Command Style (Use PATH)

All examples use the plain command name dbcli (no directory prefix). Ensure dbcli is on PATH instead of hardcoding paths like .\.claude\skills\dbcli\dbcli.exe.

DbCli Compare Skill

Compare results of two SQL queries to verify complete data consistency.

When to Use This Skill

• User wants to compare results of two SQL queries
• User needs to verify query equivalence (e.g., before/after refactoring)
• User asks to validate if two queries produce identical results
• User needs to check if a view matches a complex query
• User wants to verify query optimization didn't change results
• Comparing query results across different time periods or conditions

Comparison Process

The comparison performs five checks:

1. Structure Check - Verify column names, types, and order match
2. Record Count - Compare total number of rows
3. Data Diff (Direction 1) - Find records in query1 not in query2
4. Data Diff (Direction 2) - Find records in query2 not in query1
5. Result Summary - Report complete status

Command Syntax

dbcli compare "QUERY1" "QUERY2" [-c CONNECTION] [-t DBTYPE]

Parameters

• First SQL query (required)
• Second SQL query (required)
• -t, --db-type: Database type (optional, default: "sqlite")
• Environment variables:
  • DBCLI_CONNECTION: Database connection string
  • DBCLI_DBTYPE: Database type (alternative to -t)

Usage Examples

Basic Comparison

# Compare two views
dbcli compare "SELECT * FROM V_ORDERS_NEW" "SELECT * FROM V_ORDERS_OLD"

# Compare table with filtered query
dbcli compare "SELECT * FROM Orders WHERE Status='Active'" "SELECT * FROM Orders_Archive WHERE Status='Active'"

# Compare complex queries
dbcli compare "SELECT CustomerID, SUM(Amount) AS Total FROM Orders GROUP BY CustomerID" "SELECT CustomerID, SUM(Amount) AS Total FROM Orders_V2 GROUP BY CustomerID"

With Connection Options

# SQLite (using environment variables)
export DBCLI_CONNECTION="Data Source=mydb.db"
export DBCLI_DBTYPE="sqlite"
dbcli compare "SELECT * FROM users WHERE active=1" "SELECT * FROM users_v2 WHERE active=1"

# SQL Server
export DBCLI_CONNECTION="Server=localhost;Database=testdb;Trusted_Connection=True"
dbcli -t sqlserver compare "SELECT * FROM Orders" "SELECT * FROM Orders_Backup"

# PostgreSQL
export DBCLI_CONNECTION="Host=localhost;Database=mydb;Username=postgres;Password=pass"
dbcli -t postgresql compare "SELECT * FROM sales WHERE year=2026" "SELECT * FROM sales_archive WHERE year=2026"

Output Format

Successful Match

[1/3] Comparing record counts...
  Query1: 14547 records
  Query2: 14547 records
  ✓ Record counts match (14547 records)

[2/3] Checking differences (query1 - query2)...
  Unique to query1: 0 records

[3/3] Checking differences (query2 - query1)...
  Unique to query2: 0 records

✓ Query results are identical

Data Mismatch

[1/3] Comparing record counts...
  Query1: 1520 records
  Query2: 1518 records
  ✗ Record counts differ

[2/3] Checking differences (query1 - query2)...
  Unique to query1: 5 records

[3/3] Checking differences (query2 - query1)...
  Unique to query2: 3 records

✗ Query results differ (8 total differences)

Exit Codes

• 0 - Query results are completely identical
• 1 - Data or structure mismatch detected

Database Compatibility

MINUS Operator Support

Implementation Note

The dbcli compare command automatically detects the database type and uses the appropriate operator:

• SQLite, PostgreSQL, Microsoft SQL Server: EXCEPT
• DaMeng, Oracle: MINUS

Common Use Cases

Validate Query Refactoring

# Compare original and optimized query
dbcli compare "SELECT * FROM Orders WHERE Status='Active'" "SELECT * FROM Orders WHERE Status IN ('Active')"

Verify View Logic

# Compare view with underlying query
dbcli compare "SELECT * FROM V_SALES_SUMMARY" "SELECT CustomerID, SUM(Amount) AS Total FROM Sales GROUP BY CustomerID"

Check Data Consistency

# Compare data across environments
dbcli compare "SELECT * FROM Users WHERE Active=1" "SELECT * FROM Users_Archive WHERE Active=1"

Troubleshooting

Query Execution Failed

• Verify SQL syntax is correct for the database type
• Check connection string is correct
• Ensure user has SELECT permission on referenced tables
• Test each query individually first: dbcli query "YOUR_SQL"

MINUS Not Supported

• Use EXCEPT for PostgreSQL or SQL Server
• The implementation should handle this automatically based on -t flag

Performance Issues

• For large tables, add WHERE clauses to limit comparison scope
• Use indexed columns in queries for faster comparisons
• Consider comparing aggregated data instead of row-by-row

Related Skills

• dbcli-query - Execute SELECT queries to preview data
• dbcli-tables - List available tables/views
• dbcli-export - Backup data before making changes
• dbcli-view - Manage view definitions