fix(mysql): 显式配置的 group_concat_max_len 稳定生效并补充连接表单提示 (#9582)

DBX 连接 MySQL 时会执行 SET SESSION group_concat_max_len = 1048576，
避免 GROUP_CONCAT 结果被静默截断（#2775）。但当用户在 URL 参数里用
Connector/J 语法 sessionVariables=group_concat_max_len=... 显式指定值时，
内置语句与用户语句的执行先后取决于底层驱动，覆盖行为不具备确定性；
连接表单也没有任何提示，导致按服务端配置排查问题时被误导（#9412）。

- 新增显式覆盖检测：解析 sessionVariables 中的赋值目标，命中
  group_concat_max_len（含大小写、@ 前缀、session 限定）时不再下发内置的
  SET SESSION，用户/服务端的值始终生效；@user 变量与 @@global. 赋值不影响
  默认行为。
- 连接表单 URL 参数下方为 MySQL 增加提示，说明可用的覆盖写法
  （sessionVariables=group_concat_max_len=@@global.group_concat_max_len 即
  完全跟随服务端配置），并补齐 10 个语言包文案。

Co-authored-by: zipg <4047349+zipg@users.noreply.github.com>

apps/desktop/src/components/connection/ConnectionDialog.vue

@@ -8200,6 +8200,9 @@ function openExternalUrl(url: string) {
                         <p v-if="showGenericUrlParamsHint" class="text-xs leading-5 text-muted-foreground">
                           {{ t("connection.localInfilePathHint") }}
                         </p>
+                        <p v-if="form.db_type === 'mysql'" class="text-xs leading-5 text-muted-foreground">
+                          {{ t("connection.sessionVariablesHint") }}
+                        </p>
                       </div>
                     </div>
 

apps/desktop/src/i18n/locales/az.ts

@@ -602,6 +602,8 @@ export default withEnglishFallback({
     driverName: "Drayverin adı",
     driverNamePlaceholder: "Təchizatçının və ya mühitin adı",
     urlParams: "URL parametrləri",
+    sessionVariablesHint:
+      "DBX qoşulma zamanı group_concat_max_len sessiya dəyişənini 1048576-ya qaldırır ki, GROUP_CONCAT nəticələri səssizcə kəsilməsin. Server konfiqurasiyasına uyğun olmaq üçün sessionVariables=group_concat_max_len={'@'}{'@'}global.group_concat_max_len yazın (MySQL Connector/J sintaksisi; bir neçə dəyişəni vergüllə ayırın).",
     localInfilePathHint: "LOAD DATA LOCAL INFILE üçün hər faylı localInfilePath=/absolute/path/file.csv ilə ayrıca icazə siyahısına əlavə edin. Əlavə fayllar üçün parametri təkrarlayın.",
     d1AccountId: "Hesabın ID-si",
     d1DatabaseId: "Verilənlər bazasının ID-si",

apps/desktop/src/i18n/locales/en.ts

@@ -745,6 +745,8 @@ export default {
     driverName: "Driver Name",
     driverNamePlaceholder: "Vendor or environment name",
     urlParams: "URL Params",
+    sessionVariablesHint:
+      "DBX raises the session variable group_concat_max_len to 1048576 so GROUP_CONCAT results are not silently truncated. To follow the server configuration instead, use sessionVariables=group_concat_max_len={'@'}{'@'}global.group_concat_max_len (MySQL Connector/J syntax; separate multiple variables with commas).",
     localInfilePathHint: "For LOAD DATA LOCAL INFILE, whitelist each file explicitly with localInfilePath=/absolute/path/file.csv. Repeat the parameter for additional files.",
     d1AccountId: "Account ID",
     d1DatabaseId: "Database ID",

apps/desktop/src/i18n/locales/es.ts

@@ -724,6 +724,8 @@ export default withEnglishFallback({
     driverName: "Nombre del driver",
     driverNamePlaceholder: "Nombre del proveedor o entorno",
     urlParams: "Parámetros de URL",
+    sessionVariablesHint:
+      "DBX eleva la variable de sesión group_concat_max_len a 1048576 para que los resultados de GROUP_CONCAT no se trunquen de forma silenciosa. Para seguir la configuración del servidor, use sessionVariables=group_concat_max_len={'@'}{'@'}global.group_concat_max_len (sintaxis de MySQL Connector/J; separe varias variables con comas).",
     d1AccountId: "ID de cuenta",
     d1DatabaseId: "ID de base de datos",
     d1ApiToken: "Token de API",

