feat: abstracción DB multi-engine — CRUD genérico y openers para SQLite, Postgres, ClickHouse, DuckDB

Funciones Go con interfaz unificada para operaciones DB: open, close, create_table, exec, query, insert_row, insert_batch.
Openers específicos por engine. Tipo DBConfig para configuración común.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

functions/infra/db_query.go

@@ -0,0 +1,79 @@
+package infra
+
+import (
+	"database/sql"
+	"fmt"
+	"strconv"
+)
+
+// DBQuery executes a SELECT query and returns the results as a slice of maps.
+// Each map key is the column name; values are converted to native Go types:
+// int64, float64, bool, string, []byte, or nil for NULLs.
+func DBQuery(db *sql.DB, query string, args ...any) ([]map[string]any, error) {
+	rows, err := db.Query(query, args...)
+	if err != nil {
+		return nil, fmt.Errorf("db_query: %w", err)
+	}
+	defer rows.Close()
+
+	cols, err := rows.Columns()
+	if err != nil {
+		return nil, fmt.Errorf("db_query: columns: %w", err)
+	}
+	colTypes, err := rows.ColumnTypes()
+	if err != nil {
+		return nil, fmt.Errorf("db_query: column types: %w", err)
+	}
+
+	var results []map[string]any
+	for rows.Next() {
+		// Use RawBytes so we can inspect the raw value before converting.
+		raw := make([]sql.RawBytes, len(cols))
+		ptrs := make([]any, len(cols))
+		for i := range raw {
+			ptrs[i] = &raw[i]
+		}
+		if err := rows.Scan(ptrs...); err != nil {
+			return nil, fmt.Errorf("db_query: scan: %w", err)
+		}
+
+		row := make(map[string]any, len(cols))
+		for i, col := range cols {
+			if raw[i] == nil {
+				row[col] = nil
+				continue
+			}
+			row[col] = convertRaw(raw[i], colTypes[i].DatabaseTypeName())
+		}
+		results = append(results, row)
+	}
+	if err := rows.Err(); err != nil {
+		return nil, fmt.Errorf("db_query: rows: %w", err)
+	}
+	return results, nil
+}
+
+// convertRaw attempts to convert a raw SQL byte slice into a native Go type
+// based on the database column type name hint.
+func convertRaw(b sql.RawBytes, dbType string) any {
+	s := string(b)
+	switch dbType {
+	case "INTEGER", "INT", "BIGINT", "SMALLINT", "TINYINT", "INT2", "INT4", "INT8":
+		if v, err := strconv.ParseInt(s, 10, 64); err == nil {
+			return v
+		}
+	case "REAL", "FLOAT", "DOUBLE", "NUMERIC", "DECIMAL":
+		if v, err := strconv.ParseFloat(s, 64); err == nil {
+			return v
+		}
+	case "BOOLEAN", "BOOL":
+		if v, err := strconv.ParseBool(s); err == nil {
+			return v
+		}
+	case "BLOB":
+		cp := make([]byte, len(b))
+		copy(cp, b)
+		return cp
+	}
+	return s
+}