Fix: 修复 SQL Server 修改默认值时报错 (#2190)

* Fix SQL Server default constraint DDL

* Polish SQL Server default display

---------

Co-authored-by: staff <staff@qimaos-MacBook-Pro.local>

crates/dbx-core/src/table_structure_sql/column_alter.rs

@@ -444,12 +444,13 @@ pub(super) fn build_sqlserver_existing_column_sql(
                 .unwrap_or(false);
 
         if has_old_default {
+            let sql_var = sqlserver_default_constraint_sql_var(table, &current_name);
             statements.push(format!(
-                "DECLARE @sql NVARCHAR(MAX);\
-                 SELECT @sql = 'ALTER TABLE {table} DROP CONSTRAINT [' + name + ']'\
-                 FROM sys.default_constraints\
-                 WHERE parent_object_id = OBJECT_ID('{table}') AND parent_column_id = COLUMNPROPERTY(OBJECT_ID('{table}'), '{col_name}', 'ColumnId');\
-                 EXEC sp_executesql @sql;",
+                "DECLARE {sql_var} NVARCHAR(MAX); \
+                 SELECT TOP (1) {sql_var} = N'ALTER TABLE {table} DROP CONSTRAINT ' + QUOTENAME(dc.name) \
+                 FROM sys.default_constraints AS dc \
+                 WHERE dc.parent_object_id = OBJECT_ID(N'{table}') AND dc.parent_column_id = COLUMNPROPERTY(OBJECT_ID(N'{table}'), N'{col_name}', 'ColumnId'); \
+                 IF {sql_var} IS NOT NULL EXEC sp_executesql {sql_var};",
                 table = table.replace('\'', "''"),
                 col_name = current_name.replace('\'', "''")
             ));
@@ -484,6 +485,15 @@ pub(super) fn build_sqlserver_existing_column_sql(
     statements
 }
 
+fn sqlserver_default_constraint_sql_var(table: &str, column_name: &str) -> String {
+    let mut hash = 0x811c_9dc5u32;
+    for byte in table.bytes().chain([0]).chain(column_name.bytes()) {
+        hash ^= u32::from(byte);
+        hash = hash.wrapping_mul(0x0100_0193);
+    }
+    format!("@dbx_default_sql_{hash:08x}")
+}
+
 fn has_sqlserver_identity_change(column: &EditableStructureColumn) -> bool {
     let Some(original) = &column.original else {
         return false;

crates/dbx-core/src/table_structure_sql/tests.rs

@@ -1021,6 +1021,78 @@ fn builds_sql_server_quoted_column_and_index_statements() {
     );
 }
 
+#[test]
+fn sqlserver_default_changes_drop_old_constraints_with_isolated_batches() {
+    let mut sku = column("sku");
+    sku.data_type = "nvarchar(64)".to_string();
+    sku.default_value = "new sku".to_string();
+    sku.original = Some(ColumnInfo {
+        name: "sku".to_string(),
+        data_type: "nvarchar(64)".to_string(),
+        is_nullable: true,
+        column_default: Some("'old sku'".to_string()),
+        is_primary_key: false,
+        extra: None,
+        comment: None,
+    });
+
+    let mut active = column("active");
+    active.data_type = "bit".to_string();
+    active.is_nullable = false;
+    active.default_value = "1".to_string();
+    active.original = Some(ColumnInfo {
+        name: "active".to_string(),
+        data_type: "bit".to_string(),
+        is_nullable: false,
+        column_default: Some("0".to_string()),
+        is_primary_key: false,
+        extra: None,
+        comment: None,
+    });
+
+    let result = build_table_structure_change_sql(TableStructureSqlOptions {
+        database_type: Some(DatabaseType::SqlServer),
+        schema: Some("core".to_string()),
+        table_name: "products".to_string(),
+        columns: vec![sku, active],
+        indexes: Vec::new(),
+        foreign_keys: Vec::new(),
+        triggers: Vec::new(),
+        table_comment: None,
+        original_table_comment: None,
+    });
+
+    assert_eq!(result.warnings, Vec::<String>::new());
+    assert_eq!(result.statements.len(), 4);
+
+    let sku_drop = &result.statements[0];
+    let active_drop = &result.statements[2];
+    let sku_var = sku_drop.strip_prefix("DECLARE ").unwrap().split_once(" NVARCHAR(MAX);").unwrap().0;
+    let active_var = active_drop.strip_prefix("DECLARE ").unwrap().split_once(" NVARCHAR(MAX);").unwrap().0;
+    assert_ne!(sku_var, "@sql");
+    assert_ne!(active_var, "@sql");
+    assert_ne!(sku_var, active_var);
+
+    for (sql, column_name) in [(sku_drop, "sku"), (active_drop, "active")] {
+        assert!(sql.contains("SELECT TOP (1)"));
+        assert!(sql.contains(" + QUOTENAME(dc.name) FROM sys.default_constraints AS dc WHERE "));
+        assert!(sql.contains("OBJECT_ID(N'[core].[products]')"));
+        assert!(sql.contains(&format!("N'{column_name}', 'ColumnId'")));
+        assert!(sql.contains(" IF "));
+        assert!(!sql.contains("]'FROM"));
+        assert!(!sql.contains("constraintsWHERE"));
+    }
+
+    assert_eq!(
+        result.statements[1],
+        "ALTER TABLE [core].[products] ADD CONSTRAINT [DF_products_sku] DEFAULT 'new sku' FOR [sku];"
+    );
+    assert_eq!(
+        result.statements[3],
+        "ALTER TABLE [core].[products] ADD CONSTRAINT [DF_products_active] DEFAULT 1 FOR [active];"
+    );
+}
+
 #[test]
 fn sqlserver_unchanged_foreign_key_does_not_warn_when_saving_other_changes() {
     let mut email = column("email");