Compiler and SQL error triage: names, constraints and syntax — DedSec Project

cannot find symbol

Language / environment: Java

Meaning

A name, type or method cannot be resolved at compile time.

Repair

Check imports, package declaration, spelling and method signature.

UNIQUE constraint failed

Exact diagnosis

A UNIQUE index protects business identities or other unique combinations. Duplicate writes can mean repeated requests, bad source data or a race between checking and inserting. A SELECT-before-INSERT check is not atomic; the constraint remains the authority. Treat conflict policies explicitly rather than deleting conflicting rows.

Disposable reproduction or inspection

Run only on an isolated local database or an authorized nonproduction environment.

import sqlite3
db = sqlite3.connect(":memory:")
db.execute("CREATE TABLE jobs(key TEXT PRIMARY KEY, attempts INTEGER NOT NULL)")
sql = """INSERT INTO jobs(key, attempts) VALUES (?, 1)
ON CONFLICT(key) DO UPDATE SET attempts = attempts + 1"""
db.execute(sql, ("job-1",))
db.execute(sql, ("job-1",))
assert db.execute("SELECT attempts FROM jobs WHERE key='job-1'").fetchone()[0] == 2
assert db.execute("SELECT COUNT(*) FROM jobs").fetchone()[0] == 1

Resolution procedure

Define whether the operation is create-only, a true update or a retry of the same event. ON CONFLICT targets a specific uniqueness rule; use it intentionally. INSERT OR REPLACE can delete and reinsert, affecting row IDs, triggers and foreign keys. Store idempotency keys when retries must not increase counts or charges.

Lab and boundary conditions

Change the example so repeating job-1 does not increment attempts. Add a second unique field and test which conflict target is triggered. Verify that unrelated integrity violations still raise instead of being swallowed.

syntax error near

Exact diagnosis

A SQL parser error occurs before a statement can execute. The named token is where the parser became unable to continue, not necessarily where the incorrect delimiter began. Syntax depends on the engine and version: a MySQL clause may not be valid in SQLite or PostgreSQL. Treat values and SQL identifiers differently when constructing statements.

Disposable reproduction or inspection

Run only on an isolated local database or an authorized nonproduction environment.

import sqlite3
db = sqlite3.connect(":memory:")
db.execute("CREATE TABLE measures(value INTEGER)")
bad = "INSERT INTO measures(value,) VALUES (3)"
try:
    db.execute(bad)
except sqlite3.OperationalError as exc:
    assert "syntax" in str(exc).lower()
else:
    raise AssertionError("bad SQL parsed")
db.execute("INSERT INTO measures(value) VALUES (?)", (3,))
assert db.execute("SELECT value FROM measures").fetchone() == (3,)

Resolution procedure

Capture the exact SQL statement with sensitive parameter values redacted. Minimize to the first failing clause while preserving engine/version context. Look for trailing commas, unmatched quotes and reserved identifiers. Parameter placeholders bind values only: choose identifiers from a validated allowlist rather than inserting untrusted column names.

Lab and boundary conditions

Try a table name that is a reserved keyword, repair it with the quoting rules for your chosen SQL engine, and test a parameter containing an apostrophe without manual escaping. Distinguish parser errors from no-such-column errors.