Database Query Skill

Building Commands

MySQL

mysql -h "$HOST" -P "$PORT" -u "$USER" --password="$PASS" "$DB" << 'EOSQL'
SQL_QUERY;
EOSQL

Using a heredoc with single-quoted delimiter ('EOSQL') prevents shell expansion inside the SQL. The --password="..." form with double quotes handles special characters (#, !, *, ^) in passwords reliably.

For tabular output add -t. For vertical output add -E. For batch/script output (no borders) omit -t.

PostgreSQL

PGPASSWORD="$PASS" psql -h "$HOST" -p "$PORT" -U "$USER" -d "$DB" -c "SQL_QUERY"

SQL Server

sqlcmd -S "$HOST,$PORT" -U "$USER" -P "$PASS" -d "$DB" -Q "SQL_QUERY"

SQLite

sqlite3 "$DB_PATH" "SQL_QUERY"

Use .headers on and .mode column for readable output:

sqlite3 "$DB_PATH" -header -column "SQL_QUERY"

Safety Rules for Destructive Operations

CRITICAL: Before executing any query that modifies data or schema, you MUST show the full SQL to the user and ask for explicit confirmation using the AskUserQuestion tool. Never run destructive queries silently.

Destructive operations include:

• INSERT, UPDATE, DELETE
• DROP, ALTER, TRUNCATE
• CREATE (tables, indexes, etc.)
• RENAME
• REPLACE
• GRANT, REVOKE
• Any query that is NOT a pure read operation

Read-only operations that can run without confirmation:

• SELECT
• SHOW (tables, databases, columns, indexes, status, etc.)
• DESCRIBE / DESC / EXPLAIN
• USE
• SET (session variables for formatting)

When asking for confirmation, present:

1. The exact SQL that will be executed
2. Which database it targets
3. A brief note on what it will affect (e.g., "This will delete 3 rows from the users table")

If you can, run a SELECT first to show the user what will be affected before asking for confirmation on the destructive query.

Query Formatting Tips

• For large result sets, add LIMIT to avoid overwhelming output
• Use COUNT(*) first when the user asks "how many" questions
• When exploring a database, start with SHOW TABLES or equivalent
• For schema inspection, use DESCRIBE table_name or equivalent
• Quote the password in the CLI command to handle special characters — use double quotes around the password

Password Escaping

Database passwords often contain special shell characters (#, *, !, ^, @, etc.). Use --password="..." with double quotes for MySQL. Pass the SQL via heredoc to avoid shell expansion issues with -e:

mysql -h host -u user --password="pa$$w0rd#!" db << 'EOSQL'
SELECT 1;
EOSQL

Inside double quotes, escape $ as \$, backticks as \`, and " as \". Most other special characters (#, *, !, ^, @) are safe as-is inside double quotes. The single-quoted heredoc delimiter ('EOSQL') prevents any expansion in the SQL body.

Workflow

1. Read .claude/auth/database.json from the project root
2. Determine the database engine from DB_CONNECTION
3. Build the CLI command with proper escaping
4. Classify the query as read-only or destructive
5. If destructive: show the SQL and ask for confirmation before executing
6. Execute and present results clearly
7. If the query fails, read the error, suggest fixes, and retry if appropriate