feat(func/greatest-least): new config param ignore null for func greatest/least

docs/en/14-reference/01-components/01-taosd.md

@@ -491,6 +491,7 @@ The effective value of charset is UTF-8.
 | curRange       |                   | Supported, effective after restart | Internal parameter, used for setting lossy compression       |
 | compressor     |                   | Supported, effective after restart | Internal parameter, used for setting lossy compression       |
 | compareAsStrInGreatest | After 3.4.0.0  | Supported, effective immediately   | Whether to compare values as strings in GREATEST function; default value true |
+| ignoreNullInGreatest   | After 3.4.2.0  | Supported, effective immediately   | Whether GREATEST and LEAST skip NULL arguments; 0 (default): MySQL-compatible, any NULL makes the result NULL; 1: skip NULL arguments and compare only non-NULL values |
 | showFullCreateTableColumn |  After 3.4.0.0 | Supported, effective immediately   | Whether SHOW CREATE TABLE displays full column information; 0: only table name and database name, 1: full create statement; default value 0 |
 | multiResultFunctionStarReturnTags | After 3.4.0.0 | Supported, effective immediately   | Whether multi-result functions return tag columns when using *; default value false |
 

docs/en/14-reference/01-components/02-taosc.md

@@ -47,6 +47,7 @@ The following configuration parameters only take effect for Native connections.
 |minSlidingTime                   |         |Supported, effective immediately  |Internal parameter, minimum allowable value for sliding|
 |minIntervalTime                  |         |Supported, effective immediately  |Internal parameter, minimum allowable value for interval|
 |compareAsStrInGreatest           | v3.3.6.0 |Supported, effective immediately  |When the greatest and least functions have both numeric and string types as parameters, the comparison type conversion rules are as follows: Integer; 1: uniformly converted to string comparison, 0: uniformly converted to numeric type comparison.|
+|ignoreNullInGreatest             | v3.4.2.0 |Supported, effective immediately  |Whether the GREATEST and LEAST functions skip NULL arguments. Integer; 0 (default): MySQL-compatible — any NULL argument makes the result NULL; 1: skip NULL arguments and compare only non-NULL values, returning NULL only when every argument is NULL. Orthogonal to compareAsStrInGreatest.|
 |showFullCreateTableColumn        | Added in 3.3.7.1 | Supported                          | Whether show column compress info while execute `show create table tablname`, range 0/1, default: 0.|
 
 ### Writing Related

docs/en/14-reference/01-components/08-config-scope.md

@@ -74,6 +74,7 @@ This document compares the configuration parameters of taosd (server-side) and t
 | minSlidingTime | taosc | Minimum allowable value for sliding |
 | minIntervalTime | taosc | Minimum allowable value for interval |
 | compareAsStrInGreatest | taosc | Comparison type conversion rules for greatest and least functions |
+| ignoreNullInGreatest | taosc | Whether greatest and least functions skip NULL arguments |
 | showFullCreateTableColumn | taosc | Whether show create table returns column compression information |
 | rpcRecvLogThreshold| taosd| The threshold for warning logs in the RPC module |
 | **Region Related** | | |

docs/en/14-reference/03-taos-sql/22-function.md

@@ -144,13 +144,16 @@ GREATEST(expr1, expr2[, expr]...)
 
 **Comparison rules**: The following rules describe the conversion method of the comparison operation:
 
-- If any parameter is NULL, the comparison result is NULL.
+- If any parameter is NULL, the comparison result is NULL. (See `ignoreNullInGreatest` below to skip NULL arguments instead.)
 - If all parameters in the comparison operation are string types, compare them as string types
 - If all parameters are numeric types, compare them as numeric types.
 - If there are both string types and numeric types in the parameters, according to the `compareAsStrInGreatest` configuration item, they are uniformly compared as strings or numeric values. By default, they are compared as strings.
 - In all cases, when different types are compared, the comparison type will choose the type with a larger range for comparison. For example, when comparing integer types, if there is a BIGINT type, BIGINT will definitely be selected as the comparison type.
 
-**Related configuration items**: Client configuration, compareAsStrInGreatest is 1, which means that both string types and numeric types are converted to string comparisons, and 0 means that they are converted to numeric types. The default is 1.
+**Related configuration items**:
+
+- `compareAsStrInGreatest` (client configuration): `1` means that when both string types and numeric types are present they are uniformly compared as strings; `0` means they are uniformly compared as numeric values. The default is `1`.
+- `ignoreNullInGreatest` (client configuration, available since ver-3.4.2.0): `0` (default) keeps the MySQL-compatible behavior — any NULL argument makes the result NULL. `1` skips NULL arguments and compares only the non-NULL values; if every argument is NULL, the result is still NULL. This option is orthogonal to `compareAsStrInGreatest`: it only controls NULL handling, the comparison rules above for non-NULL values are unchanged.
 
