Add support for returning table alias on Columns().

Currently the driver discards the column alias and the original table
name. This change adds a new configuration parameter to include the
table alias with the column name.

This is useful because when mapping columns to structs, it is impossible
to distinguish between duplicate column names when doing JOIN queries.

Author: chrismoos

AUTHORS

@@ -14,6 +14,7 @@
 Aaron Hopkins <go-sql-driver at die.net>
 Arne Hormann <arnehormann at gmail.com>
 Carlos Nieto <jose.carlos at menteslibres.net>
+Chris Moos <chris at tech9computers.com>
 DisposaBoy <disposaboy at dby.me>
 Frederick Mayle <frederickmayle at gmail.com>
 Gustavo Kristic <gkristic at gmail.com>

README.md

@@ -166,6 +166,21 @@ Default:        false
 
 `clientFoundRows=true` causes an UPDATE to return the number of matching rows instead of the number of rows changed.
 
+##### `columnsWithAlias`
+
+```
+Type:           bool
+Valid Values:   true, false
+Default:        false
+```
+
+When `columnsWithAlias` is true, calls to `sql.Rows.Columns()` will return the table alias and the column name separated by a dot. For example:
+
+```
+SELECT u.id FROM users as u
+```
+
+will return `u.id` instead of just `id` if `columnsWithAlias=true`.
 
 ##### `loc`
 

connection.go

@@ -45,6 +45,7 @@ type config struct {
 	allowAllFiles     bool
 	allowOldPasswords bool
 	clientFoundRows   bool
+	columnsWithAlias  bool
 }
 
 // Handles parameters set in DSN after the connection is established

packets.go

@@ -530,11 +530,20 @@ func (mc *mysqlConn) readColumns(count int) ([]mysqlField, error) {
 		pos += n
 
 		// Table [len coded string]
-		n, err = skipLengthEncodedString(data[pos:])
-		if err != nil {
-			return nil, err
+		if mc.cfg.columnsWithAlias {
+			tableName, _, n, err := readLengthEncodedString(data[pos:])
+			if err != nil {
+				return nil, err
+			}
+			pos += n
+			columns[i].tableName = string(tableName)
+		} else {
+			n, err = skipLengthEncodedString(data[pos:])
+			if err != nil {
+				return nil, err
+			}
+			pos += n
 		}
-		pos += n
 
 		// Original table [len coded string]
 		n, err = skipLengthEncodedString(data[pos:])

rows.go

@@ -14,6 +14,7 @@ import (
 )
 
 type mysqlField struct {
+	tableName string
 	name      string
 	flags     fieldFlag
 	fieldType byte
@@ -37,8 +38,14 @@ type emptyRows struct{}
 
 func (rows *mysqlRows) Columns() []string {
 	columns := make([]string, len(rows.columns))
-	for i := range columns {
-		columns[i] = rows.columns[i].name
+	if rows.mc.cfg.columnsWithAlias {
+		for i := range columns {
+			columns[i] = rows.columns[i].tableName + "." + rows.columns[i].name
+		}
+	} else {
+		for i := range columns {
+			columns[i] = rows.columns[i].name
+		}
 	}
 	return columns
 }

utils.go

@@ -215,6 +215,13 @@ func parseDSNParams(cfg *config, params string) (err error) {
 			}
 			cfg.collation = collation
 			break
+		
+		case "columnsWithAlias":
+			var isBool bool
+			cfg.columnsWithAlias, isBool = readBool(value)
+			if !isBool {
+				return fmt.Errorf("Invalid Bool value: %s", value)
+			}
 
