sql: fix table sample sql generator bug (#262)

go.mod

@@ -22,6 +22,7 @@ require (
 	github.com/pingcap/tidb-tools v4.0.9-0.20201127090955-2707c97b3853+incompatible
 	github.com/prometheus/client_golang v1.5.1
 	github.com/prometheus/client_model v0.2.0
+	github.com/siddontang/go-mysql v0.0.0-20200222075837-12e89848f047
 	github.com/soheilhy/cmux v0.1.4
 	github.com/spf13/pflag v1.0.5
 	github.com/syndtr/goleveldb v1.0.1-0.20190625010220-02440ea7a285 // indirect

go.sum

@@ -766,6 +766,7 @@ github.com/russross/blackfriday v1.5.2/go.mod h1:JO/DiYxRf+HjHt06OyowR9PTA263kcR
 github.com/russross/blackfriday/v2 v2.0.1/go.mod h1:+Rmxgy9KzJVeS9/2gXHxylqXiyQDYRxCVz55jmeOWTM=
 github.com/sasha-s/go-deadlock v0.2.0/go.mod h1:StQn567HiB1fF2yJ44N9au7wOhrPS3iZqiDbRupzT10=
 github.com/satori/go.uuid v1.2.0/go.mod h1:dA0hQrYB0VpLJoorglMZABFdXlWrHn1NEOzdhQKdks0=
+github.com/satori/go.uuid v1.2.1-0.20181028125025-b2ce2384e17b h1:gQZ0qzfKHQIybLANtM3mBXNUtOfsCFXeTsnBqCsx1KM=
 github.com/satori/go.uuid v1.2.1-0.20181028125025-b2ce2384e17b/go.mod h1:dA0hQrYB0VpLJoorglMZABFdXlWrHn1NEOzdhQKdks0=
 github.com/segmentio/kafka-go v0.1.0/go.mod h1:X6itGqS9L4jDletMsxZ7Dz+JFWxM6JHfPOCvTvk+EJo=
 github.com/segmentio/kafka-go v0.2.0/go.mod h1:X6itGqS9L4jDletMsxZ7Dz+JFWxM6JHfPOCvTvk+EJo=
@@ -789,9 +790,12 @@ github.com/shurcooL/sanitized_anchor_name v1.0.0/go.mod h1:1NzhyTcUVG4SuEtjjoZeV
 github.com/shurcooL/vfsgen v0.0.0-20181020040650-a97a25d856ca/go.mod h1:TrYk7fJVaAttu97ZZKrO9UbRa8izdowaMIZcxYMbVaw=
 github.com/shurcooL/vfsgen v0.0.0-20181202132449-6a9ea43bcacd h1:ug7PpSOB5RBPK1Kg6qskGBoP3Vnj/aNYFTznWvlkGo0=
 github.com/shurcooL/vfsgen v0.0.0-20181202132449-6a9ea43bcacd/go.mod h1:TrYk7fJVaAttu97ZZKrO9UbRa8izdowaMIZcxYMbVaw=
+github.com/siddontang/go v0.0.0-20180604090527-bdc77568d726 h1:xT+JlYxNGqyT+XcU8iUrN18JYed2TvG9yN5ULG2jATM=
 github.com/siddontang/go v0.0.0-20180604090527-bdc77568d726/go.mod h1:3yhqj7WBBfRhbBlzyOC3gUxftwsU0u8gqevxwIHQpMw=
 github.com/siddontang/go-log v0.0.0-20180807004314-8d05993dda07/go.mod h1:yFdBgwXP24JziuRl2NMUahT7nGLNOKi1SIiFxMttVD4=
+github.com/siddontang/go-log v0.0.0-20190221022429-1e957dd83bed h1:KMgQoLJGCq1IoZpLZE3AIffh9veYWoVlsvA4ib55TMM=
 github.com/siddontang/go-log v0.0.0-20190221022429-1e957dd83bed/go.mod h1:yFdBgwXP24JziuRl2NMUahT7nGLNOKi1SIiFxMttVD4=
+github.com/siddontang/go-mysql v0.0.0-20200222075837-12e89848f047 h1:boyJ8EgQN/aC3grvx8QUoJrptt7RvneezSJSCbW25a4=
 github.com/siddontang/go-mysql v0.0.0-20200222075837-12e89848f047/go.mod h1:+W4RCzesQDI11HvIkaDjS8yM36SpAnGNQ7jmTLn5BnU=
 github.com/sirupsen/logrus v1.2.0/go.mod h1:LxeOpSwHxABJmUn/MG1IvRgCAasNZTLOkJPxbbu5VWo=
 github.com/sirupsen/logrus v1.3.0/go.mod h1:LxeOpSwHxABJmUn/MG1IvRgCAasNZTLOkJPxbbu5VWo=