 #### LEAST
 

docs/zh/14-reference/01-components/01-taosd.md

@@ -2630,6 +2630,17 @@ charset 的有效值是 UTF-8。
 - 动态修改：支持通过 SQL 修改，立即生效。
 - 支持版本：从 v3.4.0.0 版本开始引入
 
+#### ignoreNullInGreatest
+
+- 说明：GREATEST、LEAST 函数是否跳过 NULL 参数
+- 类型：整数；0：与 MySQL 一致，任一参数为 NULL 则返回 NULL；1：跳过 NULL 参数，仅在非 NULL 值之间比较，所有参数均为 NULL 时仍返回 NULL。与 compareAsStrInGreatest 正交。
+- 默认值：0
+- 最小值：0
+- 最大值：1
+- 参数类型：局部配置参数
+- 动态修改：支持通过 SQL 修改，立即生效。
+- 支持版本：从 v3.4.2.0 版本开始引入
+
 #### showFullCreateTableColumn
 
 - 说明：SHOW CREATE TABLE 是否显示完整的列信息

docs/zh/14-reference/01-components/02-taosc.md

@@ -277,6 +277,13 @@ taosc 和 taosd 存在许多同名参数，虽然名称相同但作用范围可
 - 动态修改：支持通过 SQL 修改，立即生效
 - 支持版本：从 v3.3.6.0 版本开始引入
 
+#### ignoreNullInGreatest
+
+- 说明：用于决定 greatest、least 函数是否跳过 NULL 参数。
+- 类型：整数；0（默认）：与 MySQL 一致，任一参数为 NULL 则返回 NULL；1：跳过 NULL 参数，仅在非 NULL 值之间比较，所有参数均为 NULL 时仍返回 NULL。与 compareAsStrInGreatest 正交。
+- 动态修改：支持通过 SQL 修改，立即生效
+- 支持版本：从 v3.4.2.0 版本开始引入
+
 #### showFullCreateTableColumn  
 
 - 说明：`show create table` 的返回值是否带 `column` 的压缩信息

docs/zh/14-reference/01-components/08-config-scope.md

@@ -75,6 +75,7 @@ toc_max_heading_level: 4
 | minSlidingTime | taosc | sliding 的最小允许值 |
 | minIntervalTime | taosc | interval 的最小允许值 |
 | compareAsStrInGreatest | taosc | 用于决定 greatest、least 函数的参数既有数值类型又有字符串类型时，比较类型的转换规则 |
+| ignoreNullInGreatest | taosc | 用于决定 greatest、least 函数是否跳过 NULL 参数 |
 | showFullCreateTableColumn | taosc | show create table 的返回值是否带 column 的压缩信息 |
 | **区域相关** | | |
 | timezone | both | 时区 |

docs/zh/14-reference/03-taos-sql/22-function.md

@@ -211,13 +211,16 @@ GREATEST(expr1, expr2[, expr]...)
 
 **比较规则**：以下规则描述了比较操作的转换方式：
 
-- 如果有任何一个参数为 NULL，则比较结果为 NULL。
+- 如果有任何一个参数为 NULL，则比较结果为 NULL。（如需跳过 NULL 参数，参见下方 `ignoreNullInGreatest` 配置项。）
 - 如果比较操作中的所有参数都是字符串类型，按照字符串类型比较
 - 如果所有参数都是数值类型，则将它们作为数值类型进行比较。
 - 如果参数中既有字符串类型，也有数值类型，根据 compareAsStrInGreatest 配置项，统一作为字符串或者数值进行比较。默认按照字符串比较。
 - 在所有情况下，不同类型比较，比较类型会选择范围更大的类型进行比较，例如作为整数类型比较时，如果存在 BIGINT 类型，必定会选择 BIGINT 作为比较类型。
 
-**相关配置项**：客户端配置，compareAsStrInGreatest 为 1 表示同时存在字符串类型和数值类型统一转为字符串比较，为 0 表示统一转为数值类型比较。默认为 1。
+**相关配置项**：
+
+- `compareAsStrInGreatest`（客户端配置）：为 `1` 表示同时存在字符串类型和数值类型时统一转为字符串比较，为 `0` 表示统一转为数值类型比较。默认为 `1`。
+- `ignoreNullInGreatest`（客户端配置，自 ver-3.4.2.0 起支持）：为 `0`（默认）时保持与 MySQL 一致的行为，任一参数为 NULL 则结果为 NULL；为 `1` 时跳过 NULL 参数，仅在非 NULL 值之间进行比较，若所有参数均为 NULL 仍返回 NULL。该项与 `compareAsStrInGreatest` 正交，仅影响 NULL 参数的处理，非 NULL 值之间的比较规则不变。
 
 #### LEAST
 

include/common/tglobal.h

@@ -387,6 +387,7 @@ extern int32_t tsStreamNotifyMessageSize;
 extern int32_t tsStreamNotifyFrameSize;
 extern int32_t tsStreamBatchRequestWaitMs;
 extern bool    tsCompareAsStrInGreatest;
+extern bool    tsIgnoreNullInGreatest;
 extern bool    tsShowFullCreateTableColumn;  // 0: show create table, and not include column compress info
 extern int32_t tsRpcRecvLogThreshold;        // in seconds, default 3
 

source/common/src/tglobal.c

@@ -217,6 +217,7 @@ int8_t   tsFlexDeploy = 0;
 #endif
 
 bool tsCompareAsStrInGreatest = true;
+bool tsIgnoreNullInGreatest = false;
 
