fix: preserve composite indexes in generated SQL

src/types/schema.ts

@@ -19,4 +19,5 @@ export interface Index {
   column_name: string;
   is_unique: boolean;
   is_primary: boolean;
+  seq_in_index?: number;
 }

src/utils/sqlGenerator.ts

@@ -157,20 +157,62 @@ export function generateIndexStatements(
   quote: string
 ): string[] {
   const statements: string[] = [];
+  const groupedIndexes = new Map<string, {
+    name: string;
+    is_unique: boolean;
+    is_primary: boolean;
+    columns: Array<{ name: string; seq_in_index?: number; position: number }>;
+  }>();
+
+  indexes.forEach((idx, position) => {
+    const existing = groupedIndexes.get(idx.name);
+    if (existing) {
+      existing.columns.push({
+        name: idx.column_name,
+        seq_in_index: idx.seq_in_index,
+        position,
+      });
+      return;
+    }
+
+    groupedIndexes.set(idx.name, {
+      name: idx.name,
+      is_unique: idx.is_unique,
+      is_primary: idx.is_primary,
+      columns: [{
+        name: idx.column_name,
+        seq_in_index: idx.seq_in_index,
+        position,
+      }],
+    });
+  });
+
+  const renderColumns = (columns: Array<{ name: string; seq_in_index?: number; position: number }>) =>
+    [...columns]
+      .sort((a, b) => {
+        const aSeq = a.seq_in_index ?? Number.MAX_SAFE_INTEGER;
+        const bSeq = b.seq_in_index ?? Number.MAX_SAFE_INTEGER;
+        if (aSeq !== bSeq) return aSeq - bSeq;
+        return a.position - b.position;
+      })
+      .map(col => `${quote}${col.name}${quote}`)
+      .join(', ');
+
+  const indexGroups = [...groupedIndexes.values()];
 
   // Unique indexes (excluding primary keys)
-  const uniqueIndexes = indexes.filter(idx => idx.is_unique && !idx.is_primary);
+  const uniqueIndexes = indexGroups.filter(idx => idx.is_unique && !idx.is_primary);
   uniqueIndexes.forEach(idx => {
     statements.push(
-      `CREATE UNIQUE INDEX ${quote}${idx.name}${quote} ON ${quote}${tableName}${quote} (${quote}${idx.column_name}${quote});`
+      `CREATE UNIQUE INDEX ${quote}${idx.name}${quote} ON ${quote}${tableName}${quote} (${renderColumns(idx.columns)});`
     );
   });
 
   // Non-unique indexes (excluding primary keys)
-  const nonUniqueIndexes = indexes.filter(idx => !idx.is_unique && !idx.is_primary);
+  const nonUniqueIndexes = indexGroups.filter(idx => !idx.is_unique && !idx.is_primary);
   nonUniqueIndexes.forEach(idx => {
     statements.push(
-      `CREATE INDEX ${quote}${idx.name}${quote} ON ${quote}${tableName}${quote} (${quote}${idx.column_name}${quote});`
+      `CREATE INDEX ${quote}${idx.name}${quote} ON ${quote}${tableName}${quote} (${renderColumns(idx.columns)});`
     );
   });
 

tests/utils/sqlGenerator.test.ts

@@ -255,6 +255,43 @@ describe('sqlGenerator utils', () => {
       expect(result[0]).toBe('CREATE INDEX `idx_name` ON `users` (`name`);');
     });
 
+    it('should generate a single statement for composite indexes', () => {
+      const indexes: Index[] = [
+        { name: 'idx_orders_lookup', column_name: 'customer_id', is_unique: false, is_primary: false, seq_in_index: 1 },
+        { name: 'idx_orders_lookup', column_name: 'status', is_unique: false, is_primary: false, seq_in_index: 2 },
+        { name: 'idx_orders_lookup', column_name: 'created_at', is_unique: false, is_primary: false, seq_in_index: 3 },
+        { name: 'idx_orders_lookup', column_name: 'id', is_unique: false, is_primary: false, seq_in_index: 4 },
+      ];
+      const result = generateIndexStatements(indexes, 'orders', '`');
+      expect(result).toEqual([
+        'CREATE INDEX `idx_orders_lookup` ON `orders` (`customer_id`, `status`, `created_at`, `id`);',
+      ]);
+    });
+
+    it('should order composite index columns by sequence', () => {
+      const indexes: Index[] = [
+        { name: 'idx_orders_lookup', column_name: 'id', is_unique: false, is_primary: false, seq_in_index: 4 },
+        { name: 'idx_orders_lookup', column_name: 'customer_id', is_unique: false, is_primary: false, seq_in_index: 1 },
+        { name: 'idx_orders_lookup', column_name: 'created_at', is_unique: false, is_primary: false, seq_in_index: 3 },
+        { name: 'idx_orders_lookup', column_name: 'status', is_unique: false, is_primary: false, seq_in_index: 2 },
+      ];
+      const result = generateIndexStatements(indexes, 'orders', '`');
+      expect(result[0]).toBe(
+        'CREATE INDEX `idx_orders_lookup` ON `orders` (`customer_id`, `status`, `created_at`, `id`);',
+      );
+    });
+
+    it('should generate a single statement for composite unique indexes', () => {
+      const indexes: Index[] = [
+        { name: 'uk_user_email_scope', column_name: 'email', is_unique: true, is_primary: false, seq_in_index: 1 },
+        { name: 'uk_user_email_scope', column_name: 'account_id', is_unique: true, is_primary: false, seq_in_index: 2 },
+      ];
+      const result = generateIndexStatements(indexes, tableName, '`');
+      expect(result).toEqual([
+        'CREATE UNIQUE INDEX `uk_user_email_scope` ON `users` (`email`, `account_id`);',
+      ]);
+    });
+
     it('should generate multiple index statements', () => {
       const indexes: Index[] = [
         { name: 'uk_email', column_name: 'email', is_unique: true, is_primary: false },
@@ -323,6 +360,20 @@ describe('sqlGenerator utils', () => {
       expect(result).toContain('CREATE INDEX `idx_name` ON `users` (`name`);');
     });
 
+    it('should generate CREATE TABLE with composite indexes', () => {
+      const indexes: Index[] = [
+        { name: 'idx_orders_lookup', column_name: 'customer_id', is_unique: false, is_primary: false, seq_in_index: 1 },
+        { name: 'idx_orders_lookup', column_name: 'status', is_unique: false, is_primary: false, seq_in_index: 2 },
+        { name: 'idx_orders_lookup', column_name: 'created_at', is_unique: false, is_primary: false, seq_in_index: 3 },
+        { name: 'idx_orders_lookup', column_name: 'id', is_unique: false, is_primary: false, seq_in_index: 4 },
+      ];
+      const result = generateCreateTableSQL('orders', columns, [], indexes, 'mysql');
+      expect(result).toContain(
+        'CREATE INDEX `idx_orders_lookup` ON `orders` (`customer_id`, `status`, `created_at`, `id`);',
+      );
+      expect(result).not.toContain('CREATE INDEX `idx_orders_lookup` ON `orders` (`status`);');
+    });
+
     it('should generate complete SQL for PostgreSQL', () => {
       const result = generateCreateTableSQL('users', columns, [], [], 'postgresql');
       expect(result).toContain('CREATE TABLE "users" (');