planner: The length function could not be substitute when collation o…

…f mapped column is utfxxx_bin (#54179) (#56994)

close #53730

expression/constant_propagation.go

@@ -358,6 +358,11 @@ func (s *propConstSolver) solve(conditions []Expression) []Expression {
 
 // PropagateConstant propagate constant values of deterministic predicates in a condition.
 func PropagateConstant(ctx sessionctx.Context, conditions []Expression) []Expression {
+	sc := ctx.GetSessionVars().StmtCtx
+	sc.InConstantPropagateCheck = true
+	defer func() {
+		sc.InConstantPropagateCheck = false
+	}()
 	return newPropConstSolver().PropagateConstant(ctx, conditions)
 }
 

expression/util.go

@@ -27,6 +27,7 @@ import (
 	"github.com/pingcap/failpoint"
 	"github.com/pingcap/tidb/kv"
 	"github.com/pingcap/tidb/parser/ast"
+	"github.com/pingcap/tidb/parser/charset"
 	"github.com/pingcap/tidb/parser/mysql"
 	"github.com/pingcap/tidb/parser/opcode"
 	"github.com/pingcap/tidb/parser/terror"
@@ -461,6 +462,28 @@ func ColumnSubstituteImpl(expr Expression, schema *Schema, newExprs []Expression
 			}
 			return false, false, v
 		}
+		// If the collation of the column is PAD SPACE,
+		// we can't propagate the constant to the length function.
+		// For example, schema = ['name'], newExprs = ['a'], v = length(name).
+		// We can't substitute name with 'a' in length(name) because the collation of name is PAD SPACE.
+		// TODO: We will fix it here temporarily, and redesign the logic if we encounter more similar functions or situations later.
+		// Fixed issue #53730
+		if v.GetCtx().GetSessionVars().StmtCtx.InConstantPropagateCheck && v.FuncName.L == ast.Length {
+			arg0, isColumn := v.GetArgs()[0].(*Column)
+			if isColumn {
+				id := schema.ColumnIndex(arg0)
+				if id != -1 {
+					_, isConstant := newExprs[id].(*Constant)
+					if isConstant {
+						mappedNewColumnCollate := schema.Columns[id].GetType().GetCollate()
+						if mappedNewColumnCollate == charset.CollationUTF8MB4 ||
+							mappedNewColumnCollate == charset.CollationUTF8 {
+							return false, false, v
+						}
+					}
+				}
+			}
+		}
 		// cowExprRef is a copy-on-write util, args array allocation happens only
 		// when expr in args is changed
 		refExprArr := cowExprRef{v.GetArgs(), nil}

planner/core/casetest/main_test.go

@@ -138,3 +138,7 @@ func GetDerivedTopNSuiteData() testdata.TestData {
 func GetPredicateSimplificationTestData() testdata.TestData {
 	return testDataMap["predicate_simplification"]
 }
+
+func GetPredicatePushdownSuiteData() testdata.TestData {
+	return testDataMap["predicate_pushdown_suite"]
+}

planner/core/casetest/physical_plan_test.go

@@ -2562,3 +2562,34 @@ func TestIndexMergeOrderPushDown(t *testing.T) {
 		tk.MustQuery("show warnings").Check(testkit.Rows(output[i].Warning...))
 	}
 }
+
+func TestConstantPropagateWithCollation(t *testing.T) {
+	var input []string
+	var output []struct {
+		SQL     string
+		Plan    []string
+		Warning []string
+	}
+	planSuiteData := GetPlanSuiteData()
+	planSuiteData.LoadTestCases(t, &input, &output)
+	store := testkit.CreateMockStore(t)
+	tk := testkit.NewTestKit(t, store)
+	// create table
+	tk.MustExec("use test")
+	tk.MustExec("create table t (id int primary key, name varchar(20));")
+	require.Equal(t, len(input), len(output))
+
+	for i := range input {
+		if strings.Contains(input[i], "set") {
+			tk.MustExec(input[i])
+			continue
+		}
+		testdata.OnRecord(func() {
+			output[i].SQL = input[i]
+			output[i].Plan = testdata.ConvertRowsToStrings(tk.MustQuery("explain format = 'brief' " + input[i]).Rows())
+			output[i].Warning = testdata.ConvertRowsToStrings(tk.MustQuery("show warnings").Rows())
+		})
+		tk.MustQuery("explain format = 'brief' " + input[i]).Check(testkit.Rows(output[i].Plan...))
+		tk.MustQuery("show warnings").Check(testkit.Rows(output[i].Warning...))
+	}
+}

