allow var names to start with _ (#195)

Author: shueybubbles

pkg/sqlcmd/variables.go

@@ -285,7 +285,7 @@ func ValidIdentifier(name string) error {
 
 	first := true
 	for _, c := range name {
-		if !unicode.IsLetter(c) && (first || (!unicode.IsDigit(c) && !strings.ContainsRune(validVariableRunes, c))) {
+		if !unicode.IsLetter(c) && c != '_' && (first || (!unicode.IsDigit(c) && !strings.ContainsRune(validVariableRunes, c))) {
 			return fmt.Errorf("Invalid variable identifier %s", name)
 		}
 		first = false

pkg/sqlcmd/variables_test.go

@@ -104,6 +104,7 @@ func TestValidIdentifier(t *testing.T) {
 		{"A1", true},
 		{"A+", false},
 		{"A-_b", true},
+		{"__X", true},
 	}
 	for _, tst := range tests {
 		err := ValidIdentifier(tst.raw)