feat: 支持 Option<T> 字段(None↔NULL)、列命名默认原样(Keep)、迁移同名列先删后加,版本 1.1.0

src/migrations/Migrations.cj

@@ -289,6 +289,77 @@ public class DdlFactory {
         }
     }
 
+    /// 解析 AddColumn/AlterColumn 为可执行 SQL 列表（兼容"同名列修改数据结构"场景）：
+    ///   - 库中无同名列 → 单条 ADD COLUMN
+    ///   - 有同名列且类型一致 → AddColumn 幂等跳过（空列表）；AlterColumn 保留原 SQL（处理非空/长度等变化）
+    ///   - 有同名列但类型不同 → 先 DROP COLUMN 再 ADD COLUMN（重建该字段）
+    /// existingType 来自 information_schema.data_type；None 表示列不存在。
+    public func resolveColumnSqls(op: MigrationOperation, dialect: ISqlDialect,
+        existingType: ?String): ArrayList<String> {
+        let result = ArrayList<String>()
+        let col = op.column.getOrThrow()
+        match (existingType) {
+            case None => result.add(toSql(op, dialect))
+            case Some(dbType) =>
+                let target = dialect.columnTypeSql(col.columnType, col.autoIncrement, col.maxLength)
+                if (normalizeTypeName(dbType) == normalizeTypeName(target)) {
+                    // 类型一致：AddColumn 视为幂等跳过；AlterColumn 保留原 SQL
+                    let isAlter = match (op.kind) {
+                        case MigrationOperationKind.AlterColumn => true
+                        case _ => false
+                    }
+                    if (isAlter) {
+                        result.add(toSql(op, dialect))
+                    }
+                } else {
+                    // 类型不同：先删除老字段，再新增新字段
+                    let drop = MigrationOperation(MigrationOperationKind.DropColumn)
+                    drop.tableName = op.tableName
+                    drop.columnName = col.name
+                    result.add(toSql(drop, dialect))
+                    result.add(toSql(op, dialect))
+                }
+        }
+        result
+    }
+
+    /// 类型名归一化：方言 SQL 类型 ↔ information_schema.data_type，统一为小写基础类型（忽略长度/精度括号）。
+    public static func normalizeTypeName(t: String): String {
+        let lower = asciiLower(t)
+        let base = if (let Some(i) <- lower.indexOf("(")) { lower[0..i] } else { lower }
+        match (base) {
+            case "bigserial" | "bigint" | "int8" => "bigint"
+            case "serial" | "integer" | "int" | "int4" => "integer"
+            case "smallint" | "int2" => "smallint"
+            case "varchar" | "character varying" => "varchar"
+            case "character" | "char" | "bpchar" => "char"
+            case "text" => "text"
+            case "boolean" | "bool" => "boolean"
+            case "double precision" | "float8" => "double precision"
+            case "real" | "float4" => "real"
+            case "timestamp" | "timestamp without time zone" | "timestamp with time zone" => "timestamp"
+            case "decimal" | "numeric" => "decimal"
+            case "bytea" => "bytea"
+            case _ => base
+        }
+    }
+
+    /// ASCII 大写转小写（A-Z → a-z，其余字符不变；仅依赖切片与 indexOf，避免 std String 缺失 API）
+    private static func asciiLower(s: String): String {
+        let upper = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
+        let lower = "abcdefghijklmnopqrstuvwxyz"
+        let sb = StringBuilder()
+        for (i in 0..s.size) {
+            let c = s[i..i + 1]
+            if (let Some(idx) <- upper.indexOf(c)) {
+                sb.append(lower[idx..idx + 1])
+            } else {
+                sb.append(c)
+            }
+        }
+        sb.toString()
+    }
+
     private func createTableSql(op: MigrationOperation, dialect: ISqlDialect): String {
         let sb = StringBuilder()
         sb.append("CREATE TABLE IF NOT EXISTS ${dialect.quoteName(op.tableName)} (\n")