planner: don't prune sleep function in LogicalProjection （pingcap#11927…

…） (pingcap#13198)

cmd/explaintest/r/select.result

@@ -443,3 +443,8 @@ Projection_8	10000.00	root	minus(4_window_3, test.t.x)
   └─Sort_12	10000.00	root	test.t.i:asc
     └─TableReader_11	10000.00	root	data:TableScan_10
       └─TableScan_10	10000.00	cop	table:t, range:[0,+inf], keep order:false, stats:pseudo
+explain select 1 from (select sleep(1)) t;
+id	count	task	operator info
+Projection_4	1.00	root	1
+└─Projection_5	1.00	root	sleep(1)
+  └─TableDual_6	1.00	root	rows:1

cmd/explaintest/t/select.test

@@ -210,3 +210,5 @@ CREATE TABLE t (id int(10) unsigned NOT NULL AUTO_INCREMENT,
     PRIMARY KEY (`id`)
 );
 explain select row_number() over( partition by i ) - x as rnk from t;
+
+explain select 1 from (select sleep(1)) t;

planner/core/rule_column_pruning.go

@@ -53,25 +53,25 @@ func getUsedList(usedCols []*expression.Column, schema *expression.Schema) ([]bo
 	return used, nil
 }
 
-// exprHasSetVar checks if the expression has SetVar function.
-func exprHasSetVar(expr expression.Expression) bool {
+// exprHasSetVarOrSleep checks if the expression has SetVar function or Sleep function.
+func exprHasSetVarOrSleep(expr expression.Expression) bool {
 	scalaFunc, isScalaFunc := expr.(*expression.ScalarFunction)
 	if !isScalaFunc {
 		return false
 	}
-	if scalaFunc.FuncName.L == ast.SetVar {
+	if scalaFunc.FuncName.L == ast.SetVar || scalaFunc.FuncName.L == ast.Sleep {
 		return true
 	}
 	for _, arg := range scalaFunc.GetArgs() {
-		if exprHasSetVar(arg) {
+		if exprHasSetVarOrSleep(arg) {
 			return true
 		}
 	}
 	return false
 }
 
 // PruneColumns implements LogicalPlan interface.
-// If any expression has SetVar functions, we do not prune it.
+// If any expression has SetVar function or Sleep function, we do not prune it.
 func (p *LogicalProjection) PruneColumns(parentUsedCols []*expression.Column) error {
 	child := p.children[0]
 	used, err := getUsedList(parentUsedCols, p.schema)
@@ -80,7 +80,7 @@ func (p *LogicalProjection) PruneColumns(parentUsedCols []*expression.Column) er
 	}
 
 	for i := len(used) - 1; i >= 0; i-- {
-		if !used[i] && !exprHasSetVar(p.Exprs[i]) {
+		if !used[i] && !exprHasSetVarOrSleep(p.Exprs[i]) {
 			p.schema.Columns = append(p.schema.Columns[:i], p.schema.Columns[i+1:]...)
 			p.Exprs = append(p.Exprs[:i], p.Exprs[i+1:]...)
 		}