 		// Time Location
 		case "loc":

utils_test.go

@@ -21,18 +21,19 @@ var testDSNs = []struct {
 	out string
 	loc *time.Location
 }{
-	{"username:password@protocol(address)/dbname?param=value", "&{user:username passwd:password net:protocol addr:address dbname:dbname params:map[param:value] loc:%p tls:<nil> timeout:0 collation:33 allowAllFiles:false allowOldPasswords:false clientFoundRows:false}", time.UTC},
-	{"user@unix(/path/to/socket)/dbname?charset=utf8", "&{user:user passwd: net:unix addr:/path/to/socket dbname:dbname params:map[charset:utf8] loc:%p tls:<nil> timeout:0 collation:33 allowAllFiles:false allowOldPasswords:false clientFoundRows:false}", time.UTC},
-	{"user:password@tcp(localhost:5555)/dbname?charset=utf8&tls=true", "&{user:user passwd:password net:tcp addr:localhost:5555 dbname:dbname params:map[charset:utf8] loc:%p tls:<nil> timeout:0 collation:33 allowAllFiles:false allowOldPasswords:false clientFoundRows:false}", time.UTC},
-	{"user:password@tcp(localhost:5555)/dbname?charset=utf8mb4,utf8&tls=skip-verify", "&{user:user passwd:password net:tcp addr:localhost:5555 dbname:dbname params:map[charset:utf8mb4,utf8] loc:%p tls:<nil> timeout:0 collation:33 allowAllFiles:false allowOldPasswords:false clientFoundRows:false}", time.UTC},
-	{"user:password@/dbname?loc=UTC&timeout=30s&allowAllFiles=1&clientFoundRows=true&allowOldPasswords=TRUE&collation=utf8mb4_unicode_ci", "&{user:user passwd:password net:tcp addr:127.0.0.1:3306 dbname:dbname params:map[] loc:%p tls:<nil> timeout:30000000000 collation:224 allowAllFiles:true allowOldPasswords:true clientFoundRows:true}", time.UTC},
-	{"user:p@ss(word)@tcp([de:ad:be:ef::ca:fe]:80)/dbname?loc=Local", "&{user:user passwd:p@ss(word) net:tcp addr:[de:ad:be:ef::ca:fe]:80 dbname:dbname params:map[] loc:%p tls:<nil> timeout:0 collation:33 allowAllFiles:false allowOldPasswords:false clientFoundRows:false}", time.Local},
-	{"/dbname", "&{user: passwd: net:tcp addr:127.0.0.1:3306 dbname:dbname params:map[] loc:%p tls:<nil> timeout:0 collation:33 allowAllFiles:false allowOldPasswords:false clientFoundRows:false}", time.UTC},
-	{"@/", "&{user: passwd: net:tcp addr:127.0.0.1:3306 dbname: params:map[] loc:%p tls:<nil> timeout:0 collation:33 allowAllFiles:false allowOldPasswords:false clientFoundRows:false}", time.UTC},
-	{"/", "&{user: passwd: net:tcp addr:127.0.0.1:3306 dbname: params:map[] loc:%p tls:<nil> timeout:0 collation:33 allowAllFiles:false allowOldPasswords:false clientFoundRows:false}", time.UTC},
-	{"", "&{user: passwd: net:tcp addr:127.0.0.1:3306 dbname: params:map[] loc:%p tls:<nil> timeout:0 collation:33 allowAllFiles:false allowOldPasswords:false clientFoundRows:false}", time.UTC},
-	{"user:p@/ssword@/", "&{user:user passwd:p@/ssword net:tcp addr:127.0.0.1:3306 dbname: params:map[] loc:%p tls:<nil> timeout:0 collation:33 allowAllFiles:false allowOldPasswords:false clientFoundRows:false}", time.UTC},
-	{"unix/?arg=%2Fsome%2Fpath.ext", "&{user: passwd: net:unix addr:/tmp/mysql.sock dbname: params:map[arg:/some/path.ext] loc:%p tls:<nil> timeout:0 collation:33 allowAllFiles:false allowOldPasswords:false clientFoundRows:false}", time.UTC},
+	{"username:password@protocol(address)/dbname?param=value", "&{user:username passwd:password net:protocol addr:address dbname:dbname params:map[param:value] loc:%p tls:<nil> timeout:0 collation:33 allowAllFiles:false allowOldPasswords:false clientFoundRows:false columnsWithAlias:false}", time.UTC},