apps/desktop/src/i18n/locales/it.ts

@@ -723,6 +723,8 @@ export default withEnglishFallback({
     driverName: "Nome Driver",
     driverNamePlaceholder: "Nome del fornitore o dell'ambiente",
     urlParams: "Parametri URL",
+    sessionVariablesHint:
+      "DBX innalza la variabile di sessione group_concat_max_len a 1048576 per evitare che i risultati di GROUP_CONCAT vengano troncati silenziosamente. Per seguire la configurazione del server, usare sessionVariables=group_concat_max_len={'@'}{'@'}global.group_concat_max_len (sintassi MySQL Connector/J; separare più variabili con virgole).",
     d1AccountId: "ID account",
     d1DatabaseId: "ID database",
     d1ApiToken: "Token API",

apps/desktop/src/i18n/locales/ja.ts

@@ -723,6 +723,8 @@ export default withEnglishFallback({
     driverName: "ドライバー名",
     driverNamePlaceholder: "ベンダー名または環境名",
     urlParams: "URLパラメータ",
+    sessionVariablesHint:
+      "DBX は接続時にセッション変数 group_concat_max_len を 1048576 に引き上げ、GROUP_CONCAT の結果が黙って切り捨てられるのを防ぎます。サーバー設定に合わせる場合は sessionVariables=group_concat_max_len={'@'}{'@'}global.group_concat_max_len を指定してください（MySQL Connector/J と同じ構文、複数の変数はカンマ区切り）。",
     d1AccountId: "アカウントID",
     d1DatabaseId: "データベースID",
     d1ApiToken: "APIトークン",

apps/desktop/src/i18n/locales/ko.ts

@@ -737,6 +737,8 @@ export default withEnglishFallback({
     driverName: "드라이버 이름",
     driverNamePlaceholder: "공급자 또는 환경 이름",
     urlParams: "URL 매개변수",
+    sessionVariablesHint:
+      "DBX는 연결 시 세션 변수 group_concat_max_len을 1048576으로 올려 GROUP_CONCAT 결과가 조용히 잘리는 것을 방지합니다. 서버 설정을 따르려면 sessionVariables=group_concat_max_len={'@'}{'@'}global.group_concat_max_len를 입력하세요(MySQL Connector/J 문법, 여러 변수는 쉼표로 구분).",
     localInfilePathHint: "For LOAD DATA LOCAL INFILE, whitelist each file explicitly with localInfilePath=/absolute/path/file.csv. Repeat the parameter for additional files.",
     d1AccountId: "계정 ID",
     d1DatabaseId: "데이터베이스 ID",

apps/desktop/src/i18n/locales/pt-BR.ts

@@ -724,6 +724,8 @@ export default withEnglishFallback({
     driverName: "Nome do Driver",
     driverNamePlaceholder: "Nome do fornecedor ou ambiente",
     urlParams: "Parâmetros da URL",
+    sessionVariablesHint:
+      "O DBX eleva a variável de sessão group_concat_max_len para 1048576 para que os resultados de GROUP_CONCAT não sejam truncados silenciosamente. Para seguir a configuração do servidor, use sessionVariables=group_concat_max_len={'@'}{'@'}global.group_concat_max_len (sintaxe do MySQL Connector/J; separe várias variáveis com vírgulas).",
     d1AccountId: "ID da conta",
     d1DatabaseId: "ID do banco de dados",
     d1ApiToken: "Token da API",

apps/desktop/src/i18n/locales/tr.ts

@@ -604,6 +604,8 @@ export default withEnglishFallback({
     driverName: "Sürücü Adı",
     driverNamePlaceholder: "Sağlayıcı veya ortam adı",
     urlParams: "URL Parametreleri",
+    sessionVariablesHint:
+      "DBX bağlantı sırasında group_concat_max_len oturum değişkenini 1048576 değerine yükseltir; böylece GROUP_CONCAT sonuçları sessizce kesilmez. Sunucu yapılandırmasını izlemek için sessionVariables=group_concat_max_len={'@'}{'@'}global.group_concat_max_len kullanın (MySQL Connector/J söz dizimi; birden fazla değişkeni virgülle ayırın).",
     localInfilePathHint: "LOAD DATA LOCAL INFILE için her dosyayı localInfilePath=/mutlak/yol/dosya.csv ile açıkça izin listesine ekleyin. Ek dosyalar için parametreyi tekrarlayın.",
     d1AccountId: "Hesap Kimliği",
     d1DatabaseId: "Veritabanı Kimliği",

