From 0bca04440ff1d01f864670c9e8b82368142aabbd Mon Sep 17 00:00:00 2001
From: yihaoDeng <yhdeng@taosdata.com>
Date: Thu, 14 Jan 2021 12:56:03 +0000
Subject: [PATCH] TD-2571

---
 src/client/inc/tsclient.h      |  2 ++
 src/client/src/tscLocalMerge.c |  4 ++--
 src/client/src/tscSQLParser.c  | 33 +++++++++++++++++++++++++++++++--
 3 files changed, 35 insertions(+), 4 deletions(-)

diff --git a/src/client/inc/tsclient.h b/src/client/inc/tsclient.h
index 900fab53a2..26a2502106 100644
--- a/src/client/inc/tsclient.h
+++ b/src/client/inc/tsclient.h
@@ -223,6 +223,8 @@ typedef struct SQueryInfo {
 
   int32_t          udColumnId;    // current user-defined constant output field column id, monotonically decreases from TSDB_UD_COLUMN_INDEX
   int16_t          resColumnId;   // result column id
+  bool             distinctTag;   // distinct tag or not
+  
 } SQueryInfo;
 
 typedef struct {
diff --git a/src/client/src/tscLocalMerge.c b/src/client/src/tscLocalMerge.c
index 4aa751574c..80dde8576f 100644
--- a/src/client/src/tscLocalMerge.c
+++ b/src/client/src/tscLocalMerge.c
@@ -1102,7 +1102,7 @@ static int64_t getNumOfResultLocal(SQueryInfo *pQueryInfo, SQLFunctionCtx *pCtx)
      * the number of output result is decided by main output
      */
     int32_t functionId = pCtx[j].functionId;
-    if (functionId == TSDB_FUNC_TS || functionId == TSDB_FUNC_TAG || functionId == TSDB_FUNC_TAGPRJ) {
+    if (functionId == TSDB_FUNC_TS || functionId == TSDB_FUNC_TAG) {
       continue;
     }
 
@@ -1184,7 +1184,7 @@ bool needToMerge(SQueryInfo *pQueryInfo, SLocalReducer *pLocalReducer, tFilePage
   int16_t functionId = pLocalReducer->pCtx[0].functionId;
 
   // todo opt performance
-  if ((/*functionId == TSDB_FUNC_PRJ || */functionId == TSDB_FUNC_ARITHM) || (tscIsProjectionQueryOnSTable(pQueryInfo, 0))) {  // column projection query
+  if ((/*functionId == TSDB_FUNC_PRJ || */functionId == TSDB_FUNC_ARITHM) || (tscIsProjectionQueryOnSTable(pQueryInfo, 0) && pQueryInfo->distinctTag == false)) {  // column projection query
     ret = 1;                                                            // disable merge procedure
   } else {
     tOrderDescriptor *pDesc = pLocalReducer->pDesc;
diff --git a/src/client/src/tscSQLParser.c b/src/client/src/tscSQLParser.c
index ffb2927cbd..94b01f0a65 100644
--- a/src/client/src/tscSQLParser.c
+++ b/src/client/src/tscSQLParser.c
@@ -1476,23 +1476,39 @@ static void addPrimaryTsColIntoResult(SQueryInfo* pQueryInfo) {
   pQueryInfo->type |= TSDB_QUERY_TYPE_PROJECTION_QUERY;
 }
 
+bool isValidDistinctSql(SQueryInfo* pQueryInfo) {
+  if (pQueryInfo == NULL) {
+    return false;
+  }
+  if ((pQueryInfo->type & TSDB_QUERY_TYPE_STABLE_QUERY)  != TSDB_QUERY_TYPE_STABLE_QUERY) {
+    return false;
+  }
+  if (tscQueryTags(pQueryInfo) && tscSqlExprNumOfExprs(pQueryInfo) == 1){
+    return true;
+  }
+  return false;
+}
 int32_t parseSelectClause(SSqlCmd* pCmd, int32_t clauseIndex, tSQLExprList* pSelection, bool isSTable, bool joinQuery, bool intervalQuery) {
   assert(pSelection != NULL && pCmd != NULL);
 
   const char* msg2 = "functions can not be mixed up";
   const char* msg3 = "not support query expression";
   const char* msg5 = "invalid function name";
+  const char* msg6 = "only support distinct one tag";
 
   SQueryInfo* pQueryInfo = tscGetQueryInfoDetail(pCmd, clauseIndex);
 
   if (pQueryInfo->colList == NULL) {
     pQueryInfo->colList = taosArrayInit(4, POINTER_BYTES);
   }
-
+  bool hasDistinct = false;
   for (int32_t i = 0; i < pSelection->nExpr; ++i) {
     int32_t outputIndex = (int32_t)tscSqlExprNumOfExprs(pQueryInfo);
     tSqlExprItem* pItem = &pSelection->a[i];
-
+     
+    if (hasDistinct == false) {
+       hasDistinct = (pItem->distinct == true); 
+    }
     // project on all fields
     int32_t optr = pItem->pNode->nSQLOptr;
 
@@ -1526,6 +1542,13 @@ int32_t parseSelectClause(SSqlCmd* pCmd, int32_t clauseIndex, tSQLExprList* pSel
     }
   }
 
+  if (hasDistinct == true) {
+    if (!isValidDistinctSql(pQueryInfo)) {
+      return invalidSqlErrMsg(tscGetErrorMsgPayload(pCmd), msg6);
+    }
+    pQueryInfo->distinctTag = true;
+  }
+  
   // there is only one user-defined column in the final result field, add the timestamp column.
   size_t numOfSrcCols = taosArrayGetSize(pQueryInfo->colList);
   if (numOfSrcCols <= 0 && !tscQueryTags(pQueryInfo)) {
@@ -4605,6 +4628,12 @@ int32_t parseOrderbyClause(SSqlCmd* pCmd, SQueryInfo* pQueryInfo, SQuerySQL* pQu
   setDefaultOrderInfo(pQueryInfo);
   STableMetaInfo* pTableMetaInfo = tscGetMetaInfo(pQueryInfo, 0);
 
+
+  if (pQueryInfo->distinctTag == true) {
+    pQueryInfo->order.order = TSDB_ORDER_ASC;
+    pQueryInfo->order.orderColId = 0; 
+    return TSDB_CODE_SUCCESS;
+  }
   if (pQuerySql->pSortOrder == NULL) {
     return TSDB_CODE_SUCCESS;
   }
-- 
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