+	{"username:password@protocol(address)/dbname?param=value&columnsWithAlias=true", "&{user:username passwd:password net:protocol addr:address dbname:dbname params:map[param:value] loc:%p tls:<nil> timeout:0 collation:33 allowAllFiles:false allowOldPasswords:false clientFoundRows:false columnsWithAlias:true}", time.UTC},
+	{"user@unix(/path/to/socket)/dbname?charset=utf8", "&{user:user passwd: net:unix addr:/path/to/socket dbname:dbname params:map[charset:utf8] loc:%p tls:<nil> timeout:0 collation:33 allowAllFiles:false allowOldPasswords:false clientFoundRows:false columnsWithAlias:false}", time.UTC},
+	{"user:password@tcp(localhost:5555)/dbname?charset=utf8&tls=true", "&{user:user passwd:password net:tcp addr:localhost:5555 dbname:dbname params:map[charset:utf8] loc:%p tls:<nil> timeout:0 collation:33 allowAllFiles:false allowOldPasswords:false clientFoundRows:false columnsWithAlias:false}", time.UTC},
+	{"user:password@tcp(localhost:5555)/dbname?charset=utf8mb4,utf8&tls=skip-verify", "&{user:user passwd:password net:tcp addr:localhost:5555 dbname:dbname params:map[charset:utf8mb4,utf8] loc:%p tls:<nil> timeout:0 collation:33 allowAllFiles:false allowOldPasswords:false clientFoundRows:false columnsWithAlias:false}", time.UTC},
+	{"user:password@/dbname?loc=UTC&timeout=30s&allowAllFiles=1&clientFoundRows=true&allowOldPasswords=TRUE&collation=utf8mb4_unicode_ci", "&{user:user passwd:password net:tcp addr:127.0.0.1:3306 dbname:dbname params:map[] loc:%p tls:<nil> timeout:30000000000 collation:224 allowAllFiles:true allowOldPasswords:true clientFoundRows:true columnsWithAlias:false}", time.UTC},
+	{"user:p@ss(word)@tcp([de:ad:be:ef::ca:fe]:80)/dbname?loc=Local", "&{user:user passwd:p@ss(word) net:tcp addr:[de:ad:be:ef::ca:fe]:80 dbname:dbname params:map[] loc:%p tls:<nil> timeout:0 collation:33 allowAllFiles:false allowOldPasswords:false clientFoundRows:false columnsWithAlias:false}", time.Local},
+	{"/dbname", "&{user: passwd: net:tcp addr:127.0.0.1:3306 dbname:dbname params:map[] loc:%p tls:<nil> timeout:0 collation:33 allowAllFiles:false allowOldPasswords:false clientFoundRows:false columnsWithAlias:false}", time.UTC},
+	{"@/", "&{user: passwd: net:tcp addr:127.0.0.1:3306 dbname: params:map[] loc:%p tls:<nil> timeout:0 collation:33 allowAllFiles:false allowOldPasswords:false clientFoundRows:false columnsWithAlias:false}", time.UTC},
+	{"/", "&{user: passwd: net:tcp addr:127.0.0.1:3306 dbname: params:map[] loc:%p tls:<nil> timeout:0 collation:33 allowAllFiles:false allowOldPasswords:false clientFoundRows:false columnsWithAlias:false}", time.UTC},
+	{"", "&{user: passwd: net:tcp addr:127.0.0.1:3306 dbname: params:map[] loc:%p tls:<nil> timeout:0 collation:33 allowAllFiles:false allowOldPasswords:false clientFoundRows:false columnsWithAlias:false}", time.UTC},
+	{"user:p@/ssword@/", "&{user:user passwd:p@/ssword net:tcp addr:127.0.0.1:3306 dbname: params:map[] loc:%p tls:<nil> timeout:0 collation:33 allowAllFiles:false allowOldPasswords:false clientFoundRows:false columnsWithAlias:false}", time.UTC},
+	{"unix/?arg=%2Fsome%2Fpath.ext", "&{user: passwd: net:unix addr:/tmp/mysql.sock dbname: params:map[arg:/some/path.ext] loc:%p tls:<nil> timeout:0 collation:33 allowAllFiles:false allowOldPasswords:false clientFoundRows:false columnsWithAlias:false}", time.UTC},
 }
 
 func TestDSNParser(t *testing.T) {