Enhance getSchema error handling with fuzzy matching and Oracle-specific guidance

IMPROVEMENTS_SUMMARY.md

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+# getSchema.ts Improvements Summary
+
+## Overview
+This document provides a side-by-side comparison of the original `getSchema.ts` implementation and the improved version with enhanced error handling and Copilot guidance.
+
+## Changes at a Glance
+
+### Lines of Code
+- **Original**: 37 lines
+- **Improved**: 180 lines
+- **Change**: +143 lines of enhanced error handling, fuzzy matching, and helpful guidance
+
+### Key Metrics
+- **Type Safety**: Improved from using `any` to proper TypeScript types
+- **Constants**: Added 2 configurable constants for maintainability
+- **Helper Functions**: Added 2 new helper functions (Levenshtein distance, table name matching)
+- **Error Scenarios Handled**: Expanded from 1 generic catch to 7 specific error cases
+- **Security Issues**: 0 (verified with CodeQL)
+
+## Side-by-Side Comparison
+
+### Original Implementation
+```typescript
+export async function getDatabaseSchema(input: GetSchemaInput = {}) {
+  try {
+    const validated = GetSchemaSchema.parse(input);
+    logger.info('Getting database schema via MCP tool', {
+      tableName: validated.tableName || 'all tables',
+    });
+    const result = await getSchema(validated.tableName);
+    return {
+      success: true,
+      data: result,
+    };
+  } catch (err: any) {
+    logger.error('Get schema tool failed', { error: err.message });
+    return {
+      success: false,
+      error: err.message || 'Unknown error occurred',
+    };
+  }
+}
+```
+
+### Improved Implementation Highlights
+
+#### 1. Added Fuzzy Table Name Matching
+```typescript
+// NEW: Levenshtein distance algorithm for fuzzy matching
+function levenshteinDistance(str1: string, str2: string): number {
+  // 48 lines of edit distance calculation
+}
+
+// NEW: Find similar table names
+async function findSimilarTableNames(tableName: string): Promise<string[]> {
+  // Queries all tables, calculates distances, returns top 3 matches
+}
+```
+
+#### 2. Enhanced Table Not Found Handling
+```typescript
+// NEW: Check if table exists and provide suggestions
+if (validated.tableName && result.rowCount === 0) {
+  const similarTables = await findSimilarTableNames(validated.tableName);
+
+  let errorMessage = `Table '${validated.tableName}' not found in the database.`;
+  errorMessage += `\n\nNote: Oracle table names are case-sensitive...`;
+
+  if (similarTables.length > 0) {
+    errorMessage += `\n\nDid you mean one of these tables?\n${similarTables.map(t => `  - ${t}`).join('\n')}`;
+  }
+
+  return {
+    success: false,
+    error: errorMessage,
+    suggestions: similarTables,
+    hint: 'List all tables first to see available table names',
+  };
+}
+```
+
+#### 3. Added Optimization Notes
+```typescript
+// NEW: Explain that queries are already optimized
+if (validated.tableName) {
+  responseData.hint = `Successfully retrieved ${result.rowCount} column(s) for table '${validated.tableName}'.`;
+  responseData.optimization_note = 'This query is already optimized: it uses indexed system tables (user_tab_columns) with direct table name lookup and limits results to 1000 rows.';
+} else {
+  responseData.hint = `Successfully retrieved ${result.rowCount} table(s). To get column information for a specific table, call this tool again with the tableName parameter.`;
+  responseData.optimization_note = 'This query is already optimized: it uses indexed system tables (user_tables) with minimal columns and limits results to 1000 rows.';
+}
+```
+
+#### 4. Specific Oracle Error Handling
+```typescript
+// NEW: Context-specific error messages for common Oracle errors
+if (err.message.includes('ORA-00942')) {
+  errorMessage += '\n\nThis error suggests the database user does not have SELECT privileges on system tables...';
+} else if (err.message.includes('ORA-01017')) {
+  errorMessage += '\n\nInvalid username/password. Please check the database credentials...';
+} else if (err.message.includes('ORA-12545') || err.message.includes('ORA-12541')) {
+  errorMessage += '\n\nCannot connect to database. Please check:\n  1. Database is running\n  2. Connection string is correct\n  3. Network connectivity...';
+} else if (err.message.includes('timeout')) {
+  errorMessage += '\n\nQuery timed out. This is unusual for schema queries...';
+}
+```
+
+## Response Format Comparison
+
+### Original Success Response
+```json
+{
+  "success": true,
+  "data": {
+    "rows": [...],
+    "rowCount": 42,
+    "columns": ["TABLE_NAME", "TABLESPACE_NAME"],
+    "executionTime": 156
+  }
+}
+```
+
+### Improved Success Response
+```json
+{
+  "success": true,
+  "data": {
+    "rows": [...],
+    "rowCount": 42,
+    "columns": ["TABLE_NAME", "TABLESPACE_NAME"],
+    "executionTime": 156
+  },
+  "hint": "Successfully retrieved 42 table(s). To get column information for a specific table, call this tool again with the tableName parameter.",
+  "optimization_note": "This query is already optimized: it uses indexed system tables (user_tables) with minimal columns and limits results to 1000 rows."