planner/core/casetest/testdata/plan_suite_in.json

@@ -1351,5 +1351,15 @@
       "select * from employee where dept_id = 1 union all ( select * from employee where dept_id = 1 order by employee_id) union all ( select * from employee where dept_id = 1 union all ( select * from employee where dept_id = 1 order by employee_id ) limit 1);",
       "select * from employee where dept_id = 1 union all ( select * from employee where dept_id = 1 order by employee_id) union all ( select * from employee where dept_id = 1 union all ( select * from employee where dept_id = 1 order by employee_id ) order by 1 limit 1);"
     ]
+  },
+  {
+    "name": "TestConstantPropagateWithCollation",
+    "cases": [
+      "set names utf8",
+      "select * from t where name='a' and length(name)=1; -- without constant propagated",
+      "set names utf8mb4",
+      "select * from t where name='a' and length(name)=1; -- without constant propagated",
+      "select * from (select 'test' as b from t) n where length(b) > 2; -- can be substituted"
+    ]
   }
 ]

planner/core/casetest/testdata/plan_suite_out.json

@@ -8951,5 +8951,47 @@
         "Warning": null
       }
     ]
+  },
+  {
+    "Name": "TestConstantPropagateWithCollation",
+    "Cases": [
+      {
+        "SQL": "",
+        "Plan": null,
+        "Warning": null
+      },
+      {
+        "SQL": "select * from t where name='a' and length(name)=1; -- without constant propagated",
+        "Plan": [
+          "TableReader 8.00 root  data:Selection",
+          "└─Selection 8.00 cop[tikv]  eq(length(test.t.name), 1), eq(test.t.name, \"a\")",
+          "  └─TableFullScan 10000.00 cop[tikv] table:t keep order:false, stats:pseudo"
+        ],
+        "Warning": null
+      },
+      {
+        "SQL": "",
+        "Plan": null,
+        "Warning": null
+      },
+      {
+        "SQL": "select * from t where name='a' and length(name)=1; -- without constant propagated",
+        "Plan": [
+          "TableReader 8.00 root  data:Selection",
+          "└─Selection 8.00 cop[tikv]  eq(length(test.t.name), 1), eq(test.t.name, \"a\")",
+          "  └─TableFullScan 10000.00 cop[tikv] table:t keep order:false, stats:pseudo"
+        ],
+        "Warning": null
+      },
+      {
+        "SQL": "select * from (select 'test' as b from t) n where length(b) > 2; -- can be substituted",
+        "Plan": [
+          "Projection 10000.00 root  test->Column#3",
+          "└─TableReader 10000.00 root  data:TableFullScan",
+          "  └─TableFullScan 10000.00 cop[tikv] table:t keep order:false, stats:pseudo"
+        ],
+        "Warning": null
+      }
+    ]
   }
 ]

sessionctx/stmtctx/stmtctx.go

@@ -178,6 +178,7 @@ type StatementContext struct {
 	CacheType                     PlanCacheType
 	BatchCheck                    bool
 	InNullRejectCheck             bool
+	InConstantPropagateCheck      bool
 	AllowInvalidDate              bool
 	IgnoreNoPartition             bool
 	IgnoreExplainIDSuffix         bool