apps/desktop/src/i18n/locales/zh-CN.ts

@@ -661,6 +661,7 @@ export default withEnglishFallback({
     driverName: "驱动名称",
     driverNamePlaceholder: "厂商或环境名称",
     urlParams: "URL 参数",
+    sessionVariablesHint: "DBX 连接时会把会话变量 group_concat_max_len 提升到 1048576，避免 GROUP_CONCAT 结果被静默截断。如需跟随服务端配置，可填写 sessionVariables=group_concat_max_len={'@'}{'@'}global.group_concat_max_len（语法同 MySQL Connector/J，多个变量用逗号分隔）。",
     localInfilePathHint: "使用 LOAD DATA LOCAL INFILE 时，请通过 localInfilePath=/绝对路径/file.csv 明确授权文件；多个文件需重复填写该参数。",
     d1AccountId: "Account ID",
     d1DatabaseId: "Database ID",

apps/desktop/src/i18n/locales/zh-TW.ts

@@ -727,6 +727,7 @@ export default withEnglishFallback({
     driverName: "驅動程式名稱",
     driverNamePlaceholder: "廠商或環境名稱",
     urlParams: "URL 參數",
+    sessionVariablesHint: "DBX 連線時會把工作階段變數 group_concat_max_len 提升到 1048576，避免 GROUP_CONCAT 結果被靜默截斷。若要跟隨伺服器設定，可填寫 sessionVariables=group_concat_max_len={'@'}{'@'}global.group_concat_max_len（語法同 MySQL Connector/J，多個變數以逗號分隔）。",
     d1AccountId: "帳戶 ID",
     d1DatabaseId: "資料庫 ID",
     d1ApiToken: "API Token",

crates/dbx-drivers/src/db/mysql.rs

@@ -1257,10 +1257,16 @@ impl MySqlTcpKeepaliveMode {
 const MYSQL_GROUP_CONCAT_MAX_LEN: u64 = 1_048_576;
 
 impl MySqlSetupMode {
-    fn group_concat_max_len_query(self) -> Option<String> {
+    fn group_concat_max_len_query(self, url: &str) -> Option<String> {
         match self {
-            Self::Standard => Some(format!("SET SESSION group_concat_max_len = {MYSQL_GROUP_CONCAT_MAX_LEN}")),
-            Self::Compatible => None,
+            // An explicit Connector/J style `sessionVariables=group_concat_max_len=...`
+            // is the user's own choice (for example following the server
+            // configuration with `@@global.group_concat_max_len`), so the built-in
+            // safety default must not overwrite it.
+            Self::Standard if !mysql_session_variables_override_group_concat_max_len(url) => {
+                Some(format!("SET SESSION group_concat_max_len = {MYSQL_GROUP_CONCAT_MAX_LEN}"))
+            }
+            Self::Standard | Self::Compatible => None,
         }
     }
 }
@@ -1532,8 +1538,9 @@ fn mysql_setup_queries_for_database_with_mode(
     queries.push(format!("SET NAMES {charset}"));
     // MySQL defaults group_concat_max_len to 1024, which silently truncates
     // GROUP_CONCAT results. Skip it for MySQL protocol-compatible databases
-    // such as old StarRocks versions that reject unknown MySQL variables.
-    if let Some(query) = setup_mode.group_concat_max_len_query() {
+    // such as old StarRocks versions that reject unknown MySQL variables, and
+    // for connections that configure the variable themselves.
+    if let Some(query) = setup_mode.group_concat_max_len_query(url) {
         queries.push(query);
     }
     queries.extend(extra_setup_queries.iter().cloned());
@@ -1677,15 +1684,49 @@ fn mysql_connection_catalog(url: &str) -> Option<String> {
     })
 }
 
