planner: add warning when use_index_merge hint's index names are invalid

planner/core/integration_test.go

@@ -704,8 +704,8 @@ func (s *testIntegrationSuite) TestIndexHintWarning(c *C) {
 	tk := testkit.NewTestKit(c, s.store)
 	tk.MustExec("use test")
 	tk.MustExec("drop table if exists t1, t2")
-	tk.MustExec("create table t1(a int, b int, c int, key a(a))")
-	tk.MustExec("create table t2(a int, b int, c int, key a(a))")
+	tk.MustExec("create table t1(a int, b int, c int, key a(a), key b(b))")
+	tk.MustExec("create table t2(a int, b int, c int, key a(a), key b(b))")
 	var input []string
 	var output []struct {
 		SQL      string

planner/core/logical_plan_builder.go

@@ -2689,8 +2689,37 @@ func (b *PlanBuilder) buildDataSource(ctx context.Context, tn *ast.TableName, as
 	if hints := b.TableHints(); hints != nil {
 		for i, hint := range hints.indexMergeHintList {
 			if hint.tblName.L == tblName.L {
-				indexMergeHints = append(indexMergeHints, hint.indexHint)
 				hints.indexMergeHintList[i].matched = true
+				// check whether the index names in IndexMergeHint are valid.
+				invalidIdxNames := make([]string, 0, len(hint.indexHint.IndexNames))
+				for _, idxName := range hint.indexHint.IndexNames {
+					hasIdxName := false
+					for _, path := range possiblePaths {
+						if path.IsTablePath {
+							if idxName.L == "primary" {
+								hasIdxName = true
+								break
+							}
+							continue
+						}
+						if idxName.L == path.Index.Name.L {
+							hasIdxName = true
+							break
+						}
+					}
+					if !hasIdxName {
+						invalidIdxNames = append(invalidIdxNames, idxName.String())
+					}
+				}
+				if len(invalidIdxNames) == 0 {
+					indexMergeHints = append(indexMergeHints, hint.indexHint)
+				} else {
+					// Append warning if there are invalid index names.
+					errMsg := fmt.Sprintf("use_index_merge(%s) is inapplicable, check whether the indexes (%s) "+
+						"exist, or the indexes are conflicted with use_index/ignore_index hints.",
+						hint.indexString(), strings.Join(invalidIdxNames, ", "))
+					b.ctx.GetSessionVars().StmtCtx.AppendWarning(ErrInternal.GenWithStack(errMsg))
+				}
 			}
 		}
 	}

planner/core/testdata/integration_suite_in.json

@@ -80,7 +80,11 @@
       "select /*+ USE_INDEX(t2) */ * from t1",
       "select /*+ USE_INDEX(t1, a), USE_INDEX(t2, a), USE_INDEX(t3, a) */ * from t1, t2 where t1.a=t2.a",
       "select /*+ USE_INDEX(t3, a), USE_INDEX(t4, b), IGNORE_INDEX(t3, a) */ * from t1, t2 where t1.a=t2.a",
-      "select /*+ USE_INDEX_MERGE(t3, a, b, d) */ * from t1"
+      "select /*+ USE_INDEX_MERGE(t3, a, b, d) */ * from t1",
+      "select /*+ USE_INDEX_MERGE(t1, a, b, c, d) */ * from t1",
+      "select /*+ USE_INDEX_MERGE(t1, a, b), USE_INDEX(t1, a) */ * from t1",
+      "select /*+ USE_INDEX_MERGE(t1, a, b), IGNORE_INDEX(t1, a) */ * from t1",
+      "select /*+ USE_INDEX_MERGE(t1, primary, a, b, c) */ * from t1"
     ]
   },
   {

planner/core/testdata/integration_suite_out.json

@@ -301,6 +301,30 @@
         "Warnings": [
           "[planner:1815]use_index_merge(test.t3, a, b, d) is inapplicable, check whether the table(test.t3) exists"
         ]
+      },
+      {
+        "SQL": "select /*+ USE_INDEX_MERGE(t1, a, b, c, d) */ * from t1",
+        "Warnings": [
+          "[planner:1815]use_index_merge(test.t1, a, b, c, d) is inapplicable, check whether the indexes (c, d) exist, or the indexes are conflicted with use_index/ignore_index hints."
+        ]
+      },
+      {
+        "SQL": "select /*+ USE_INDEX_MERGE(t1, a, b), USE_INDEX(t1, a) */ * from t1",
+        "Warnings": [
+          "[planner:1815]use_index_merge(test.t1, a, b) is inapplicable, check whether the indexes (b) exist, or the indexes are conflicted with use_index/ignore_index hints."
+        ]
+      },
+      {
+        "SQL": "select /*+ USE_INDEX_MERGE(t1, a, b), IGNORE_INDEX(t1, a) */ * from t1",
+        "Warnings": [
+          "[planner:1815]use_index_merge(test.t1, a, b) is inapplicable, check whether the indexes (a) exist, or the indexes are conflicted with use_index/ignore_index hints."
+        ]
+      },
+      {
+        "SQL": "select /*+ USE_INDEX_MERGE(t1, primary, a, b, c) */ * from t1",
+        "Warnings": [
+          "[planner:1815]use_index_merge(test.t1, primary, a, b, c) is inapplicable, check whether the indexes (c) exist, or the indexes are conflicted with use_index/ignore_index hints."
+        ]
       }
     ]
   },