 // monitor
 #ifdef USE_MONITOR
@@ -808,6 +809,9 @@ static int32_t taosAddClientCfg(SConfig *pCfg) {
   TAOS_CHECK_RETURN(cfgAddBool(pCfg, "compareAsStrInGreatest", tsCompareAsStrInGreatest, CFG_SCOPE_CLIENT,
                                CFG_DYN_CLIENT, CFG_CATEGORY_LOCAL, CFG_PRIV_SYSTEM));
 
+  TAOS_CHECK_RETURN(cfgAddBool(pCfg, "ignoreNullInGreatest", tsIgnoreNullInGreatest, CFG_SCOPE_CLIENT,
+                               CFG_DYN_CLIENT, CFG_CATEGORY_LOCAL, CFG_PRIV_SYSTEM));
+
   TAOS_CHECK_RETURN(cfgAddBool(pCfg, "showFullCreateTableColumn", tsShowFullCreateTableColumn, CFG_SCOPE_CLIENT,
                                CFG_DYN_CLIENT, CFG_CATEGORY_LOCAL, CFG_PRIV_SYSTEM));
 
@@ -1685,6 +1689,9 @@ static int32_t taosSetClientCfg(SConfig *pCfg) {
   TAOS_CHECK_GET_CFG_ITEM(pCfg, pItem, "compareAsStrInGreatest");
   tsCompareAsStrInGreatest = pItem->bval;
 
+  TAOS_CHECK_GET_CFG_ITEM(pCfg, pItem, "ignoreNullInGreatest");
+  tsIgnoreNullInGreatest = pItem->bval;
+
   TAOS_CHECK_GET_CFG_ITEM(pCfg, pItem, "showFullCreateTableColumn");
   tsShowFullCreateTableColumn = pItem->bval;
 
@@ -3387,6 +3394,7 @@ static int32_t taosCfgDynamicOptionsForClient(SConfig *pCfg, const char *name) {
                                          {"bypassFlag", &tsBypassFlag},
                                          {"safetyCheckLevel", &tsSafetyCheckLevel},
                                          {"compareAsStrInGreatest", &tsCompareAsStrInGreatest},
+                                         {"ignoreNullInGreatest", &tsIgnoreNullInGreatest},
                                          {"showFullCreateTableColumn", &tsShowFullCreateTableColumn}};
 
     if ((code = taosCfgSetOption(debugOptions, tListLen(debugOptions), pItem, true)) != TSDB_CODE_SUCCESS) {

source/libs/function/src/builtins.c

@@ -2208,13 +2208,21 @@ static int32_t translateGreatestleast(SFunctionNode* pFunc, char* pErrBuf, int32
   FUNC_ERR_RET(validateParam(pFunc, pErrBuf, len));
 
   bool mixTypeToStrings = tsCompareAsStrInGreatest;
+  bool ignoreNull = tsIgnoreNullInGreatest;
 
   SDataType res = {.type = 0};
   bool      resInit = false;
+  int32_t   nullLitCount = 0;
   for (int32_t i = 0; i < LIST_LENGTH(pFunc->pParameterList); i++) {
     SDataType* para = getSDataTypeFromNode(nodesListGetNode(pFunc->pParameterList, i));
 
     if (IS_NULL_TYPE(para->type)) {
+      if (ignoreNull) {
+        // Skip NULL literal params from result-type derivation; they are also
+        // ignored at runtime in greatestLeastImpl/vectorCompareAndSelect.
+        nullLitCount++;
+        continue;
+      }
       res.type = TSDB_DATA_TYPE_NULL;
       res.bytes = tDataTypes[TSDB_DATA_TYPE_NULL].bytes;
       break;
@@ -2255,7 +2263,20 @@ static int32_t translateGreatestleast(SFunctionNode* pFunc, char* pErrBuf, int32
       }
     }
   }
+  // ignoreNullInGreatest=1: if every param was a NULL literal the output is
+  // still NULL type (matches default behavior; FS §4.5).
+  if (ignoreNull && !resInit && nullLitCount > 0) {
+    res.type = TSDB_DATA_TYPE_NULL;
+    res.bytes = tDataTypes[TSDB_DATA_TYPE_NULL].bytes;
+  }
   pFunc->node.resType = res;
+
+  // tsIgnoreNullInGreatest is a CFG_SCOPE_CLIENT flag, so the runtime
+  // (which executes per-vnode) must receive its value via the param list.
+  // The flag is appended as a trailing TINYINT and stripped at runtime by
+  // greatestLeastImpl.  Mirrors the addUint8Param pattern used by trim,
+  // translateDate, and similar builtins.
+  FUNC_ERR_RET(addUint8Param(&pFunc->pParameterList, ignoreNull ? 1 : 0));
   return TSDB_CODE_SUCCESS;
 }