From 3f3ead2d594507a24e1e86b8318463f3352fac16 Mon Sep 17 00:00:00 2001
From: miraclesu <suchuangji@gmail.com>
Date: Mon, 5 Aug 2019 06:14:11 -0500
Subject: [PATCH] executor: fix #10513, alias identifier maximum length
 compatible with MySQL (#10597)

---
 executor/adapter.go |  9 +++++++++
 server/tidb_test.go | 16 ++++++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/executor/adapter.go b/executor/adapter.go
index a7c63c854d081..cf61065498f1c 100644
--- a/executor/adapter.go
+++ b/executor/adapter.go
@@ -90,6 +90,15 @@ func schema2ResultFields(schema *expression.Schema, defaultDB string) (rfs []*as
 				Name:      origColName,
 			},
 		}
+		// This is for compatibility.
+		if len(rf.ColumnAsName.O) > mysql.MaxAliasIdentifierLen {
+			rf.ColumnAsName.O = rf.ColumnAsName.O[:mysql.MaxAliasIdentifierLen]
+		}
+		// Usually the length of O equals the length of L.
+		// Add this len judgement to avoid panic.
+		if len(rf.ColumnAsName.L) > mysql.MaxAliasIdentifierLen {
+			rf.ColumnAsName.L = rf.ColumnAsName.L[:mysql.MaxAliasIdentifierLen]
+		}
 		rfs = append(rfs, rf)
 	}
 	return rfs
diff --git a/server/tidb_test.go b/server/tidb_test.go
index 84bb7c5921055..cf7677c46473c 100644
--- a/server/tidb_test.go
+++ b/server/tidb_test.go
@@ -544,6 +544,22 @@ func (ts *TidbTestSuite) TestFieldList(c *C) {
 
 	// c_decimal decimal(6, 3)
 	c.Assert(colInfos[5].Decimal, Equals, uint8(3))
+
+	// for issue#10513
+	tooLongColumnAsName := "COALESCE(0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0)"
+	columnAsName := tooLongColumnAsName[:tmysql.MaxAliasIdentifierLen]
+
+	rs, err := qctx.Execute(ctx, "select "+tooLongColumnAsName)
+	c.Assert(err, IsNil)
+	cols := rs[0].Columns()
+	c.Assert(cols[0].OrgName, Equals, tooLongColumnAsName)
+	c.Assert(cols[0].Name, Equals, columnAsName)
+
+	rs, err = qctx.Execute(ctx, "select c_bit as '"+tooLongColumnAsName+"' from t")
+	c.Assert(err, IsNil)
+	cols = rs[0].Columns()
+	c.Assert(cols[0].OrgName, Equals, "c_bit")
+	c.Assert(cols[0].Name, Equals, columnAsName)
 }
 
 func (ts *TidbTestSuite) TestSumAvg(c *C) {