-fn mysql_connection_session_variables(url: &str) -> Option<String> {
-    let (_, query) = url.split_once('?')?;
+/// Parses the Connector/J style `sessionVariables=` URL parameter into raw
+/// `name=value` assignments, keeping user variables (`@name=...`) untrimmed.
+fn mysql_connection_session_variable_assignments(url: &str) -> Vec<String> {
+    let Some((_, query)) = url.split_once('?') else {
+        return Vec::new();
+    };
     let query = query.split('#').next().unwrap_or(query);
-    let value = query.split('&').find_map(|segment| {
+    let Some(value) = query.split('&').find_map(|segment| {
         let (key, value) = segment.split_once('=')?;
         percent_decode_str(key).decode_utf8().ok().filter(|key| key.eq_ignore_ascii_case("sessionVariables"))?;
         percent_decode_str(value).decode_utf8().ok().map(|value| value.into_owned())
-    })?;
-    let assignments = split_mysql_session_variables(&value);
+    }) else {
+        return Vec::new();
+    };
+
+    split_mysql_session_variables(&value)
+}
+
+/// Detects an explicit `group_concat_max_len` assignment in the connection URL.
+/// DBX raises the variable during connection setup, but a value the user (or the
+/// server) asks for must always win, independent of statement execution order.
+fn mysql_session_variables_override_group_concat_max_len(url: &str) -> bool {
+    mysql_connection_session_variable_assignments(url).into_iter().any(|assignment| {
+        let Some((name, _)) = assignment.trim().split_once('=') else {
+            return false;
+        };
+        let name = name.trim();
+        // `@@global.name=...` only changes the global value and `@name=...`
+        // declares a session user variable; neither replaces DBX's session SET.
+        if name.starts_with("@@global.") {
+            return false;
+        }
+        let name = name.strip_prefix("@@").unwrap_or(name);
+        if name.starts_with('@') {
+            return false;
+        }
+        let name = name.strip_prefix("session.").unwrap_or(name);
+        name.trim().eq_ignore_ascii_case("group_concat_max_len")
+    })
+}
+
+fn mysql_connection_session_variables(url: &str) -> Option<String> {
+    let assignments = mysql_connection_session_variable_assignments(url);
     if assignments.is_empty() {
         return None;
     }
@@ -8354,6 +8395,70 @@ mod tests {
         );
     }
 
+    #[test]
+    fn mysql_setup_queries_respect_explicit_group_concat_max_len() {
+        // An explicit value from the connection wins over the safety default.
+        assert_eq!(
+            mysql_setup_queries("mysql://host:3306/db?sessionVariables=group_concat_max_len%3D2048", &[]),
+            vec!["USE `db`", "SET SESSION group_concat_max_len=2048", "SET NAMES utf8mb4"]
+        );
+        assert_eq!(
+            mysql_setup_queries(
+                "mysql://host:3306/db?sessionVariables=query_timeout%3D60%2Cgroup_concat_max_len%3D512",
+                &[]
+            ),
+            vec!["USE `db`", "SET SESSION query_timeout=60,SESSION group_concat_max_len=512", "SET NAMES utf8mb4"]
+        );
+    }
+
+    #[test]
+    fn mysql_setup_queries_follow_server_group_concat_max_len() {
+        // `@@global.group_concat_max_len` keeps DBX aligned with the server value.
+        assert_eq!(
+            mysql_setup_queries(
+                "mysql://host:3306/db?sessionVariables=group_concat_max_len%3D%40%40global.group_concat_max_len",
+                &[],
+            ),
+            vec!["USE `db`", "SET SESSION group_concat_max_len=@@global.group_concat_max_len", "SET NAMES utf8mb4",]
+        );
+    }
+
+    #[test]
+    fn mysql_setup_queries_match_group_concat_max_len_case_insensitively() {
+        assert_eq!(
+            mysql_setup_queries("mysql://host:3306/db?sessionVariables=GROUP_CONCAT_MAX_LEN%3D512", &[]),
+            vec!["USE `db`", "SET SESSION GROUP_CONCAT_MAX_LEN=512", "SET NAMES utf8mb4"]
+        );
+        assert_eq!(
+            mysql_setup_queries("mysql://host:3306/db?sessionVariables=%40%40session.group_concat_max_len%3D512", &[],),
+            vec!["USE `db`", "SET @@session.group_concat_max_len=512", "SET NAMES utf8mb4"]
+        );
+    }
+
+    #[test]
+    fn mysql_setup_queries_keep_group_concat_default_for_other_session_variables() {
+        // A session user variable (or a global-only assignment) must not disable
+        // the built-in safety default.
+        assert_eq!(
+            mysql_setup_queries("mysql://host:3306/db?sessionVariables=%40group_concat_max_len%3D2048", &[]),
+            vec![
+                "USE `db`",
+                "SET @group_concat_max_len=2048",
+                "SET NAMES utf8mb4",
+                "SET SESSION group_concat_max_len = 1048576",
+            ]
+        );
+        assert_eq!(
+            mysql_setup_queries("mysql://host:3306/db?sessionVariables=%40%40global.group_concat_max_len%3D512", &[]),
+            vec![
+                "USE `db`",
+                "SET @@global.group_concat_max_len=512",
+                "SET NAMES utf8mb4",
+                "SET SESSION group_concat_max_len = 1048576",
+            ]
+        );
+    }
+
     #[test]
     fn mysql_setup_queries_apply_explicit_time_zone() {
         assert_eq!(