v4/export/dump.go

@@ -616,6 +616,9 @@ func selectTiDBTableSample(conn *sql.Conn, dbName, tableName string) (pkFields [
 	if hasImplicitRowID {
 		pkFields, pkColTypes = []string{"_tidb_rowid"}, []string{"BIGINT"}
 	}
+	if len(pkFields) == 0 {
+		return pkFields, pkVals, nil
+	}
 	query := buildTiDBTableSampleQuery(pkFields, dbName, tableName)
 	rows, err := conn.QueryContext(context.Background(), query)
 	if err != nil {
@@ -638,7 +641,6 @@ func selectTiDBTableSample(conn *sql.Conn, dbName, tableName string) (pkFields [
 			pkValRow = append(pkValRow, buf.String())
 			buf.Reset()
 		}
-		rowRec.WriteToBuffer(buf, true)
 		pkVals = append(pkVals, pkValRow)
 		iter.Next()
 	}

v4/export/dump_test.go

@@ -25,7 +25,7 @@ func (s *testSQLSuite) TestDumpBlock(c *C) {
 		WillReturnRows(sqlmock.NewRows([]string{"Database", "Create Database"}).
 			AddRow("test", "CREATE DATABASE `test` /*!40100 DEFAULT CHARACTER SET utf8mb4 */"))
 
-	tctx, cancel := tcontext.Background().WithCancel()
+	tctx, cancel := tcontext.Background().WithLogger(appLogger).WithCancel()
 	defer cancel()
 	conn, err := db.Conn(tctx)
 	c.Assert(err, IsNil)

v4/export/sql.go

@@ -675,26 +675,14 @@ func buildCompareClause(buf *bytes.Buffer, quotaCols []string, bound []string, c
 	}
 }
 
-// Compare returns an integer comparing two string arrays lexicographically.
-// return (compare result, common prefix length)
-// return -1 if low < up
-// return  0 if low == up
-// return  1 if low > up
-func compareArrString(low []string, up []string) (compareRes, commonLength int) {
-	l := len(low)
-	c := -1
-	if u := len(up); u < l {
-		l = u
-		c = 1
-	} else if u == l {
-		c = 0
-	}
-	for i := 0; i < l; i++ {
-		if d := strings.Compare(low[i], up[i]); d != 0 {
-			return d, i
+// getCommonLength returns the common length of low and up
+func getCommonLength(low []string, up []string) int {
+	for i := range low {
+		if low[i] != up[i] {
+			return i
 		}
 	}
-	return c, l
+	return len(low)
 }
 
 // buildBetweenClause build clause in a specified table range.
@@ -713,13 +701,13 @@ func buildBetweenClause(buf *bytes.Buffer, quotaCols []string, low []string, up
 		buf.WriteString(up[0])
 	}
 	// handle special cases with common prefix
-	compare, commonLen := compareArrString(low, up)
-	// unexpected case for low >= up, return empty result
-	if compare >= 0 {
-		buf.WriteString("false")
-		return
-	}
+	commonLen := getCommonLength(low, up)
 	if commonLen > 0 {
+		// unexpected case for low == up, return empty result
+		if commonLen == len(low) {
+			buf.WriteString("false")
+			return
+		}
 		for i := 0; i < commonLen; i++ {
 			if i > 0 {
 				buf.WriteString(" and ")