceptions about logical conditions, boolean reasoning, or the meaning of operators in SQL.

Inconsistent expression

ID	Name
38	Implied, tautological or inconsistent expression
39	DISTINCT in SUM or AVG
40	DISTINCT that might remove important duplicates
41	Mixing a >0 with IS NOT NULL or empty string with NULL

Inconsistent join

ID	Name
42	NULL in IN/ANY/ALL subquery
43	Join condition on unmatchable column

Duplicate rows

ID	Name
44	Many duplicates

Redundant column output

ID	Name
45	Constant column output
46	Duplicate column output

Logic errors

Definition A logic error occurs when a SQL query is syntactically and semantically valid, but does not satisfy the given data demand.

Key properties

• The query executes successfully.
• A result set is produced.
• The result does not match the expected outcome defined by the data demand.
• Detection requires comparison with at least one correct reference query or specification.

Pedagogical interpretation Logic errors reflect misunderstandings of the problem requirements, relational reasoning, or the mapping between natural language requests and SQL constructs.

Operator error

ID	Name
47	AND instead of OR
48	OR instead of AND
49	Extraneous NOT operator
50	Missing NOT operator
51	Substituting existence negation with <>
52	Incorrect comparison operator or incorrect value compared

Join error

ID	Name
53	Incorrect table reference
54	Missing table reference
55	Extraneous table reference
56	Join condition on incorrect column
57	Join condition with incorrect comparison operator
58	Omitting a join condition
59	Condition on OUTER JOIN

Nesting error

ID	Name
60	Improper nesting of expressions
61	Improper nesting of subqueries

Expression error

ID	Name
62	Extraneous quotes
63	Missing expression
64	Extraneous expression
65	Expression on incorrect column
66	Expression in incorrect clause
67	Wildcards without LIKE
68	Wrong wildcard
69	Invalid wildcard

Projection error

ID	Name
70	Extraneous column in SELECT
71	Missing column from SELECT
72	Missing DISTINCT from SELECT
73	Missing AS from SELECT
74	Missing column from ORDER BY clause
75	Incorrect column in ORDER BY clause
76	Incorrect ordering of rows

Clause error

ID	Name
77	Missing WHERE clause
78	Missing GROUP BY clause
79	Missing HAVING clause
80	Missing ORDER BY clause
81	Missing LIMIT clause
82	Missing OFFSET clause
83	Extraneous WHERE clause
84	Extraneous GROUP BY clause
85	Extraneous HAVING clause
86	Extraneous ORDER BY clause
87	Extraneous LIMIT clause
88	Extraneous OFFSET clause
89	Incorrect LIMIT
90	Incorrect OFFSET

Function error

ID	Name
91	Incorrect function
92	DISTINCT as function parameter where not applicable
93	Missing DISTINCT from function parameter
94	Incorrect column as function parameter

Complications

Definition A complication occurs when a SQL query satisfies the data demand, but does so in an unnecessarily complex, redundant, or non-idiomatic way.

Key properties

• The query returns a correct result set.
• One or more components are redundant, superfluous, or replaceable by simpler constructs.
• Removing or simplifying these components does not change the result.
• Detection requires knowledge of the data demand.

Pedagogical interpretation Complications often indicate partial understanding or overgeneralization of SQL constructs, and provide opportunities for feedback focused on readability, efficiency, and idiomatic query formulation.

Complication

ID	Name
95	Unnecessary complication
96	Unnecessary DISTINCT in SELECT clause
97	Unnecessary table reference
98	Unused correlation name
99	Tables have the same data
100	Correlation name identical to table name
101	Unnecessarily general comparison operator
102	LIKE without wildcards
103	Unnecessarily complicated SELECT in EXISTS subquery
104	IN/EXISTS can be replaced by comparison
105	Unnecessary aggregate function
106	Unnecessary DISTINCT in aggregate function
107	Unnecessary argument of COUNT
108	Unnecessary GROUP BY in EXISTS subquery
109	GROUP BY with singleton groups
110	GROUP BY with only a single group
111	GROUP BY can be replaced with DISTINCT
112	UNION can be replaced by OR
113	Unnecessary column in ORDER BY clause
114	ORDER BY in subquery
115	Inefficient HAVING
116	Inefficient UNION
117	Condition in the subquery can be moved up
118	OUTER JOIN can be replaced by INNER JOIN
119	Unused CTE

Notes

Classification principles

• The four top-level categories are mutually exclusive as primary labels, although a single query may exhibit multiple issues.
• Classification prioritizes observable query behavior over inferred intent.

Identifier design

• Error identifiers are symbolic rather than numeric to avoid implying a fixed ordering.
• This design choice increases robustness to future revisions, additions, or reclassification, without requiring systematic renumbering.

References

[^taipalus_errors2018]: Toni Taipalus, Mikko Siponen, and Tero Vartiainen. 2018. Errors and Complications in SQL Query Formulation. ACM Trans. Comput. Educ. 18, 3, Article 15 (September 2018), 29 pages. https://doi.org/10.1145/3231712

[^miedema_identifying2022]: Daphne Miedema, Efthimia Aivaloglou, and George Fletcher. Identifying SQL misconceptions of novices: Findings from a think-aloud study. ACM Inroads 13.1 (2022): 52-65. https://dx.doi.org/10.1145/3514214