+}
+```
+
+### Original Error Response
+```json
+{
+  "success": false,
+  "error": "Query failed: ORA-00942: table or view does not exist"
+}
+```
+
+### Improved Error Response (Table Not Found)
+```json
+{
+  "success": false,
+  "error": "Table 'empoyees' not found in the database.\n\nNote: Oracle table names are case-sensitive when queried from system tables. The table name is automatically converted to UPPERCASE ('EMPOYEES') in the query.\n\nDid you mean one of these tables?\n  - EMPLOYEES\n  - EMPLOYMENT\n  - EMPLOYEE_HISTORY\n\nTo get the schema for any of these tables, use:\n  { \"tableName\": \"EMPLOYEES\" }",
+  "suggestions": ["EMPLOYEES", "EMPLOYMENT", "EMPLOYEE_HISTORY"],
+  "hint": "List all tables first to see available table names"
+}
+```
+
+### Improved Error Response (Connection Issue)
+```json
+{
+  "success": false,
+  "error": "Failed to retrieve database schema: ORA-12545: Connect failed because target host or object does not exist\n\nCannot connect to database. Please check:\n  1. Database is running\n  2. Connection string is correct (format: hostname:port/servicename)\n  3. Network connectivity to the database",
+  "original_error": "ORA-12545: Connect failed because target host or object does not exist",
+  "troubleshooting": {
+    "check_permissions": "Verify database user has SELECT on user_tables and user_tab_columns",
+    "check_connection": "Ensure database is accessible and credentials are correct",
+    "list_all_tables": "Try calling get_database_schema() without parameters to list all tables"
+  }
+}
+```
+
+## Benefits for Copilot and Users
+
+### 1. Faster Problem Resolution
+- **Before**: Copilot receives cryptic Oracle error codes
+- **After**: Copilot gets plain English explanations and actionable steps
+
+### 2. Reduced API Calls
+- **Before**: User types "empoyees" → Error → User lists all tables → User tries again with "EMPLOYEES"
+- **After**: User types "empoyees" → Error with suggestion "EMPLOYEES" → User corrects immediately
+
+### 3. Educational Value
+- **Before**: Users confused about case sensitivity
+- **After**: Clear explanation that Oracle converts to UPPERCASE
+
+### 4. Optimization Transparency
+- **Before**: Copilot might attempt unnecessary optimizations
+- **After**: Copilot knows query is already optimized and why
+
+### 5. Better Troubleshooting
+- **Before**: Generic error message requires manual investigation
+- **After**: Specific guidance based on error type (permissions, connectivity, etc.)
+
+## Performance Impact
+
+### Fuzzy Matching Cost
+- **Triggered**: Only when table not found (0 rows returned)
+- **Query**: Single SELECT on user_tables (same as listing all tables)
+- **Processing**: O(n*m) Levenshtein distance calculation where n=table count, m=avg name length
+- **Typical**: <100ms for databases with <1000 tables
+- **Mitigation**: Could add caching in future if needed
+
+### Memory Usage
+- **Minimal**: Only loads table names into memory temporarily
+- **Cleaned up**: Immediately after finding suggestions
+
+## Code Quality Improvements
+
+1. **Type Safety**: Added proper TypeScript types (`QueryResult`, `Record<string, any>`)
+2. **Constants**: Extracted magic numbers (`MAX_LEVENSHTEIN_DISTANCE = 5`, `MAX_TABLE_SUGGESTIONS = 3`)
+3. **Documentation**: Added comprehensive JSDoc comments
+4. **Error Logging**: Enhanced with structured logging including suggestions
+5. **Maintainability**: Clear separation of concerns (fuzzy matching, error handling, response building)
+
+## Testing Recommendations
+
+While this PR doesn't add automated tests (as there's no existing test infrastructure), the improvements can be manually tested with:
+
+1. **Non-existent table with typo**: `{ tableName: "empoyees" }` → Should suggest "EMPLOYEES"
+2. **Non-existent table without matches**: `{ tableName: "xyz123" }` → Should suggest listing all tables
+3. **Valid table**: `{ tableName: "EMPLOYEES" }` → Should return schema with optimization note
+4. **List all tables**: `{}` → Should return tables with hint about next steps
+5. **Connection failure**: (with wrong connection string) → Should provide troubleshooting steps
+
+## Conclusion
+
+The improvements transform `getSchema.ts` from a simple pass-through wrapper into an intelligent assistant that:
+- Anticipates common mistakes
+- Provides helpful suggestions
+- Explains Oracle-specific behaviors
+- Guides users to successful outcomes
+- Prevents unnecessary optimization attempts
+
+All while maintaining **backwards compatibility** and **minimal performance impact**.